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\title{Kazlib---Reusable Components\\for C Programming}
\author{Kaz Kylheku}
\date{Release 1.20\\July 24, 2001}
\makeindex
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\begin{document}
\catcode`\_=11
\def\indextype#1{\index{#1@{\tt #1} type}}
\def\indexmacro#1{\index{#1@{\tt #1} macro}}
\def\indexobject#1{\index{#1@{\tt #1} object}}
\def\indexfunc#1{\index{#1@{\tt #1} function}}
\def\indexenum#1{\index{#1@{\tt #1} enum constant}}
\def\synopsis{\paragraph*{Synopsis}}
\def\constraints{\paragraph*{Constraints}}
\def\description{\paragraph*{Description}}
\def\example{\paragraph*{Example}}
\maketitle
\abstract{The aim of the Kazlib project is to provide a well-documented
programming interface featuring commonly needed programming abstractions,
accompanied by a high quality, portable reference implementation.
Kazlib consists of four independent components: a list module, a hash table
module, a dictionary module and an exception handling module. The reference
implementations of the first three of these are based on, respectively, the
following algorithms: doubly linked circular list with sentinel node,
extendible hashing, and red-black tree.}
\tableofcontents
\section{Introduction}
This document establishes the provisions required of an implementation of the
Kazlib library, and describes a reference implementation thereof.
This document specifies
\begin{itemize}
\item the names and types of identifiers and preprocessor symbols made
    available by each component;
\item identifier name spaces reserved for future use by each component;
\item the interface syntax and semantics of each component operation;
\item the conditions required for the well-defined execution of each operation;
\item the externally visible behavior of each component, including global
    side effects and the effects on the subject data structures;

\item and the implementation language of Kazlib.
\end{itemize}
Furthermore, this document describes, but does not specify
\begin{itemize}
\item the implementation details of structure objects manipulated by the
    operations of each component;
\item objects and functions that are defined by the implementation of
    each component but are not externally visible;
\item the algorithms and implementation details of the operations.
\end{itemize}
Finally, this document does {\em not\/} specify or describe
\begin{itemize}
\item the specific choices for parameters which may be adjusted by an
    installation or implementation of Kazlib.
\item the size of any data structure which will exceed the capacity of
    a particular installation.
\item the mechanisms or procedures for the translation of Kazlib and
    their integration with other translation units.
\end{itemize}

\section{References}
\label{sec:references}

\begin{trivlist}
\item ISO 9899:1990, {\it Programming Languages---C.}
\item {\it Introduction to Algorithms}, Thomas H. Cormen, Charles E.
Leiserson, Ronald L. Rivest, eighth printing, 1992.
\end{trivlist}

\section{Definitions and conventions}
The following terms shall be interpreted in accordance with the definitions
below. Other terms appearing in this document shall be defined upon their
first mention, indicated by {\it italic\/} type. Any terms not explicitly
defined in this document should be interpreted according to ISO 9899-1990,
clause 3. Failing that, they should be interpreted according to other works
listed in section \ref{sec:references}.
\nobreak
\defsubsection{implementation}: A library and set of C language headers
which conforms to the specifications of this Document.
\index{production mode}
\indexmacro{NDEBUG}
\defsubsection{production mode}: A mode of operating the implementation
in such a way that maximum efficiency of execution is achieved at the expense
of the verification of constraints. An implementation shall provide
a production mode, which is enabled in an implementation-defined
manner.\footnote{An implementation may have to supply a separate set of
libraries for production and for verification use, for instance. The
manner of selecting libraries varies with each programming environment.}  Each
translation unit of the program which includes a Kazlib header shall ensure that the macro {\tt
NDEBUG} is defined prior to the inclusion of that header, otherwise the
implementation is not said to be operated in production mode.
\index{verification mode}
\defsubsection{verification mode}: A mode of operating the implementation in
such a way that maximum error checking is obtained at the cost of
execution efficiency. An implementation shall provide a verification mode, which
is enabled in an implementation-defined manner. If any translation unit which
includes a Kazlib header defines the macro name {\tt NDEBUG}\footnote{The
intent is that the standard {\tt assert} macro may be exploited
by the implementation's headers for the purpose of provisioning verification
mode.} prior to including that header, the implementation is not said to be in
verification mode. The least requirements of a Kazlib implementation operated
in verification mode, is that it shall stop translation or execution of any
program which violates a constraint. 
\index{undefined behavior}
\defsubsection{undefined behavior}: Behavior of a program, upon violation of a
requirement with respect to the use of Kazlib, or upon use of corrupt or
incorrect data, for which this document does not impose any requirements.
Additional undefined behaviors are:
\begin{itemize}
\item any behavior that is undefined by the C language standard;
\item evaluation of an object whose contents are indeterminate;
\item a violation of any explicit constraint stated in
this document, if that program was built using Kazlib in production
mode;\footnote{The intent is that violations of constraints are diagnosed by
the implementation in verification mode, and hence do not lead to undefined
behavior.}
\item a violation of any requirement stated in this document that
is not designated as a constraint, and is introduced using the word
{\it shall}; and
\item any other construct for which no definition of behavior can be deduced
from this document.
\end{itemize}
If a program invokes undefined behavior of any kind, the Kazlib implementation
is absolved from any requirements as to what events should ensue.  The
implementation may respond by invoking undefined behavior in the C language
sense, or it may detect the behavior and terminate with a diagnostic message.
\defsubsection{implementation-defined}: An adjective which, when appearing
in the description of a feature, represents a requirement that the
implementor must supply a definition, and document that
definition. This adjective is applied to both behavior and to results.
Implementation-defined behavior is behavior which depends on the
characteristics of an implementation.\footnote{It is not considered adequate
for the implementor to allow implementation-defined behavior to produce
unpredictable effects or to terminate the program when such behavior is
invoked.}  When said of a result,
implementation-defined means that a value is successfully computed, but depends
on the characteristics of the implementation. It is possible for the presence of a
requirement on a program to be described as implementation-defined, giving the
implementor a choice whether to make that requirement or not. If a program
violates a requirement whose presence is implementation-defined, that program's
behavior is undefined in any implementation which elects to in fact impose that
requirement.
\index{implementation-defined}
\defsubsection{unpredictable result}: A successfully computed value which is
unreliable because some procedure or data failed to satisfy a property required
by the computation.
\defsubsection{constraint}: A semantic restriction with which a program must
comply. Some sections of this Document contain paragraphs under the heading
{\it Constraints\/} which list all constraints pertaining to the described
feature. When operated in production mode, the Kazlib implementation
is not required to diagnose constraint violations. When operated in
verification mode, the Kazlib implementation must halt translation or
execution of a program which violates a constraint.
\index{constraint}
\defsubsection{comparison function}: A function which accepts two arguments
\index{comparison function}
of type \verb|const void *| and returns a value of type int based on
a ranking comparison of these arguments, and which satisfies the following
additional semantic properties. If the two arguments are deemed to be equal, the
function must return zero. If the first argument is determined to have a
greater rank than the second, a positive value is returned. Otherwise if the
first argument is determined to have a lesser rank than the second, a negative
value is returned. The rank is computed as if each value has associated with it
an integer, not necessarily unique, and as if these integers are compared for ordinary equality or
inequality when values are said to be compared.  The assignment of integers is
up to the designer of the comparison function, and does not change between
successive invocations of the function.\footnote{Of course, an actual
comparison function need not assign actual integer ranks to data items, but it
must behave as if such ranks were assigned.}
If a comparison function is invoked in the context of an operation on some data
structure, it shall not invoke any operation on any component of that same
structure.\footnote{Thus, if a comparison function is invoked from, for
instance, {\tt list_sort}, it must not call any list operations that 
inspect or modify the list being sorted, or any of its constituent nodes.}
\defsubsection{opaque data type}: A data type whose precise definition is
not documented, and which is intended to be manipulated only using the
documented interface, which consists of a set of functions.  Many data types in
Kazlib are described as opaque. A program which bypasses the documented
interfaces in inspecting or manipulating these data types invokes undefined
behavior, and is not portable among Kazlib implementations.
\defsubsection{user}: \index{user} The program which uses Kazlib.
\defsubsection{user data}: \index{user data} Data provided by the program
to which Kazlib stores a pointer, but otherwise does not inspect or modify.

\section{Environment}
\label{sec:environment}

The translation and use of Kazlib requires a conforming, hosted implementation
of the C language which meets the following additional minimal requirements:
\begin{enumerate}
\item The C implementation distinguishes external names by at least their
initial 15 characters\footnote{The ISO 9899:1990 standard demands only that
external names be distinguished by their initial six characters.}. External
names that are distinct in their first 15 characters are treated by the
implementation as distinct names.  Upper and lower case letters in external
identifiers need not be treated as distinct.
\item The C implementation does not claim the identifier \verb|__cplusplus|
for its internal use as a preprocessor symbol or keyword.
\end{enumerate}
If Kazlib headers are used by a C++ program, the C++ implementation
meets these additional requirements:
\begin{enumerate}
\item the C++ implementation identifies itself by predefining the preprocessor
symbol \verb|__cplusplus|;
\item the C++ implementation is be capable of linkage against
the C implementation with which the Kazlib source files units were translated.
\end{enumerate}
The Kazlib headers shall not make use of any names that are claimed
by the C++ programming language, and shall ensure that the \verb|extern "C"|
mechanism is used for all declarations when they are included into a C++
translation unit, or otherwise provide compatibility with C++.\footnote{The
intent is that the Kazlib implementation could, in principle, provide 
a separate set of headers for use with each language.}

In programming environments that support the programming mechanism of multiple
threads of execution an implementation of Kazlib may be designated as {\it
thread safe}.  To be called thread safe, it must guarantee that the use of an
object by one thread cannot visibly interact or interfere with the concurrent
or interleaved use of another object by another thread. If a Kazlib
implementation that is not thread safe is provided for an environment which
supports threads, it shall be accompanied by documentation which describes
the extent of this limitation.

A Kazlib implementation can also be designated as being {\it async safe}.
The minimum requirement for this designation is that an operation on an object
can be interrupted by delivery of an asynchronous signal and from within the
catching function for that signal, it is safe to perform an operation on
another object.  An implementation shall document that it is async safe,
or the extent to which it fails to be async safe.

\section{General restrictions}

\subsection{Headers}

The Kazlib headers may be included in any order, and may be included more than
once. Prior to the inclusion of a Kazlib header, the translation unit shall not
define any macro name that has the same spelling as a C language keyword. The
Kazlib headers may behave as though they include arbitrary standard C headers,
so any requirements related to the inclusion of standard headers apply to
Kazlib headers.  A header shall be included before the first reference to any
of the functions, types or macros that it defines.

If one or more preprocessor symbols whose names begin with the sequence
\verb|KAZLIB_| are defined prior to the inclusion of a Kazlib header,
the behavior is implementation-defined.

\subsection{Reserved macros}

A Kazlib header defines all of the macros explicitly listed in the section of
this document that defines the contents of that header. It may also define
additional macros that belong to the macro namespace reserved by that header.
The translation unit that includes the header shall not \verb|#define| or
\verb|#undef| any of these macros.

A header may define function-like macros that supplement existing functions,
provided that such macros do not cause multiple evaluation of arguments except
as explicitly permitted, and are safe to use wherever the corresponding
function call would be. These function-like macros may be subject to
\verb|#undef|.\footnote{In principle, an implementation may provide, within the
reserved namespaces, additional functions not specified in this document, and
function-like macro equivalents of these functions. A program that uses such
identifiers in a block or function scope should use {\tt \#undef} on these
identifiers prior to their use.}

\subsection{Reserved symbols}

Each Kazlib header provides file scope declarations for the typedef names,
struct tags, enum constants and function names listed in its corresponding
section in this document. Moreover, each header may define additional such
names that fall into the documented reserved namespaces.

The behavior is undefined if a translation unit that includes a Kazlib header
defines any identifier that is the same as an identifier reserved by the header
in the same scope and namespace.\footnote{Therefore, it is permitted to redeclare
or redefine the identifiers reserved by a previously included Kazlib header,
provided that the declarations or definitions are in a different namespace or
scope. Reserved names may be redeclared in a block scope, or used as
statement labels which have function scope and are in their own namespace.}

The behavior is also undefined if the program contains a definition of an
object or function with external linkage whose name matches an external object
of unction defined  by Kazlib component that is used as part of the
program, or whose name is in a namespace reserved by that
component.\footnote{This restriction exists whether or not the corresponding Kazlib
header is included.} 

Lastly, the behavior is undefined if a translation unit defines a macro whose
name is in the space of reserved symbols of a Kazlib header that is included in
that translation unit.

\subsection{Argument aliasing}

Kazlib provides functions that operate on objects of various types.  Pointers
to objects are passed to these functions, thereby giving rise to the
possibility of {\it aliasing}---passing of objects that wholly or partially
overlap.  The program shall not present aliased objects to any Kazlib function.
Objects of distinct types shall not be aliased in a function call under any
circumstances.
The aliasing of two or more objects of compatible type is permitted only as
explicitly documented in the description of a function; in all such
circumstances, only exact overlapping is permitted.\footnote{That is to say,
where explicitly allowed, a pointer to the same object may be specified for two
(or more) parameters of like type.}

\subsection{Object initialization}

The Kazlib opaque data types can only be initialized with the initialization
functions provided by the Kazlib library, or by implementation-defined
initialization functions.\footnote{Of course, the use of implementation-defined
functions results in programs that are not portable among library
implementations.} An opaque object that is initialized by a method other than
by being passed to an appropriate initialization function, or that is not
initialized at all, has indeterminate contents.  A pointer to an object having
indeterminate contents may be passed to an initialization function; the object
then has well-determined contents.

An object whose initialization function is capable of indicating failure is
considered indeterminate if the attempt to initialize that object using that
function does in fact fail. The program shall not attempt to deinitialize such
an object. The implementation shall reclaim any resources that were allocated
for an object whose initialization failed. This reclamation need
not be immediate, but may be delayed; however, the delay shall not
give rise to the possibility of resource leaks in any correct program.

Those objects for which deinitialization operations are defined should be
subject to these operations when these objects are no longer needed.  Failure
to apply the deinitialization functions may result in the leakage of resources.

\subsection{Object copying}

Certain data types may be sensitive to their own location in memory.  This
means that copying their values by assignment or \verb|memcpy| results in the
copy having an indeterminate value which cannot be used.  All opaque types in
Kazlib are assumed to have this property; copying the value of an opaquely
typed object to another suitably typed object causes the destination
object to have indeterminate contents. 

\section{List component}

The List component provides a set of functions, macros and type declarations
which together provide a library for maintaining a possibly empty ordered set
of elements, called a {\it list}. This list has the following properties:
\index{List}\begin{enumerate}
\item If the list is not empty, a first and last element can be identified.
    In a list having only one element, that one element is both the first and
    last element.
\item Each element that is not the last element has another element as its
    {\it successor}.
    \index{successor!of a list element}
    \index{List!successor of an element}
\item Each element that is not the first element has a {\it
    predecessor}.
    \index{predecessor!of a list element}
    \index{List!predecessor of an element}
\item No element is the predecessor or successor of more than one element.
\item If one element is the successor of another, the other is necessarily the
    predecessor of the first.
\item Each element is associated with arbitrary {\it satellite\/} data.
\end{enumerate}
The {\it size} of a list, also known as the {\it list count}, is simply the
number of elements contained in it.\index{size!of a list}\index{List!count}

A list imposes a maximum value on the number of nodes that may be in it
simultaneously. This is known as the list's {\it capacity}. A list that
has the maximum number of nodes is said to be full.

\subsection{Interface}

\subsubsection{The {\tt list.h} header}

Each C or C++ translation unit that is to use the functionality of
the List component shall include the header \verb|list.h|. This header
shall contain declarations of types and external functions, and definitions of
macros.
The following typedef names shall be defined:\index{List!typedef names}
\index{typedefs!defined by List}
\begin{verbatim}
    list_t                      listcount_t
    lnode_t                     lnodepool_t
\end{verbatim}
In addition, the following structure tags may be defined:\index{List!tag names}
\index{tags!defined by List}
\begin{verbatim}
    struct list_t
    struct lnode_t
    struct lnodepool_t
\end{verbatim}
The following external function names shall be declared:
\index{List!function names}\index{functions!defined by List}
\begin{verbatim}
    list_append                 list_prev                          
    list_contains               list_process                       
    list_count                  list_return_nodes                  
    list_create                 list_sort                          
    list_del_first              list_find
    list_del_last               list_transfer                      
    list_delete                 list_verify                        
    list_destroy                lnode_borrow                       
    list_destroy_nodes          lnode_create                       
    list_extract                lnode_destroy                      
    list_first                  lnode_get                          
    list_init                   lnode_init                         
    list_ins_after              lnode_is_in_a_list                 
    list_ins_before             lnode_pool_create                  
    list_is_sorted              lnode_pool_destroy                 
    list_isempty                lnode_pool_init                    
    list_isfull                 lnode_pool_isempty                 
    list_last                   lnode_pool_isfrom                  
    list_merge                  lnode_put                          
    list_next                   lnode_return                       
    list_prepend                
\end{verbatim}
The following preprocessor symbols (macros) shall be defined:
\index{List!macro names}\index{macros!defined by List}
\indexmacro{LISTCOUNT_T_MAX}
\indexmacro{LIST_H}
\begin{verbatim}
    LISTCOUNT_T_MAX
    LIST_H\end{verbatim}
\index{symbols!reserved by List}\index{List!reserved symbols}
Macro identifiers which begin with the upper-case prefix \verb|LIST| are
reserved for future extensions to the \verb|list.h| header, as are
names in the ordinary and tag namespaces which begin with
\verb|list_| or \verb|lnode_|. External names which begin with \verb|list_| or
\verb|lnode_| are reserved by the Kazlib library regardless of what header
files are included.

\subsubsection{The {\tt list_t} type}

\indextype{list_t}
The type \verb|list_t| is an opaque data type which maintains information about the
current state of a single list.  A list consists of an instance of the
\verb|list_t| type, plus zero or more instances of the type \verb|lnode_t|. An
instance of the \verb|list_t| type can be dynamically created using the
\verb|list_create| function, and destroyed by the \verb|list_destroy| function.
Alternately, the program can declare an object of type \verb|list_t| and have
it initialized via the \verb|list_init| function. 

\subsubsection{The {\tt listcount_t} type}

\indextype{listcount_t}
\indexmacro{LISTCOUNT_T_MAX}
The type \verb|listcount_t| is an unsigned integral type which represents
the number of nodes in a list. The specific choice of unsigned integral type
is implementation defined. The \verb|LISTCOUNT_T_MAX| macro expands to a
constant expression of type \verb|listcount_t| which specifies the maximum
value of that type.\footnote{For example, if the implementation defines
{\tt listcount_t} as an alias for the type unsigned long, then 
{\tt LISTCOUNT_T_MAX} must have the same value as {\tt ULONG_MAX}.}

\subsubsection{The {\tt lnode_t} type}

\indextype{lnode_t}
The type \verb|lnode_t| is an opaque type that represents a single node of a
list. A node contains a a reference to satellite data provided by the user,
and also stores the key that is associated with the node when it is inserted.
Nodes may be dynamically created by the \verb|lnode_create| function.
Alternately, the program may supply an \verb|lnode_t| object that can be
initialized by the \verb|lnode_init| function. 

\subsubsection{The {\tt lnodepool_t} type}

\indextype{lnodepool_t}
The \verb|lnodepool_t| type provides an alternate method for supplying list
nodes to the application. A user-supplied or dynamically allocated fixed size
array of nodes is converted into a a {\it pool\/} of nodes from which free
nodes may be obtained and to which they may be returned. A user-supplied node
pool is created by the function \verb|lnode_pool_init| which requires a pointer
to an object of type \verb|lnode_pool_t|, a pointer to the first element of an
array of \verb|lnode_t| objects, as well as an integer representing the size of
the array. Alternately, the function \verb|lnode_pool_create| will dynamically
allocate an object of type \verb|lnode_pool_t| containing the specified number
of list nodes. 

\subsubsection{The {\tt list_append} function}

    \indexfunc{list_append}
    \index{List!appending a node}
    \index{append node to list}
    \synopsis
    \begin{verbatim}
    void list_append(list_t *, lnode_t *);\end{verbatim}

    \constraints
    The second argument shall not refer to a node that is already in a list
    or in a list node pool. The first argument shall not refer to a list
    that is full.

    \description
    The append operation causes the node pointed at by the second
    argument to become the last node in the list pointed at by the first
    argument.\footnote{That is to say, after the operation, the
    {\tt list_last} function, when applied to the list, shall return a pointer
    to that node.}

    If the first argument is an expression with side effects, the behavior
    is undefined.\footnote{Thus, the implementation may provide a macro
    version of {\tt list_append} which evaluates the first argument
    more than once.}
    \index{macros!and side effects}

\subsubsection{The {\tt list_contains} function}

    \indexfunc{list_contains}
    \index{List!testing for presence of node}
    \nobreak
    \synopsis
    \begin{verbatim}
    int list_contains(list_t *, lnode_t *node);\end{verbatim}
    \nobreak
    \description
    \nobreak
    The \verb|list_contains| function shall return 1 if the node
    pointed at by the second argument is in the list pointed at by the first
    argument.  Otherwise, it shall return 0.

\subsubsection{The {\tt list_count} function}

    \indexfunc{list_count}
    \index{List!count}
    \index{List!size}
    \synopsis
    \begin{verbatim}
    listcount_t list_count(list_t *);\end{verbatim}

    \description

    The \verb|list_count| function returns a value which represents the number
    of nodes currently stored in the list pointed at by the argument.

\subsubsection{The {\tt list_create} function}

    \indexfunc{list_create}
    \index{List!creation of}
    \index{create!list object}
    \synopsis
    \begin{verbatim}
    list_t *list_create(listcount_t);\end{verbatim}

    \description
    The \verb|list_create| function instantiates and initializes an object of
    type \verb|list_t|, and returns a pointer to it unless insufficient
    resources exist for the creation of the object, in which case a null
    pointer is returned.

    The value of the function's argument establishes, for the entire duration
    of the list object, its capacity.

    The newly created list object is empty.

\subsubsection{The {\tt list_del_first} function}

    \index{List!first node}
    \indexfunc{list_del_first}
    \index{List!deletion}
    \index{delete!first node of a list}
    \synopsis
    \begin{verbatim}
    lnode_t *list_del_first(list_t *);\end{verbatim}

    \constraints
    The argument shall not point to an empty list.

    \description
    The \verb|list_del_first| function removes the first node from the
    list pointed at by the argument and returns a pointer to that
    node. 

    If the argument is an expression with side effects, the behavior is
    undefined.\index{macros!and side effects}

\subsubsection{The {\tt list_del_last} function}

    \index{List!last node}
    \indexfunc{list_del_last}
    \index{List!deletion}
    \index{delete!last node of a list}
    \synopsis
    \begin{verbatim}
    lnode_t *list_del_last(list_t *);\end{verbatim}

    \constraints
    The argument shall not point to an empty list.

    \description
    The \verb|list_del_last| function removes the last node from the list
    specified by the argument, and returns a pointer to that node. If,
    prior to the operation, that node had a predecessor, that predecessor
    shall become the new last node of the list. Otherwise, the list
    shall become empty.

    The new value of the list count shall be one less than its value
    prior to the call to this function.

    If the argument is an expression with side effects, the behavior is
    undefined.\index{macros!and side effects}

\subsubsection{The {\tt list_delete} function}

    \indexfunc{list_delete}
    \index{List!deletion}
    \index{delete!arbitrary node of a list}
    \synopsis
    \begin{verbatim}
    lnode_t *list_delete(list_t *, lnode_t *);\end{verbatim}

    \constraints
    The second argument shall point to a node that is inside the list
    pointed at by the first argument.

    \description
    The \verb|list_delete| function removes the node pointed at by its
    second argument from the list pointed at by its first argument.
    A pointer to the deleted node is returned.

\subsubsection{The {\tt list_destroy} function}

    \indexfunc{list_destroy}
    \index{List!destruction of}
    \synopsis
    \begin{verbatim}
    void list_destroy(list_t *);\end{verbatim}

    \constraints
    The argument shall point to an empty list.

    \description
    The empty list pointed at by the argument is destroyed. If the list has
    not been created by a call to the \verb|list_create| function, the
    behavior is undefined.

    A pointer that previously referred to a list that has been disposed by
    \verb|list_destroy| has an indeterminate value.

\subsubsection{The {\tt list_destroy_nodes} function}

    \indexfunc{list_destroy_nodes}
    \synopsis
    \begin{verbatim}
    void list_destroy_nodes(list_t *);\end{verbatim}

    \description
    The nodes, if any, contained in the list pointed at by the argument are
    disposed of as if by a call to the \verb|lnode_destroy| function. If any
    node contained in the list was created by means other than the
    \verb|lnode_create| function, the behavior is undefined.

    After the operation, the list is empty.

    Any pointer that referred to any of the destroyed nodes takes on an
    indeterminate value.

\subsubsection{The {\tt list_extract} function}

    \index{List!node range extraction}
    \indexfunc{list_extract}
    \synopsis
    \begin{verbatim}
    void list_extract(list_t *, list_t *, lnode_t *, lnode_t *);\end{verbatim}

    \constraints
    The second argument points to the {\it source list}. The third
    argument is either null, or points to a node that is an occupant
    of the source list. This node is called the {\it starting node}.
    The fourth argument is either null, or points to a node that is
    an occupant of the source list. This node is called the {\it ending
    node}. If the starting node and ending node are both specified, and are
    distinct nodes, then the starting node shall appear earlier in the source
    list than the ending node.

    The transfer request shall not call for the capacity of the  destination
    list to be exceeded.

    \description
    The \verb|list_extract| function moves nodes from the source
    list to the {\it destination list\/} pointed at by the first
    argument.\footnote{This right-to-left direction of transfer is consistent
    with the semantics of standard C library functions such as {\tt memmove} or
    {\tt strcpy}.}

    If the third and fourth arguments are not null, the entire range of nodes
    from the starting node and to the ending node, inclusive, is transferred
    from the source list to the end of the destination list, where they appear
    in their original order. Other nodes in the source list, if any, are
    unaffected.

    If the third and fourth arguments both point to the same node, that
    node alone is transferred to the end of the destination list.

    If either the third argument or the fourth argument is null, or both are null,
    no transfer of nodes takes place.

    The source and destination list may be the same object.

\subsubsection{The {\tt list_first} function}

    \index{List!first node}
    \indexfunc{list_first}
    \synopsis
    \begin{verbatim}
    lnode_t *list_first(list_t *);\end{verbatim}

    \description
    If the list pointed at by the argument is an empty list, a null pointer
    is returned. Otherwise, a pointer to the first node in that list is
    returned.

    If the argument is an expression with side effects, the behavior is
    undefined.\index{macros!and side effects}

\subsubsection{The {\tt list_init} function}

    \indexfunc{list_init}
    \synopsis
    \begin{verbatim}
    list_t *list_init(list_t *, listcount_t);\end{verbatim}

    \constraints
    The second argument shall not have a zero value.

    \description
    The \verb|list_init| function initializes the list object pointed at by the
    first argument, turning it into a valid, empty list. If the object is an
    already initialized list, the behavior is undefined. A list returned by
    \verb|list_create| is considered initialized. The second argument 
    specifies the maximum number of nodes that may simultaneously occupy the
    list.

    The value returned is that of the first argument.

\subsubsection{The {\tt list_ins_after} function}

    \indexfunc{list_ins_after}
    \index{insert!node into list}
    \index{List!insertion}
    \synopsis
    \begin{verbatim}
    void list_ins_after(list_t *, lnode_t *, lnode_t *);\end{verbatim}

    \constraints
    The first argument shall point to a list that is not already full.  The
    second argument shall point to a node, called the {\it new node}, that is not
    already an occupant of the list pointed at by the first argument, nor
    of any other list or node pool object. The third
    argument shall point to a node, called the {\it reference node}, that is an
    occupant of the list.

    \description
    The new node becomes an occupant of the list, such that its predecessor
    is the reference node. If the reference node has a successor, the
    new node is inserted between the reference node and that successor.
    Otherwise, the new node becomes the last node of the list.

\subsubsection{The {\tt list_ins_before} function}

    \indexfunc{list_ins_before}
    \index{insert!node into list}
    \index{List!insertion}
    \synopsis
    \begin{verbatim}
    void list_ins_before(list_t *, lnode_t *, lnode_t *);\end{verbatim}

    \constraints
    The first argument shall point to a list that is not already full.  The
    second argument shall point to a node, called the {\it new node}, that is not
    already an occupant of the list pointed at by the first argument, nor
    of any other list or node pool object. The third
    argument shall point to a node, called the {\it reference node}, that is an
    occupant of the list.

    \description
    The new node becomes an occupant of the list, such that its successor
    is the reference node. If the reference node has a predecessor, the
    new node is inserted between the reference node and that predecessor.
    Otherwise, the new node becomes the first node of the list.
    
\subsubsection{The {\tt list_is_sorted} function}
\label{list:is:sorted}
    \indexfunc{list_is_sorted}

    \synopsis
    \begin{verbatim}
    int list_is_sorted(list_t *,
            int (const void *, const void *));\end{verbatim}

    \description
    The first argument points to a list object. The second is assumed to
    point to a comparison function.
    
    If the list has exactly one node or is empty, $1$ is returned
    unconditionally.  Otherwise, nodes of the list are examined to
    determine whether they are in a sorted order according to the comparison
    function. This is true if the integer ranks of their data items,
    examined from the first node of the list through to the last node, form a
    monotonically increasing sequence. If the nodes are in order, the value $1$
    is returned. Otherwise $0$ is returned.
    
    If the list has two or more nodes, and the second argument is a pointer to
    a function that has the correct type, but does not satisfy the semantic
    properties of a comparison function, the result is unpredictable, but is
    guaranteed to be one of the values~$0$~or~$1$. 

\subsubsection{The {\tt list_isempty} function}

    \indexfunc{list_isempty}
    \synopsis
    \begin{verbatim}
    int list_isempty(list_t *);\end{verbatim}

    \description
    The \verb|list_isempty| function returns $1$ if the list pointed at by
    the first argument is empty. Otherwise it returns $0$.

\subsubsection{The {\tt list_isfull} function}

    \indexfunc{list_isfull}
    \synopsis
    \begin{verbatim}
    int list_isfull(list_t *);\end{verbatim}

    \description
    The \verb|list_isfull| function returns $1$ if the list pointed at by
    the first argument is full. Otherwise it returns $0$.
    A list is considered full when it contains the maximum number of nodes
    that was specified upon its initialization.

    If the argument is an expression with side effects, the behavior is
    undefined.\index{macros!and side effects}

\subsubsection{The {\tt list_last} function}

    \index{List!last node}
    \indexfunc{list_last}
    \synopsis
    \begin{verbatim}
    lnode_t *list_last(list_t *);\end{verbatim}

    \description
    If the list pointed at by its first argument is empty, the \verb|list_last|
    function returns a null pointer. Otherwise it returns a pointer to the
    last node.

    If the argument is an expression with side effects, the behavior is
    undefined.\index{macros!and side effects}

\subsubsection{The {\tt list_merge} function}

    \index{List!merge operation}
    \indexfunc{list_merge}
    \synopsis
    \begin{verbatim}
    void list_merge(list_t *, list_t *,
            int (const void *, const void *));\end{verbatim}

    \constraints
    The list pointed at by the first argument is called the {\it destination
    list}. The second argument points to the {\it source list}. The third
    argument points to a comparison function.  The sum of the number of nodes
    occupying the source list and the destination list shall not exceed the
    maximum number of nodes that are permitted to occupy the destination list.
    Furthermore, both the source and destination list shall be sorted such that
    a call to \verb|list_is_sorted| given a pointer to either list as a first
    argument, and the pointer to the comparison function as its second
    argument, shall yield the value $1$.

    \description
    Nodes from the sorted source list are merged into the sorted destination
    list. After the operation, the source list is empty and the destination
    list contains all of the nodes it contained prior to the operation, as well
    as all of the nodes that the source list contained. The nodes are in sorted
    order according to the comparison function.

    If the third argument is a pointer to a function that has the correct type,
    but does not fulfill the semantic properties of a comparison function, the
    order of the nodes in the destination list is unpredictable.

    If the source and destination list are the same object, the
    \verb|list_merge| operation has no effect.

\subsubsection{The {\tt list_next} function}

    \indexfunc{list_next}
    \synopsis
    \begin{verbatim}
    lnode_t *list_next(list_t *, lnode_t *);\end{verbatim}

    \constraints
    The node pointed at by the second argument is an occupant of the list pointed
    at by the first argument.

    \description
    If the node pointed at by the second argument has a successor, a pointer to
    that successor is returned. Otherwise, a null pointer is returned.

    If the second argument is an expression which has side effects, the behavior
    is undefined.\index{macros!and side effects}

\subsubsection{The {\tt list_prepend} function}

    \indexfunc{list_prepend}
    \index{List!prepending a node}
    \index{prepend node to list}
    \synopsis
    \begin{verbatim}
    void list_prepend(list_t *, lnode_t *);\end{verbatim}

    \constraints
    The second argument shall not refer to a node that is already in a list
    or in a list node pool. The first argument shall not refer to a list
    that is full.

    \description
    The prepend operation causes the node pointed at by the second
    argument to become the first node in the list pointed at by the first
    argument. After the operation, the \verb|list_first| function, when
    applied to the list, shall return a pointer to that node.
    If, prior to to the operation, the list is empty, then the prepended node
    shall become the first node in that list, otherwise, the prepended node
    becomes the predecessor of what was previously the first node.

    If the first argument is an expression with side effects, the behavior
    is undefined.\index{macros!and side effects}

\subsubsection{The {\tt list_prev} function}

    \indexfunc{list_prev}
    \synopsis
    \begin{verbatim}
    lnode_t *list_prev(list_t *, lnode_t *);\end{verbatim}

    \constraints
    The node pointed at by the second argument is an occupant of the list pointed
    at by the first argument.

    \description
    If the node pointed at by the second argument has a predecessor, a pointer to
    that predecessor is returned. Otherwise, a null pointer is returned.

    If the second argument is an expression which has side effects, the behavior
    \index{macros!and side effects}
    is undefined.

\subsubsection{The {\tt list_process} function}

    \indexfunc{list_process}
    \synopsis
    \begin{verbatim}
    void list_process(list_t *, void *,
            void (*)(list_t *, lnode_t *, void *));\end{verbatim}
    \nobreak
    \description
    The \verb|list_process| function iterates over the nodes of a list,
    and for each node invokes a callback function.\footnote{In most cases,
    it is more convenient and preferable to 
    iterate over the list using explicit calls to {\tt list_first}
    and {\tt list_next}.}
    The second argument is a {\it context pointer\/} which can have any value.
    The third argument of
    \verb|list_process| shall be a pointer to a function which is compatible
    with the specified type. If the list contains one or more nodes,
    then the function is invoked once for each node, in order from first
    to last. On each invocation, the first argument of the callback is a
    pointer to the list; the second argument is a pointer to a node, called
    the {\it subject node}; and the third argument repeats the context pointer
    value that was originally passed to \verb|list_process|.

    The callback function may delete the subject node by, for instance, calling
    \verb|list_delete|. It may insert new nodes to any place in the list;
    however, if such an insertion causes the subject node to acquire
    a new successor, it is implementation-defined whether upon returning
    from the callback function, the traversal shall continue with the
    new successor, or with the original successor.
    
    The callback function, and any function invoked from the callback
    function, shall not destroy the list or make any modifications
    other than the insertion of new nodes, or the deletion of the 
    subject node.

    The callback function may recursively invoke \verb|list_process| for the
    same list or for a different list; the callback invocations arising out of
    the nested call inherit all of the restrictions of the outer callback in
    addition to being subject to the usual restrictions.\footnote{This means,
    for instance, that if two callbacks are in progress for different
    subject nodes from the same list, the inner callback may not delete
    its subject node, because it inherits the restriction that the only
    permitted deletion is the outer callback's subject node.}

    The callback function may freely operate on a different list,
    subject to any inherited restrictions.

\subsubsection{The {\tt list_return_nodes} function}

    \indexfunc{list_return_nodes}
    \synopsis
    \begin{verbatim}
    void list_return_nodes(list_t *, lnodepool_t *);\end{verbatim}

    \description

    Every node in the list specified by the first argument
    is returned to the node pool specified by the second argument
    If the list contains a node that has not been allocated
    from that node pool, the behavior is undefined.

\subsubsection{The {\tt list_sort} function}

    \index{List!sort operation}
    \indexfunc{list_sort}
    \synopsis
    \begin{verbatim}
    void list_sort(list_t *, int (const void *, const void *));\end{verbatim}

    \description

    The \verb|list_sort| function changes the order of the nodes of the list
    specified by the first argument according to the comparison function
    pointed at by the second argument. 

    If the list is empty, or contains only one node, the comparison function is
    not called.

    Whenever the comparison function is invoked, its arguments are are the data
    pointers stored in two distinct nodes of the list.

\subsubsection{The {\tt list_find} function}

    \index{List!find operation}
    \indexfunc{list_find}
    \synopsis
    \begin{verbatim}
    lnode_t *list_find(list_t *,
           const void *, int (const void *, const void *));\end{verbatim}

    \description

    The \verb|list_find| function exhaustively searches the key for a node
    whose satellite data matches a search key according to the comparison
    function. The first argument is the list to be searched, the second
    argument specifies the search key and the third argument is a pointer
    to the comparison function.

    The comparison function is invoked to compare the key against the
    satellite data of successive nodes of the list, starting with the first
    node. A pointer to the first node for which the comparison function returns
    zero is returned.

    If the list is empty, or the comparison function returns non-zero for
    each item, a null pointer is returned.

\subsubsection{The {\tt list_transfer} function}

    \index{List!node transfer}
    \indexfunc{list_transfer}
    \synopsis
    \begin{verbatim}
    void list_transfer(list_t *, list_t *, lnode_t *);\end{verbatim}

    \constraints
    The third argument is either null, or it points at a node which is an
    occupant of the list pointed at by the second argument.

    The transfer request shall not call for the capacity of the  destination
    list to be exceeded.

    \description
    The \verb|list_transfer| function moves nodes from the list
    pointed at by the second argument to the list pointed at by
    the first argument.

    If the third argument is not null, it specifies the node in the source list
    at which the transfer begins. That node, its successor, and all 
    subsequent nodes, are transferred to the end of the destination list where
    they appear in their original order. Other nodes in the source list are
    unaffected.

    If the third argument is null, no transfer of nodes takes place.

    The source and destination list may be the same object.

    If \verb|DL|, \verb|SL| and \verb|SN| are appropriately typed expressions,
    the function call

\begin{verbatim}
    void list_transfer(DL, SL, SN);
\end{verbatim}
    is equivalent to 
\begin{verbatim}
    list_extract(DL, SL, SN, list_last(SL));
\end{verbatim}
    except that \verb|SL| is evaluated only once.

\subsubsection{The {\tt list_verify} function}

    \indexfunc{list_verify}
    \synopsis
    \begin{verbatim}
    int list_verify(list_t *list);\end{verbatim}

    \description
    The intent of the \verb|list_verify| function is to perform a verification
    on the list object, regardless of whether the Kazlib implementation is
    operated in verification or production mode. If the list objects
    and its constituent nodes have been correctly manipulated, and the
    program has not caused any undefined behaviors, the value $1$ is returned.
    Otherwise, the function may be able to, but is not guaranteed to, detect
    corruption, and return the value zero.

\subsubsection{The {\tt lnode_borrow} function}

    \indexfunc{lnode_borrow}
    \synopsis
    \begin{verbatim}
    lnode_t *lnode_borrow(lnodepool_t *, void *);\end{verbatim}

    \description

    The \verb|lnode_borrow| function allocates a node from
    the pool managed by the given \verb|lnodepool_t| object.
    If the request succeeds, a pointer to the node is returned.  If the object
    has run out of nodes, the return value is a null pointer.

\subsubsection{The {\tt lnode_create} function}

    \indexfunc{lnode_create}
    \synopsis
    \begin{verbatim}
    lnode_t *lnode_create(void *);\end{verbatim}

    \description

    The \verb|lnode_create| function dynamically allocates a list node,
    stores in it the data value specified in the argument and
    returns a pointer to it. The allocation is performed by a call to the
    standard \verb|malloc| function. If the allocation fails, a null
    pointer is returned.

\subsubsection{The {\tt lnode_destroy} function}

    \indexfunc{lnode_destroy}
    \synopsis
    \begin{verbatim}
    void lnode_destroy(lnode_t *);\end{verbatim}

    \description

    The \verb|lnode_destroy| function destroys a list node that has been
    allocated with the \verb|lnode_create| function.  The value of any pointer
    that referred to the node that was thus freed is indeterminate.

    If the node is currently the occupant of a list, the behavior is undefined
    if the list is subsequently used.

\subsubsection{The {\tt lnode_get} function}

    \indexfunc{lnode_get}
    \synopsis
    \begin{verbatim}
    void *lnode_get(lnode_t *);\end{verbatim}

    \description

    The \verb|lnode_get| function retrieves the \verb|void *| data value
    associated with a node.\footnote{This is the {\bf only} interface for
    retrieving the data element.}
    
\subsubsection{The {\tt lnode_init} function}

    \indexfunc{lnode_init}
    \synopsis
    \begin{verbatim}
    lnode_t *lnode_init(lnode_t *, void *);\end{verbatim}

    The \verb|lnode_init| function initializes the contents
    of the specified list node object, assigning it the
    data value specified as the second argument. 
    The first argument is a pointer which refers to 
    a data object that has a suitable size and alignment
    for the representation of an \verb|lnode_t| type.
    After initialization with \verb|lnode_init|, the object is subsequently
    eligible as an operand to the functions of the List component.

\subsubsection{The {\tt lnode_is_in_a_list} function}

    \indexfunc{lnode_is_in_a_list}
    \synopsis
    \begin{verbatim}
    int lnode_is_in_a_list(lnode_t *);\end{verbatim}

    \description

    The \verb|lnode_is_in_a_list| function determines whether the given node is
    an occupant of some list. If the node is in a list, the function returns
    the value $1$.  If the node is not in any list, the return value is zero.

\subsubsection{The {\tt lnode_pool_create} function}

    \indexfunc{lnode_pool_create}
    \synopsis
    \begin{verbatim}
    lnodepool_t *lnode_pool_create(listcount_t);\end{verbatim}

    \constraints

    The value of the argument shall not be zero.

    \description

    The \verb|lnode_pool_create| function dynamically allocates,
    by means of the standard library function \verb|malloc|
    a node pool object containing the number of nodes specified
    as the first argument. If not enough resources are available,
    a null pointer is returned, otherwise a pointer to the
    \verb|lnodepool_t| object is returned.

\subsubsection{The {\tt lnode_pool_destroy} function}

    \indexfunc{lnode_pool_destroy}
    \synopsis
    \begin{verbatim}
    void lnode_pool_destroy(lnodepool_t *);\end{verbatim}

    \description

    The \verb|lnode_pool_destroy| function deallocates a
    node pool that was allocated by \verb|lnode_pool_create|.
    The value of any pointer which referred to the
    node pool object becomes indeterminate.

\subsubsection{The {\tt lnode_pool_init} function}

    \indexfunc{lnode_pool_init}
    \synopsis
    \begin{verbatim}
    lnodepool_t *lnode_pool_init(lnodepool_t *,
            lnode_t *, listcount_t);\end{verbatim}

    \constraints

    The third argument, which specifies the node count, shall not be zero.

    \description

    The \verb|lnode_pool_init| function initializes a data object
    that has a suitable size and alignment to represent an
    \verb|lnodepool_t| type. A pointer to this object is passed
    as the first argument. The node pool thus created draws nodes
    from an array specified by the second argument, which shall be a pointer to
    an object that can behave like an array of \verb|lnode_t| objects.
    The third argument specifies the number of elements in this array.

    After this function, the object pointed at by the \verb|lnodepool_t *|
    argument is eligible for use with the node pool management functions
    of the List component. Nodes may be drawn from the pool and returned to it.

    As long as the pool continues to be used, the program should not directly
    manipulate the node array. In particular, if the program modifies any
    part of the array, then the behavior is undefined if the
    \verb|lnodepool_t| object or any nodes drawn from it are subsequently
    passed to a List function. The program shall not directly use the array
    elements as independent \verb|lnode_t| objects while the array is
    associated with the pool; in particular, it shall not pass these elements
    to Kazlib functions that operate on \verb|lnode_t|.
    
    The behavior is undefined if the same array is associated with more than
    one node pool object, or if two node pool objects are given overlapping
    arrays.

    The node array is managed in an manner that is specific to the
    implementation; the intent is that each element of the array represents a
    distinct node object, a pointer to which can be returned in response to an
    allocation request.

    The \verb|lnode_pool_init| function returns a copy of the first argument.

\subsubsection{The {\tt lnode_pool_isempty} function}

    \indexfunc{lnode_pool_isempty}
    \synopsis
    \begin{verbatim}
    int lnode_pool_isempty(lnodepool_t *);\end{verbatim}

    \description

    The \verb|lnode_pool_isempty| function tests the 
    specified \verb|lnodepool_t| object for ability to supply nodes.
    If the object has been
    subject to so many requests that it is no longer capable of
    of supplying additional list nodes, the value $1$ is returned.
    Otherwise the return value returned is zero.

\subsubsection{The {\tt lnode_pool_isfrom} function}

    \indexfunc{lnode_pool_isfrom}
    \synopsis
    \begin{verbatim}
    int lnode_pool_isfrom(lnodepool_t *, lnode_t *);\end{verbatim}

    \description

    The function \verb|lnode_pool_isfrom|, intended to serve as a software
    verification aid, determines whether a list node originates from
    a particular node pool. The return value is $1$ if this relationship is
    true, otherwise zero.

\subsubsection{The {\tt lnode_put} function}

    \indexfunc{lnode_put}
    \synopsis
    \begin{verbatim}
    void lnode_put(lnode_t *, void *);\end{verbatim}

    \description

    The function \verb|lnode_put| replaces the data element
    associated with the list node. 

\subsubsection{The {\tt lnode_return} function}

    \indexfunc{lnode_return}
    \synopsis
    \begin{verbatim}
    void lnode_return(lnodepool_t *, lnode_t *);\end{verbatim}

    \constraints

    The node pointed at by the second argument was derived by an allocation
    request from the pool pointed at by the first argument.\footnote{In
    other words, the {\tt lnode_pool_isfrom} function, were it called with
    the same two arguments, would return $1$ if this constraint is met.}

    Furthermore, the node must not be the occupant of a list.

    \description

    The \verb|lnode_return| function returns a node back to the node pool from
    which it came. The node must not be subsequently used as an argument to any
    List functions, until it happens to be allocated again. The pointer to
    the node object remains valid, and may be returned by a subsequent
    allocation request from the same node pool.

\subsection{Implementation}
\index{List!reference implementation}

This section describes the elements of the reference implementation of the
List component. No requirement is imposed that an implementation should
follow the reference implementation. The same is true of the
implementation notes for the other components.

\subsubsection{Types}
\index{implementation!List types}
\index{typedefs!implementation of List}

The reference List implementation is a doubly-linked circular list
\index{sentinel node!of linked list}
with a {\it sentinel node}. The node structure type is defined like this:
\begin{verbatim}
    typedef struct lnode_t {
        struct lnode_t *list_next;
        struct lnode_t *list_prev;
        void *list_data;
    } lnode_t;
\end{verbatim}
and the list structure is defined like this:
\begin{verbatim}
    typedef struct list_t {
        lnode_t list_nilnode;
        listcount_t list_nodecount;
        listcount_t list_maxcount;
    } list_t;
\end{verbatim}
The \verb|list_nilnode| member of the list object is the sentinel. It is
always present in the list, never deleted. When the list is empty, the sentinel
node's \verb|list_next| and \verb|list_prev| pointers simply point back at the sentinel
node.  The \verb|list_maxcount| member of the list tells how many nodes may be
inserted and \verb|list_nodecount| keeps track of the actual count.

The reason the sentinel node is called \verb|list_nilnode| is that it
acts as the successor of a list's tail node, if there is one,
and as the predecessor of the first node.  In a linked list implementation
that does not use a sentinel node, the \verb|list_next| pointer of
the the tail node and the \verb|list_prev| pointer of the first node would
be null.

Note that prefixed names are used for all of the structure members.  This is so
that the header file conforms to the documented namespace. If, for example, the
\verb|list_nilnode| member were simply called \verb|nilnode|, then
if the program contained somewhere a macro called \verb|nilnode|, there would
be a potential clash. If the program defined \verb|nilnode| prior to including
the \verb|list.h| header, the declaration of \verb|struct list_t| would
be confounded. If the program defined \verb|nilnode| after 
including \verb|list.h|, the definition would interfere with \verb|list.h|
macros whose replacement text refers to the \verb|nilnode| member.

For programming convenience, the list implementation source file defines short
macro names for the structure members:
\begin{verbatim}
    #define next list_next
    #define prev list_prev
    #define data list_data
\end{verbatim}
... and so forth. These names are private to the translation unit, which
includes only standard ANSI C headers.  Some of the examples in this section
make use of the short names; it is assumed that these macros are in effect.

\subsubsection{Selected operations}
\index{implementation!List operations}

\paragraph{Retrieving the first node}
\index{List!first node}

Given a pointer \verb|P| to a \verb|list_t| type, the \verb|list_first|
function examines the value of \verb|P->nilnode.next| which points
at the head node if the list is not empty. If the list is empty,
then this expression points back at the sentinel node. In
other words, the comparison
\begin{verbatim}
    P->nilnode.next == &P->nilnode
\end{verbatim}
yields true when the list is empty. In this case, the interface requires that
a null pointer be returned by \verb|list_first|.  The implementation actually
uses the above test, through a test for \verb|P->nodecount| being equal to
zero is also possible.

In general, any operation which produces a pointer to the nilnode that must be
returned back to the calling program  must test for that case and return a null
pointer instead to satisfy the interface requirements.

\paragraph{Node deletion}
\index{List!deletion}

Thanks to the use of the sentinel node, the list deletion operation doesn't
have to test for special cases. A node in the middle of the list is
deleted in exactly the same way as the first or the last node:
\begin{verbatim}
    lnode_t *list_delete(list_t *list, lnode_t *del)
    {
        lnode_t *next = del->next;
        lnode_t *prev = del->prev;

        assert (list_contains(list, del));

        prev->next = next;
        next->prev = prev;
        list->nodecount--;

        del->next = del->prev = NULL;

        return del;
    }
\end{verbatim}
Quite simply, the successor and predecessor of the deleted node are connected
together so that the deleted node is spliced out from the list. If the node is
the last remaining one, then the sentinel node serves as both the successor and
the predecessor. The effect of the deletion then is to set the sentinel's next
and previous links to point to itself, as they did initially when the list was
previously empty.

The next and prev pointers are set to null not only for enhanced error checking
in language implementations that trap dereferences of null pointers,
but also to indicate that the node is not on any list. The interface
function \verb|lnode_is_in_a_list| makes use of this.

It's worth discussing in some detail why the values of expressions
\verb|del->next| and \verb|del->prev| are cached in local variables.  The
actual statements that splice the node out of the list could instead have been
written:
\begin{verbatim}
    del->prev->next = del->next;
    del->next->prev = del->prev;
\end{verbatim}
However, this causes some compilers to generate less than optimal code because
they fail to apply common subexpression elimination to the double
occurrence of \verb|del->next|.  Caching this expression in a local variable
helps to get better code by making the semantics more obvious.  In any case,
modern compilers tend to do a good job of caching locals in high speed storage,
particularly on architectures generously endowed with registers, so using a few
extra locals is unlikely to lead to worse target code. The principle of using
local variables to perform ``manual CSE'' is applied throughout the Kazlib
reference implementation.

\paragraph{Node insertion}
Node insertion is also simple, thanks to the sentinel node which makes
the doubly linked list circular. All insertions are done using
the functions \verb|list_ins_before| and \verb|list_ins_after|.
These are very similar, so it suffices to show \verb|list_ins_before|:
\begin{verbatim}
    void list_ins_before(list_t *list, lnode_t *new, lnode_t *this)
    {
        lnode_t *that = this->prev;

        assert (new != NULL);
        assert (!list_contains(list, new));
        assert (!lnode_is_in_a_list(new));
        assert (this == list_nil(list) || list_contains(list, this));
        assert (list->nodecount + 1 > list->nodecount);

        new->next = this;
        new->prev = that;
        that->next = new;
        this->prev = new;
        list->nodecount++;

        assert (list->nodecount <= list->maxcount);
    }
\end{verbatim}
The node \verb|this| is the one before which the new node is being
inserted. Internally, the pointer \verb|that| points to the
node after which the insertion takes place. In other words, the function
inserts the node \verb|new| in between \verb|this| and \verb|that|.

Note the copious assertions which verify all of the documented constraints:
that the node is not already on the list, or any other list, that the reference
node \verb|this| is in the list, and that the list capacity won't be exceeded,
and that the node count doesn't overflow its type.

\index{List!insertion}

\section{Hash component}

The Hash component provides a means to manage collections of elements, called
hashes, that are not ordered. Each element in the collection has a unique key,
which is used for searching and inserting. The intent is that the
implementation is based on extendible hashing, and the interface allows for
user-defined hashing functions. The number of elements that can be stored
in a hash is limited; maximum number of entries in a hash is known as its
{\it capacity}.

\subsection{Interface}

\subsubsection{The {\tt hash.h} header}

Each C or C++ translation unit that is to use the functionality of the Hash
component shall include the header \verb|hash.h|. This header shall
contain declarations of types and external functions, and definitions of
macros.  The following typedef names shall be
defined:\index{Hash!typedef names}
\index{typedefs!defined by Hash}
\begin{verbatim}
    hash_t                      hashcount_t
    hnode_t                     hash_val_t
    hash_comp_t                 hnode_alloc_t
    hscan_t                     hnode_free_t
    hash_fun_t
\end{verbatim}
In addition, the following structure tags may be defined:\index{Hash!tag names}
\index{tags!defined by Hash}
\begin{verbatim}
    struct hash_t
    struct hnode_t
    struct hscan_t
\end{verbatim}
The following external function names shall be declared:
\index{Hash!function names}\index{functions!defined by Hash}
\begin{verbatim}
    hash_create                 hash_count           
    hash_set_allocator          hash_size            
    hash_destroy                hash_isfull          
    hash_free_nodes             hash_isempty         
    hash_init                   hash_scan_begin      
    hash_insert                 hash_scan_next       
    hash_lookup                 hash_scan_delete     
    hash_delete                 hash_scan_delfree
    hash_alloc_insert           hash_verify          
    hash_delete_free            hnode_create         
    hnode_put                   hnode_init           
    hnode_get                   hnode_destroy        
    hnode_getkey                hash_free
\end{verbatim}
\index{Hash!external objects}
In addition, the external object name
\begin{verbatim}
    hash_val_t_bit
\end{verbatim}
shall be declared.  The following preprocessor symbols (macros) shall be
defined: \index{Hash!macro names}\index{macros!defined by Hash}
\indexmacro{HASHCOUNT_T_MAX}
\indexmacro{HASH_VAL_T_BIT}
\indexmacro{HASH_VAL_T_MAX}
\indexmacro{HASH_H}
\begin{verbatim}
    HASHCOUNT_T_MAX
    HASH_VAL_T_BIT
    HASH_H\end{verbatim}
\index{symbols!reserved by Hash}\index{Hash!reserved symbols}
Macro identifiers which begin with the upper-case prefix \verb|HASH| are
reserved for future extensions to the \verb|hash.h| header, as are
names in the ordinary and tag namespaces which begin with \verb|hash_|,
\verb|hnode_| or \verb|hscan_|. External names which begin with \verb|hash_|,
\verb|hnode_| or \verb|hscan_| are reserved by the Kazlib library regardless of
what headers are included.

\subsubsection{The {\tt hash_t} type}

\indextype{hash_t}
The type \verb|hash_t| is an opaque data type which maintains information about
the current state of a single hash.  From the programmer's viewpoint, a hash
consists of an instance of the \verb|hash_t| type, plus zero or more instances
of the type \verb|hnode_t|. An instance of the \verb|hash_t| type can be
dynamically created using the \verb|hash_create| function, and destroyed by the
\verb|hash_destroy| function.  Alternately, the program can declare an object
of type \verb|hash_t| and have it initialized via the \verb|hash_init|
function.  When initializing a hash this way, the user must also provide
a fixed-size array of \verb|hnode_t *| objects which serves as the hash table.
\footnote{A hash initialized this way does not support extendible hashing,
because there is no mechanism for growing the user-supplied array.}

\subsubsection{The {\tt hnode_t} type}

\indextype{hnode_t}
The \verb|hnode_t| type is an opaque type that represents a single element
that can be inserted into a hash. A hash node contains a a reference to
satellite data provided by the user.  Nodes may be dynamically created by the
\verb|hnode_create| function.  Alternately, the program may supply an
\verb|hnode_t| object that can be initialized by the \verb|hnode_init|
function. 

\subsubsection{The {\tt hash_comp_t} type}

\indextype{hash_comp_t}
The \verb|hash_comp_t| type is a typedef name for the pointer-to-function type
\begin{verbatim}
    int (*)(const void *, const void *);
\end{verbatim}
In the context of the Hash component, this type denotes pointers to
comparison functions.

\subsubsection{The {\tt hscan_t} type}

\indextype{hscan_t}
The \verb|hscan_t| typedef stands for an opaque type which represents
context information for traversing a hash. It is initialized by the
\verb|hash_scan_begin| function, which specifies a hash to be
traversed. Successive elements are retrieved using the \verb|hash_scan_next|
function, which eventually indicates that no more elements
remain. Inserting to, or deleting from a hash other than using
the function \verb|hash_scan_delete| causes any \verb|hscan_t|
objects that refer to it to become indeterminate.

\subsubsection{The {\tt hashcount_t} type}

\indextype{hashcount_t}
\indexmacro{HASHCOUNT_T_MAX}
This is an unsigned integral type which is capable of representing the number
of nodes in a hash. 
The \verb|HASHCOUNT_T_MAX| macro expands to a
constant expression of type \verb|hashcount_t| which specifies the maximum
value of that type.

\subsubsection{The {\tt hash_val_t} type}

\indextype{hash_val_t}
\indexmacro{HASH_VAL_T_MAX}
The \verb|hash_val_t| type is an unsigned integral type capable of
holding at least 32 bits. The purpose of this type is to represent the
output values of hashing functions.
The \verb|HASH_VAL_T_MAX| macro expands to a
constant expression of type \verb|hash_val_t| which specifies the maximum
value of that type.

\subsubsection{The {\tt hnode_alloc_t} type}

\index{Hash!allocator function}
The \verb|hnode_alloc_t| identifier is a typedef name for the pointer-to-function
type
\begin{verbatim}
    hnode_t *(*)(void *);
\end{verbatim}
In other words, a pointer to a function that takes a \verb|void *|
argument and returns a pointer to \verb|hnode_t|.
A function of this type which meets certain behavior criteria may be
registered with a \verb|hash_t| object as node allocator, together
with a compatible deallocator function. The \verb|void *| argument
passes user-specified context information through to the
allocator routines (see section \ref{section:hash_set_allocator}).

\subsubsection{The {\tt hnode_free_t} type}

\index{Hash!deallocator function}
The \verb|hnode_free_t| identifier is a typedef name for the
pointer-to-function type
\begin{verbatim}
    void (*)(hnode_t *, void *);
\end{verbatim}
A function of this type which meets certain behavior criteria may be
registered with a \verb|hash_t| object as node deallocator
together with a compatible allocator function.

\subsubsection{The {\tt hash_fun_t} type}

\index{hashing function}
The \verb|hash_fun_t| identifier is a typedef name for the
pointer-to-function type
\begin{verbatim}
    hash_val_t (*hash_fun_t)(const void *);
\end{verbatim}
A function of this type which behaves a certain way is called
a {\it hashing function}.  To be a viable hashing function, such
a function must take a pointer to a key object, and produce
an integer value that depends only on the contents of the key,
and possibly on information that does not change over the lifetime of any hash
for which that hashing function is used.  Additional requirements for hashing
functions are introduced later.

\subsubsection{The {\tt hash_val_t_bit} object}

    \indexobject{hash_val_t_bit}
    \synopsis
    \begin{verbatim}
    extern int hash_val_t_bit;\end{verbatim}

    \description

    The \verb|hash_val_t_bit| object of type int has a fixed value
    which counts the number of bits in the \verb|hash_val_t| object.
    The program shall not store a value into this object.
    
    The value of \verb|hash_val_t_bit| need not be correct until the
    first successful call to \verb|hash_create| or to \verb|hash_init|
    completes.

    The implementation shall provide the macro \verb|HASH_VAL_T_BIT| which
    expands to a non-lvalue expression that has the same value and type as the
    object, but which may be a constant expression.\footnote{The intent of
    providing these values is to ease the implementation of portable hashing
    functions that take advantage of all of the available bits of a given
    Kazlib implementation. Alternately, hashing functions may be constructed to
    only use the lower 32 bits of the type.}

\subsubsection{The {\tt hash_create} function}

    \indexfunc{hash_create}
    \index{Hash!creation of}
    \index{create!hash object}
    \synopsis
    \begin{verbatim}
    hash_t *hash_create(hashcount_t, hash_comp_t, hash_fun_t);\end{verbatim}

    \description

    If sufficient resources exist, the \verb|hash_create| function instantiates
    and initializes an object of type \verb|hash_t| and returns a pointer to
    it. Otherwise it returns a null pointer.

    The first argument establishes the capacity of the hash, which is
    initially empty.

    The second argument is a pointer to a comparison function that will be
    associated with the \verb|hash_t| object for its entire duration.

    \index{hashing function}
    The third argument is either null or a pointer to a hashing function
    that is permanently associated with the object. If it is null, a {\it default
    hashing function\/} is assigned by the implementation.

    The hashing function shall be invoked with an argument that is one
    of the keys that are being inserted into, or sought after, in the
    hash. The hashing function must produce the same value each time it
    is called for a given key. It is up to the hash user to define the
    representation of keys, to manage their storage, and to provide a matching
    hashing function.  The hash stores only generic \verb|void *| pointers to
    keys. 

    The default hashing function assumes that keys are null terminated
    strings. That is to say, it behaves as though its \verb|void *|
    argument points to the first elements of an array of \verb|unsigned|
    \verb|char|, the last of which is a null character. The use of
    the default hashing function with keys that do not have this representation
    results in undefined behavior.
    
\subsubsection{The {\tt hash_set_allocator} function}

    \indexfunc{hash_set_allocator}
    \label{section:hash_set_allocator}

    \synopsis
    \begin{verbatim}
    void hash_set_allocator(hash_t *, hnode_alloc_t,
            hnode_free_t, void *);\end{verbatim}

    \constraints

    The second and third arguments---the function pointers---shall either
    both be null, or both be non-null. The hash pointed at by the first
    argument shall be empty.

    \description

    When a hash is initialized, it is outfitted with a pair of default
    node allocation functions. These functions may be replaced with functions
    supplied by the program by calling the \verb|hash_set_allocator| function
    and specifying two suitable pointers. If these pointers are null, the
    default functions are restored.

    These functions are called to allocate and free \verb|hnode_t| 
    objects by the functions \verb|hash_alloc_insert|
    and \verb|hash_delete_free| (see sections
    \ref{section:hash_delete_free} and \ref{section:hash_alloc_insert}).

    If sufficient resources exist, the allocation function shall
    return a pointer to a unique storage object that is large enough
    and suitably aligned to represent an object of type \verb|dnode_t|.
    Otherwise, the function shall return a null pointer.

    The deallocation function shall be capable of disposing of the
    objects created by the matching allocator function.


\subsubsection{The {\tt hash_destroy} function}

    \indexfunc{hash_destroy}
    \synopsis
    \begin{verbatim}
    void hash_destroy(hash_t *);\end{verbatim}

    \constraints

    The hash pointed at by the first argument shall be empty.

    \description

    The \verb|hash_destroy| function deinitializes and deallocates a hash
    that was created with \verb|hash_create|.
    All pointers and \verb|hscan_t| objects that referred to the hash become
    indeterminate.

\subsubsection{The {\tt hash_free_nodes} function}

    \indexfunc{hash_free_nodes}
    \synopsis
    \begin{verbatim}
    void hash_free_nodes(hash_t *);\end{verbatim}

    \description

    The \verb|hash_free_nodes| function removes each node from
    the hash and destroys it as if by calling \verb|hash_delete_free|
    (Section \ref{section:hash_delete_free}). The order in which
    the nodes are destroyed is unspecified.

\subsubsection{The {\tt hash_free} function}

    \indexfunc{hash_free}
    \synopsis
    \begin{verbatim}
    void hash_free(hash_t *);\end{verbatim}

    \description

    Every node in the hash is removed from the hash and is then subject to the
    deallocation function. The overall effect is as if the function
    \verb|hash_delete_free| (Section \ref{section:hash_delete_free}) were
    invoked on each node, and then \verb|hash_destroy| invoked on the
    hash itself.

    This function is obsolescent, and will be removed from some future revision
    of this document.

\subsubsection{The {\tt hash_init} function}

    \indexfunc{hash_init}
    \synopsis
    \begin{verbatim}
    hash_t *hash_init(hash_t *, hashcount_t, hash_comp_t,
        hash_fun_t, hnode_t **, hashcount_t);
    \end{verbatim}

    \constraints

    The last argument, which specifies the size of the program-supplied table,
    shall be integral power of two that is greater than one---that is to say, an
    integer of the form $2^k$ where $k$ is a positive integer.
 
    \description
 
    The \verb|hash_init| function configures the specified \verb|hash_t| object
    to use a specified array of \verb|hnode_t *| pointer objects as a table.
    The user is responsible for providing storage for the \verb|hash_t|
    object and the array. As in the \verb|hash_create| interface,
    the second parameter specifies the capacity, and the subsequent
    arguments specify the comparison and hashing function, respectively.
    The last two arguments specify the table of pointers. The array object
    shall have at least as many elements as indicated by the last parameter,
    otherwise the behavior is undefined. The call to \verb|hash_init| is said
    to register the array with the hash.

    The program shall not register the same array with more than one hash.
    More specifically, once the program modifies a registered array, or
    registers it with another hash, it must discontinue use of the first hash.
    \footnote{Note that no explicit deinitialization function is provided to
    dissociate the array. A program disposes of a hash created by
    {\tt hash_init} by discontinuing its use.}
 
\subsubsection{The {\tt hash_insert} function}

    \indexfunc{hash_insert}
    \label{section:hash_insert}
    \synopsis
    \begin{verbatim}
    void hash_insert(hash_t *, hnode_t *, const void *);\end{verbatim}

    \constraints
    The hash is not full.  The key specified by the \verb|void *| parameter
    does not already exist in the specified hash. The node specified
    by the second parameter is not already inserted into a hash.

    \description
    The \verb|hash_insert| function adds a new node to a hash. The user
    must supply a node object that was initialized with \verb|hnode_init|
    or dynamically created with \verb|hnode_create|. If the node is
    already inserted into the same hash or any other hash, the behavior
    is undefined.

    A program may modify a key or node that has been inserted into a hash, or
    cause the storage of the key or the node to become invalid.  However, any
    subsequent use of the hash invokes undefined behavior, with the following
    exception: the data pointer stored within a node may be modified using the
    \verb|hnode_put| function.

    The \verb|hash_insert| function invokes the hashing function callback with
    the key pointer as the argument.

    The \verb|hash_insert| function may need to acquire additional storage in
    order to support hash table growth. If the storage allocation fails, the
    function shall fully recover, and insert the node without growing the
    table.

    The Hash implementation shall not modify the storage referenced by a key,
    and shall not access it other than indirectly through the supplied hashing
    and comparison functions.

\subsubsection{The {\tt hash_lookup} function}

    \indexfunc{hash_lookup}
    \synopsis
    \begin{verbatim}
    hnode_t *hash_lookup(hash_t *, const void *);\end{verbatim}

    \description

    The \verb|hash_lookup| function searches the given hash for a node
    matching the given key. Unless the hash is empty, the key shall be
    compared against one or more keys that are already in the hash,
    using the comparison function. The key pointer may
    be identical to one that has already been inserted into the
    hash.\footnote {In that case, the comparison function must correctly
    cope with aliased parameters}.

    If the key is found in the hash, a pointer to the corresponding node
    is returned.\footnote{The corresponding node is the one that was specified
    in the call to {\tt hash_insert} together with the matching key.}

    If the key is not found, a null pointer is returned.

\subsubsection{The {\tt hash_delete} function}

    \indexfunc{hash_delete}
    \synopsis
    \begin{verbatim}
    hnode_t *hash_delete(hash_t *, hnode_t *);\end{verbatim}

    \constraints
    The specified node is an occupant of the given hash.

    \description
    The \verb|hash_delete| function removes from the given hash a
    node that has previously been inserted into it. The key under
    which the node was inserted is also removed from the hash.\footnote{Thus
    the program may arbitrarily manipulate the removed key without destroying
    the integrity of the hash.}

    Any existing \verb|hscan_t| iterator which is associated with the
    hash becomes indeterminate.\footnote{To delete the current node during hash
    table traversal, the {\tt hash_scan_delete} function must be used
    instead.}


\subsubsection{The {\tt hash_alloc_insert} function}

    \label{section:hash_alloc_insert}
    \indexfunc{hash_alloc_insert}

    \synopsis
    \begin{verbatim}
    int hash_alloc_insert(hash_t *, const void *, void *);\end{verbatim}

    \constraints

    The second argument specifies the insertion key. The hash shall not
    already contain this key.

    \description

    The \verb|hash_alloc_insert| function dynamically allocates and
    initializes a \verb|hnode_t| object and inserts it into the 
    given hash. The second argument and third arguments are pointers
    to user data and key objects, either of which may be null.

    The allocation is performed by a call to the default allocation
    function, or to the function that was configured using
    \verb|hash_set_allocator| (Section \ref{section:hash_set_allocator}).

    If the allocation succeeds, the insertion is performed and
    the value 1 is returned.  If the allocation fails, no insertion is
    performed and 0 is returned.

\subsubsection{The {\tt hash_delete_free} function}

    \label{section:hash_delete_free}
    \indexfunc{hash_delete_free}

    \synopsis
    \begin{verbatim}
    void hash_delete_free(hash_t *, hnode_t *)
    \end{verbatim}

    \constraints
    The given node can be found within the given hash.
   
    \description
    The \verb|hash_delete_free| function is the reverse of
    \verb|hash_alloc_insert|. It removes the given node form the
    hash as if by a call to \verb|hash_delete| and then deletes it using the
    default or user-defined allocator (Section
    \ref{section:hash_set_allocator}). If the given node had not been created
    using \verb|hash_alloc_insert|, the behavior is undefined.

\subsubsection{The {\tt hnode_put} function}

    \indexfunc{hnode_put}
    \synopsis
    \begin{verbatim}
    void hnode_put(hnode_t *, void *);\end{verbatim}

    \description
    The function \verb|hnode_put| replaces the data element
    associated with the hash node.

\subsubsection{The {\tt hnode_get} function}

    \indexfunc{hnode_get}
    \synopsis
    \begin{verbatim}
    void *hnode_get(hnode_t *);\end{verbatim}

    \description
    The \verb|hnode_get| function retrieves the \verb|void * | data value
    associated with the given hash node.

\subsubsection{The {\tt hnode_getkey} function}

    \indexfunc{hnode_getkey}
    \synopsis
    \begin{verbatim}
    const void *hnode_getkey(hnode_t *);\end{verbatim}

    \description

    The \verb|hnode_getkey| function retrieves the \verb|void *| key value 
    associated with the given node. A node acquires an associated key
    when it is inserted into a hash (see section \ref{section:hash_insert}).
    Invoking \verb|hnode_getkey| on a node that has not been inserted
    into a hash results in undefined behavior.

\subsubsection{The {\tt hash_count} function}

    \indexfunc{hash_count}
    \synopsis
    \begin{verbatim}
    hashcount_t hash_count(hash_t *);\end{verbatim}

    \description
    The \verb|hash_count| function returns a value which represents the number
    of nodes currently stored in the hash pointed at by the argument.

\subsubsection{The {\tt hash_size} function}

    \indexfunc{hash_size}
    \synopsis
    \begin{verbatim}
    hashcount_t hash_size(hash_t *hash)\end{verbatim}

    \description
    The \verb|hash_size| function returns an implementation-defined value that
    depends on the number of entries in the given hash.  The intent is that the
    value represent the size of the internal hash table managed by the given
    hash.

\subsubsection{The {\tt hash_isfull} function}

    \indexfunc{hash_isfull}
    \synopsis
    \begin{verbatim}
    int hash_isfull(hash_t *);\end{verbatim}

    \description
    The \verb|hash_isfull| function returns 1 if the hash is full,
    otherwise it returns 0.

    If the argument is an expression with side effects, the behavior is
    undefined.\index{macros!and side effects}


\subsubsection{The {\tt hash_isempty} function}

    \indexfunc{hash_isempty}
    \synopsis
    \begin{verbatim}
    int hash_isempty(hash_t *);\end{verbatim}

    \description
    The \verb|hash_isempty| function returns 1 if the given hash is empty,
    otherwise it returns 0.

\subsubsection{The {\tt hash_scan_begin} function}

    \indexfunc{hash_scan_begin}
    \synopsis
    \begin{verbatim}
    void hash_scan_begin(hscan_t *, hash_t *);\end{verbatim}

    \description
    The \verb|hash_scan_begin| initializes the \verb|hscan_t| iterator object,
    preparing it for a traversal of the given hash.

    After this initialization, if the hash is modified in any way by
    the performance of an insertion or deletion operation, the
    value of the \verb|hscan_t| object becomes indeterminate,
    with one exception:  the \verb|hash_scan_delete| function or the
    \verb|hash_scan_delfree| function may be used to delete the current
    node.

\subsubsection{The {\tt hash_scan_next} function}

    \indexfunc{hash_scan_next}
    \synopsis
    \begin{verbatim}
    hnode_t *hash_scan_next(hscan_t *);\end{verbatim}

    \description
    If any unvisited nodes remain, the \verb|hash_scan_next| function advances
    to the next one and returns a pointer to it. Otherwise, it returns a null
    pointer. Repeated invocations of \verb|hash_scan_next| return a pointer to
    every node that has been inserted into the table, in no particular order,
    such that no node is reported twice.

\subsubsection{The {\tt hash_scan_delete} function}

    \indexfunc{hash_scan_delete}
    \synopsis
    \begin{verbatim}
    hnode_t *hash_scan_delete(hash_t *, hnode_t *);
    \end{verbatim}

    \constraints
    The specified node is an occupant of the given hash.

    \description
    This function is almost exactly like \verb|hash_delete| except that it may
    be used to delete a node that has been most recently obtained from
    \verb|hash_scan_next| without destroying the validity of the \verb|hscan_t|
    iterator from which the node was obtained.

\subsubsection{The {\tt hash_scan_delfree} function}

    \label{section:hash_scan_delfree}
    \indexfunc{hash_scan_delfree}

    \synopsis
    \begin{verbatim}
    void hash_scan_delfree(hash_t *, hnode_t *)
    \end{verbatim}

    \constraints
    The given node can be found within the given hash.
   
    \description
    The \verb|hash_scan_delfree| function is similar to
    \verb|hash_delete_free|. It removes the given node form the
    hash and then deletes it using the default or user-defined allocator
    (Section \ref{section:hash_set_allocator}). If the given node
    had not been created using \verb|hash_alloc_insert|, the behavior
    is undefined.

    The deletion from the hash is performed as if by a call to
    \verb|hash_scan_delete|, thus it is safe to delete a node that
    was most recently obtained from a \verb|hash_scan_next| without
    destroying the validity of the \verb|hscan_t| iterator.

\subsubsection{The {\tt hash_verify} function}

    \indexfunc{hash_verify}
    \synopsis
    \begin{verbatim}
    int hash_verify(hash_t *hash);\end{verbatim}

    \description
    The intent of the \verb|hash_verify| function is to perform a verification
    on the hash object, regardless of whether the Kazlib implementation is
    operated in verification or production mode. If the hash object
    and its constituent nodes have been correctly manipulated, and the
    program has not caused any undefined behaviors, the value $1$ is returned.
    Otherwise, the function may be able to, but is not guaranteed to, detect
    corruption, and return the value zero.

\subsubsection{The {\tt hnode_create} function}

    \indexfunc{hnode_create}
    \synopsis
    \begin{verbatim}
    hnode_t *hnode_create(void *);\end{verbatim}

    \description
    The \verb|hnode_create| function dynamically allocates a hash node,
    stores in it the data value specified in the argument and
    returns a pointer to it. The allocation is performed by a call to the
    standard \verb|malloc| function. If the allocation fails, a null
    pointer is returned.

    The node's key pointer remains indeterminate until it is the subject of a
    \verb|hash_insert| operation.

\subsubsection{The {\tt hnode_init} function}

    \indexfunc{hnode_init}
    \synopsis
    \begin{verbatim}
    hnode_t *hnode_init(hnode_t *, void *);\end{verbatim}

    \description
    The \verb|hnode_init| function initializes the contents
    of the specified hash node object, assigning it the
    data value specified as the second argument. 
    The first argument is a pointer which refers to 
    a data object that has a suitable size and alignment
    for the representation of an \verb|hnode_t| type.
    After initialization with \verb|hnode_init|, the object is subsequently
    eligible as an operand to the functions of the hash component,
    other than \verb|hnode_getkey|.

    The node's key pointer remains indeterminate until it is the subject of a
    \verb|hash_insert| operation.

\subsubsection{The {\tt hnode_destroy} function}

    \indexfunc{hnode_destroy}
    \synopsis
    \begin{verbatim}
    void hnode_destroy(hnode_t *);\end{verbatim}

    \description
    The \verb|hnode_destroy| function destroys a hash node that has been
    allocated with the \verb|hnode_create| function.  The value of any pointer
    that referred to the node that was thus freed is indeterminate.

    If the node is currently the occupant of a hash, the behavior is undefined
    if the hash is subsequently used.

\subsection{Implementation}

TODO

\section{Dictionary component}

\index{Dictionary}
The Dictionary component provides a means to manage ordered sequences of
elements, having the following properties:
\begin{enumerate}
\item If the dictionary is not empty, a first and last element can be identified.
    In a dictionary having only one element, that one element is both the first and
    last element.
\item Each element that is not the last element has another element as its
    {\it successor}.
    \index{successor!of a dictionary element}
    \index{Dictionary!successor of an element}
\item Each element that is not the first element has a {\it predecessor}.
    \index{predecessor!of a dictionary element}
    \index{Dictionary!predecessor of an element}
\item No element is the predecessor or successor of more than one element.
\item If one element is the successor of another, the other is necessarily the
    predecessor of the first.
\item Each element is associated with a piece of information known as 
    the key. The sequence is ordered according to the relation imposed
    by the comparison function: the key of an element compares
    greater than or equal to the key of its predecessor.
\item If duplicate keys are present, then elements
    having the same key form a subsequence with no other keys in it, which
    follows from the previous property. No additional ordering is imposed
    within such subsequences.
\item Each element is associated with arbitrary satellite data.
\end{enumerate}

The Dictionary component supports efficient operations over such ordered
sequences: such as insertion, deletion, ordered traversal, as well as exact and
range searches.\footnote{The implicit association of keys and satellite data,
together with the ability of efficiently search by key to retrieve data, gives
rise to the term {\it dictionary}. A dictionary need not be ordered; a hash can
therefore also be considered to be a kind of dictionary; the Kazlib
nomenclature is somewhat unfortunate in that regard.}

The number of elements that can be stored in a dictionary is limited; maximum
number of entries in a dictionary is known as its {\it capacity}.

\subsection{Interface}

\subsubsection{The {\tt dict.h} header}

Each C or C++ translation unit that is to use the functionality of the Dict
component shall include the header \verb|dict.h|. This header shall
contain declarations of types and external functions, and definitions of
macros.  The following typedef names shall be
defined:\index{Dict!typedef names}
\index{typedefs!defined by Dict}
\begin{verbatim}
    dict_t                      dnode_process_t
    dnode_t                     dnode_alloc_t
    dictcount_t                 dnode_free_t
    dict_comp_t                 dict_load_t
\end{verbatim}
In addition, the following structure tags may be defined:\index{Dict!tag names}
\index{tags!defined by Dict}
\begin{verbatim}
    struct dict_t
    struct dnode_t
\end{verbatim}
The following external function names shall be declared:
\index{Dict!function names}\index{functions!defined by Dict}
\begin{verbatim}
    dict_create                 dict_count                     
    dict_set_allocator          dict_isempty                   
    dict_destroy                dict_isfull                    
    dict_free_nodes             dict_contains                  
    dict_init                   dict_allow_dupes               
    dict_verify                 dnode_is_in_a_dict             
    dict_lookup                 dnode_create                   
    dict_lower_bound            dnode_init                     
    dict_upper_bound            dnode_destroy                  
    dict_insert                 dnode_get                      
    dict_delete                 dnode_getkey                   
    dict_alloc_insert           dnode_put                      
    dict_delete_free            dict_process                   
    dict_first                  dict_load_begin
    dict_last                   dict_load_next
    dict_next                   dict_load_end 
    dict_prev                   dict_free
\end{verbatim}
The following preprocessor symbols shall be
defined: \index{Dict!macro names}\index{macros!defined by Dict}
\indexmacro{DICTCOUNT_T_MAX}
\indexmacro{DICT_H}
\begin{verbatim}
    DICTCOUNT_T_MAX
    DICT_H\end{verbatim}
\index{symbols!reserved by Dict}\index{Dict!reserved symbols}
Macro identifiers which begin with the upper-case prefix \verb|DICT| are
reserved for future extensions to the \verb|dict.h| header, as are
names in the ordinary and tag namespaces which begin with \verb|dict_|
or \verb|dnode_|. External names which begin with \verb|dict_|
or \verb|dnode_| are reserved by the Kazlib library regardless of
what headers are included.

\subsubsection{The {\tt dict_t} type}

\indextype{dict_t}
The type \verb|dict_t| is an opaque data type which represents a single
dictionary. A dictionary consists of an instance of the \verb|dict_t| type,
plus zero or more instances of the type \verb|dnode_t|. An object of type
\verb|dict_t| can be initialized by the \verb|dict_init| function. Alternately,
the \verb|dict_create| function will dynamically allocate and initialize a
dictionary.  An empty dictionary created by \verb|dict_create| may be disposed
of using \verb|dict_destroy|.

\subsubsection{The {\tt dnode_t} type}

\indextype{dnode_t}
The \verb|dnode_t| type represents a single entry in a dictionary called a
dictionary node.  The object stores a pointer to user data, and a key pointer
that is assigned to the dictionary node at the time when it is inserted into
the dictionary. A \verb|dnode_t| may be dynamically created using
\verb|dnode_create| and destroyed using \verb|dnode_destroy|. Alternately,
the program may supply storage for a \verb|dnode_t| object and initialize
it using the \verb|dnode_init| function.

\subsubsection{The {\tt dictcount_t} type}

\indextype{dictcount_t}
\indexmacro{DICTCOUNT_T_MAX}
This is an unsigned integral type which is capable of representing the number
of nodes in a dictionary.  The \verb|DICTCOUNT_T_MAX| macro expands to a
constant expression of type \verb|dictcount_t| which specifies the maximum
value of that type.

\subsubsection{The {\tt dict_comp_t} type}

\indextype{dict_comp_t}
The \verb|dict_comp_t| type is a typedef name for the pointer-to-function type
\begin{verbatim}
    int (*)(const void *, const void *);
\end{verbatim}
In the context of the Dictionary component, this type denotes pointers to
comparison functions. 

\subsubsection{The {\tt dnode_process_t} type}

\indextype{dnode_process_t}
The type \verb|dnode_process_t| is a typedef name for the pointer-to-function type
\begin{verbatim}
    void (*)(dict_t *, dnode_t *, void *);
\end{verbatim}
In the context of the Dictionary component, this is the type of a
dictionary node processing function (See section \ref{section:dict_process}).
The first two parameters identify a dictionary and the node within that
dictionary that is being processed. The third argument is a context pointer.

\subsubsection{The {\tt dnode_alloc_t} type}

\indextype{dnode_alloc_t}
The type \verb|dnode_alloc_t| is a typedef name for the pointer-to-function type
\begin{verbatim}
    dnode_t *(*)(void *);
\end{verbatim}
A function compatible with this type which meets certain other criteria may be
registered with a \verb|dict_t| object as a node allocator function
(See section \ref{section:dict_set_allocator}).

\subsubsection{The {\tt dnode_free_t} type}

\indextype{dnode_free_t}
The type \verb|dnode_free_t| is a typedef name for the pointer-to-function type
\begin{verbatim}
    void (*)(dnode_t *, void *);
\end{verbatim}
A function compatible with this type which meets certain other criteria may be
registered with a \verb|dict_t| object as a node deallocator function.
(See section \ref{section:dict_set_allocator}).

\subsubsection{The {\tt dict_load_t} type}

\indextype{dict_load_t}

The \verb|dict_load_t| type is opaque, and represents a context structure
used during the process of constructing a dictionary from an ordered list
of nodes.  (See sections \ref{section:dict_load_begin} to
\ref{section:dict_load_end}).

\subsubsection{The {\tt dict_create} function}

    \indexfunc{dict_create}
    \index{Dictionary!creation of}
    \index{create!dictionary object}

    \synopsis
    \begin{verbatim}
    dict_t *dict_create(dictcount_t, dict_comp_t);\end{verbatim}

    \description
    The \verb|dict_create| function allocates a new
    object of type \verb|dict_t| and initializes it to act as
    a dictionary.
    
    If insufficient resources exist for the allocation,
    a null pointer is returned, otherwise a pointer to the dictionary
    is returned.
    
    The first argument specifies the capacity of the dictionary,
    which is initially empty.

    The second argument is a comparison function that is used for comparing
    keys during insertion and searching operations, and is associated
    with the dictionary for its entire duration.

\subsubsection{The {\tt dict_set_allocator} function}

    \label{section:dict_set_allocator}
    \indexfunc{dict_set_allocator}

    \synopsis
    \begin{verbatim}
    void dict_set_allocator(dict_t *, dnode_alloc_t,
            dnode_free_t, void *);\end{verbatim}

    \constraints

    The second and third arguments---the function pointers---shall either
    both be null, or both be non-null. The dictionary pointed at by the first
    argument shall be empty.

    \description

    When a dictionary is initialized, it is outfitted with a pair of default
    node allocation functions. These functions may be replaced with functions
    supplied by the program by calling the \verb|dict_set_allocator| function
    and specifying two suitable pointers. If these pointers are null, the
    default functions are restored.

    These functions are called to allocate and free \verb|dnode_t|
    objects by the functions \verb|dict_alloc_insert|
    and \verb|dict_delete_free| (see sections
    \ref{section:dict_delete_free} and \ref{section:dict_alloc_insert}).

    If sufficient resources exist, the allocation function shall
    return a pointer to a unique storage object that is large enough
    and suitably aligned to represent an object of type \verb|dnode_t|.
    Otherwise, the function shall return a null pointer.

    The deallocation function shall be capable of disposing of the
    objects created by the matching allocator function.

\subsubsection{The {\tt dict_destroy} function}

    \indexfunc{dict_destroy}

    \synopsis
    \begin{verbatim}
    void dict_destroy(dict_t *);\end{verbatim}

    \constraints

    The dictionary pointed at by the first argument shall be empty.

    \description

    The \verb|dict_destroy| function deinitializes and deallocates a dictionary
    object that was created by \verb|dict_create|.  All pointers that
    referred to the dictionary become indeterminate.

\subsubsection{The {\tt dict_free_nodes} function}

    \indexfunc{dict_free_nodes}

    \synopsis
    \begin{verbatim}
    void dict_free_nodes(dict_t *);\end{verbatim}

    \description

    Every node in the dictionary is removed from the dictionary and is then
    subject to the deallocation function, as if the function
    \verb|dict_delete_free| (Section \ref{section:dict_delete_free}) were
    invoked on each node, in some unspecified order.

\subsubsection{The {\tt dict_free} function}

    \indexfunc{dict_free}

    \synopsis
    \begin{verbatim}
    void dict_free(dict_t *);\end{verbatim}

    \description

    This function is obsolescent, and will be removed from some future revision
    of this document. It is equivalent to \verb|dict_free_nodes|.

\subsubsection{The {\tt dict_init} function}

    \indexfunc{dict_init}

    \synopsis
    \begin{verbatim}
    dict_t *dict_init(dict_t *, dictcount_t, dict_comp_t);\end{verbatim}

    \description
 
    The \verb|dict_init| function prepares specified \verb|dict_t| object
    to behave as a dictionary that may subsequently be used with the other
    dictionary functions.
    
    The first argument points to the \verb|dict_t| object to be initialized.
    The second argument specifies the capacity of the dictionary. The third
    argument is a pointer to the comparison function which shall be associated
    with the dictionary for its entire duration.

\subsubsection{The {\tt dict_verify} function}

    \indexfunc{dict_verify}

    \synopsis
    \begin{verbatim}
    int dict_verify(dict_t *);\end{verbatim}

    \description

    The intent of the \verb|dict_verify| function is to perform a verification
    on the dictionary object, regardless of whether the Kazlib implementation
    is operated in verification or production mode. If the dictionary object
    and its constituent nodes have been correctly manipulated, and the program
    has not caused any undefined behaviors, the value $1$ is returned.
    Otherwise, the function may be able to, but is not guaranteed to, detect
    corruption, and return the value zero.

\subsubsection{The {\tt dict_lookup} function}

    \indexfunc{dict_lookup}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_lookup(dict_t *, const void *);\end{verbatim}

    \description
    The \verb|dict_lookup| function searches the given dictionary for a node
    matching the given key. Unless the dictionary is empty, the key shall be
    compared against one or more keys that are already in the dictionary, using
    the comparison function. The key pointer may be identical to one that has
    already been inserted into the dictionary.

    If the key is found in the dictionary, a pointer to the corresponding node
    is returned.

    If the key is not found, a null pointer is returned.

    If the dictionary contains more than one key which matches the search
    key, then the first key in the subsequence of duplicate keys is returned.

\subsubsection{The {\tt dict_lower_bound} function}

    \indexfunc{dict_lower_bound}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_lower_bound(dict_t *, const void *);\end{verbatim}

    \description

    The \verb|dict_lower_bound| function searches the dictionary in a manner
    similar to \verb|dict_lookup|.
    
    If the given key exists in the dictionary, the behavior is exactly the same
    as \verb|dict_lookup|.
    
    However, if the key is not found, then the node which has the smallest key
    that is greater than the search key is returned. If no such key exists
    (because the search key is higher than any other key in the dictionary
    or the dictionary is empty) then a null pointer is returned.

    \example
    Suppose that pointer \verb|d| refers to a dictionary whose registered
    comparison function performs lexicographic comparisons on ordinary
    C strings, similar to \verb|strcmp|.  To iterate over all keys that
    begin with the letter \verb|d|, the following idiom can be used:
    \begin{verbatim}
    dict_t *d;
    dnode_t *n, *start, *end;
    /*...*/
    start = dict_lower_bound(d, "d");
    end = dict_lower_bound(d, "e");
    for (n = start; n != end; n = dict_next(d, n)) {
        /* n points to each node in turn whose
           key starts with 'd' */
    }
    \end{verbatim}
    Note that if the dictionary is empty, or has keys which are all lower
    than \verb|"d"|, then both \verb|start| and \verb|end| shall be null
    pointers, and the loop body will never execute since the two are equal.
    Also note that if there are keys that begin with \verb|d| and the
    dictionary's last node has a key that starts with \verb|d|, then \verb|end|
    is null, otherwise \verb|end| points to the first key that doesn't begin
    with \verb|d|. In both cases, the loop will terminate after processing the
    last \verb|d| key, because \verb|dict_next| shall produce a pointer that is
    equal to \verb|end|.

\subsubsection{The {\tt dict_upper_bound} function}

    \indexfunc{dict_upper_bound}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_upper_bound(dict_t *, const void *);\end{verbatim}

    \description

    The \verb|dict_upper_bound| function searches the dictionary in a manner
    similar to \verb|dict_lookup|.
    
    If the given key exists in the dictionary, the behavior is exactly the same
    as \verb|dict_lookup| with one difference: 
    If the dictionary contains more than one key which matches the search
    key, then the last key in the sequence of duplicates is returned,
    rather than the first.
    
    However, if the key is not found, then the node which has the greatest key
    that is lower than the search key is returned. If no such key exists
    (because the search key is lower than any other key in the dictionary
    or the dictionary is empty) then a null pointer is returned.
  
    \example
    The following idiom can be used to iterate over a sequence of duplicate
    keys without the overhead of performing a full comparison before each
    iteration to detect the first non-matching key. 
    \begin{verbatim}
    dict_t *d;
    void *key;
    dnode_t *n, *start, *end;

    /* ... Initialize d, and key. ...*/
    start = dict_lower_bound(d, key);
    end = dict_upper_bound(d, key);

    /* advance end to first non-matching key */
    if (end != 0)
        end = dict_next(d, end);
    else
        end = start;	/* start == dict_first(d) in this case */

    for (n = start; n != end; n = dict_next(d, n)) {
        /* n points to duplicate keys in turn */
    }
    \end{verbatim}
    Immediately prior to the execution of the if statement, exactly one of the
    following conditions is true:
    \begin{itemize}
    \item The key was found in the dictionary; \verb|start| points to the
	first duplicate node and \verb|end| points to the last.
    \item The dictionary has only higher keys than the search key; \verb|start|
	points to the first node in the dictionary and \verb|end| is null.
    \item The dictionary has only lower keys than the search key; \verb|end|
	points to the last node in the dictionary, and \verb|start| is null.
    \item The dictionary has both lower and higher keys; \verb|end| and \verb|start|
	point to two consecutive nodes, respectively, such that the node
	pointed at by \verb|end| has a lower key than the search key and
	the node pointed at by \verb|start| has a higher key.
    \item The dictionary is empty; \verb|start| and \verb|end| are null.
    \end{itemize}
    The if statement ensures that if the dictionary contains no matching
    keys, than \verb|start| and \verb|end| are equal, and if the dictionary
    contains one or more matching keys, than \verb|end| points to the first
    non-matching node, or is null if there is no such node.  Thus the loop
    performs correctly in all circumstances.

\subsubsection{The {\tt dict_insert} function}

    \label{section:dict_insert}
    \indexfunc{dict_insert}

    \synopsis
    \begin{verbatim}
    void dict_insert(dict_t *, dnode_t *, const void *);\end{verbatim}

    \constraints
    The dictionary is not full.  If the dictionary has not been configured
    to allow duplicate keys, the key specified by the \verb|void *| parameter
    does not already exist in the dictionary.

    \description
    The \verb|dict_insert| function adds a new node to a dictionary. The user
    must supply a node object that was initialized with \verb|dnode_init| or
    dynamically created with \verb|dnode_create|. If the node is already
    inserted into the same dictionary or any other dictionary, the behavior is
    undefined.

    Duplicate keys may be inserted into a dictionary only if the dictionary
    has been configured to permit duplicate keys (see section
    \ref{section:dict_allow_dupes}). If this is the case, it is also
    permissible to insert the same key more than once: the implementation shall
    not distinguish between distinct keys that are declared equal by a
    correctly designed comparison function, and two key pointers that refer to
    the same key.

    A program may modify a key or node that has been inserted into a
    dictionary, or cause the storage of the key or the node to become invalid.
    However, any subsequent use of the dictionary invokes undefined behavior, with
    the following exception: the data pointer stored within a node may be
    modified using the \verb|dnode_put| function.

    The Dictionary implementation shall not modify the storage referenced by a
    key, and shall not access it other than indirectly through the supplied
    comparison function.

\subsubsection{The {\tt dict_delete} function}

    \indexfunc{dict_delete}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_delete(dict_t *, dnode_t *);\end{verbatim}

    \constraints
    The specified node is an occupant of the given dictionary.

    \description
    The \verb|dict_delete| function removes from the given dictionary a
    node that has previously been inserted into it. The key under
    which the node was inserted is also removed from the dictionary.

\subsubsection{The {\tt dict_alloc_insert} function}

    \label{section:dict_alloc_insert}
    \indexfunc{dict_alloc_insert}

    \synopsis
    \begin{verbatim}
    int dict_alloc_insert(dict_t *, const void *, void *);\end{verbatim}

    \constraints

    The second argument specifies the insertion key. The dictionary shall not
    already contain this key unless it has been configured as allowing
    duplicates.

    \description

    The \verb|dict_alloc_insert| function dynamically allocates and
    initializes a \verb|dnode_t| object and inserts it into the 
    given dictionary. The second argument and third arguments are pointers
    to user data and key objects, either of which may be null.

    The allocation is performed by a call to the default allocation
    function, or to the function that was configured using
    \verb|dict_set_allocator| (Section \ref{section:dict_set_allocator}).

    If the allocation succeeds, the insertion is performed and
    the value 1 is returned.  If the allocation fails, no insertion is
    performed and 0 is returned.

\subsubsection{The {\tt dict_delete_free} function}

    \label{section:dict_delete_free}
    \indexfunc{dict_delete_free}

    \synopsis
    \begin{verbatim}
    void dict_delete_free(dict_t *, dnode_t *);\end{verbatim}

    \constraints
    The given node can be found within the given dictionary.
   
    \description
    The \verb|dict_delete_free| function is the reverse of
    \verb|dict_alloc_insert|. It removes the given node form the
    dictionary and then deletes it using the default or user-defined allocator
    (Section \ref{section:dict_set_allocator}). If the given node
    had not been created using \verb|dict_alloc_insert|, the behavior
    is undefined.

\subsubsection{The {\tt dict_first} function}

    \indexfunc{dict_first}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_first(dict_t *);\end{verbatim}

    \description
    If the dictionary pointed at by the argument is empty, a null pointer
    is returned. Otherwise, a pointer to the first node in that dictionary is
    returned. 

\subsubsection{The {\tt dict_last} function}

    \indexfunc{dict_last}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_last(dict_t *);\end{verbatim}

    \description
    If the dictionary pointed at by the argument is empty, a null pointer
    is returned. Otherwise, a pointer to the last node in that dictionary is
    returned. 


\subsubsection{The {\tt dict_next} function}

    \indexfunc{dict_next}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_next(dict_t *, dnode_t *);\end{verbatim}

    \constraints
    The node pointed at by the second argument is an occupant of the dictionary
    pointed at by the first argument.

    \description
    If the node pointed at by the second argument has a successor, a pointer to
    that successor is returned. Otherwise, a null pointer is returned.

    \example
    The \verb|dict_first| and \verb|dict_next| functions can be used together
    to iterate over all of the elements of the dictionary, as in the following
    idiom:
    \begin{verbatim}
    dict_t *d;
    dnode_t *n;
    /*...*/
    for (n = dict_first(d); n != 0; n = dict_next(d, n)) {
        /* n points to each node in turn */
    }
    \end{verbatim}

\subsubsection{The {\tt dict_prev} function}

    \indexfunc{dict_prev}

    \synopsis
    \begin{verbatim}
    dnode_t *dict_prev(dict_t *, dnode_t *);\end{verbatim}

    \constraints
    The node pointed at by the second argument is an occupant of the dictionary
    pointed at by the first argument.

    \description
    If the node pointed at by the second argument has a predecessor, a pointer
    to that predecessor is returned. Otherwise, a null pointer is returned.

\subsubsection{The {\tt dict_count} function}

    \indexfunc{dict_count}

    \synopsis
    \begin{verbatim}
    dictcount_t dict_count(dict_t *);\end{verbatim}

    \description
    The \verb|dict_count| function returns a value which represents the number
    of nodes currently stored in the dictionary pointed at by the argument.

\subsubsection{The {\tt dict_isempty} function}

    \indexfunc{dict_isempty}

    \synopsis
    \begin{verbatim}
    int dict_isempty(dict_t *);\end{verbatim}

    \description
    The \verb|dict_isempty| function returns 1 if the given dictionary is
    empty, otherwise it returns 0.

\subsubsection{The {\tt dict_isfull} function}

    \indexfunc{dict_isfull}

    \synopsis
    \begin{verbatim}
    int dict_isfull(dict_t *);\end{verbatim}

    \description
    The \verb|dict_isfull| function returns 1 if the dictionary is full,
    otherwise it returns 0.

    If the argument is an expression with side effects, the behavior is
    undefined.\index{macros!and side effects}

\subsubsection{The {\tt dict_contains} function}

    \indexfunc{dict_contains}

    \synopsis
    \begin{verbatim}
    int dict_contains(dict_t *, dnode_t *);\end{verbatim}

    \description
    The \verb|dict_contains| function searches the given dictionary to
    determine whether the given node is an occupant. If the node is found, 1 is
    returned, otherwise 0 is returned.\footnote{The intent is to support
    verification.  The search may be inefficient compared to {\tt
    dict_lookup}.}

\subsubsection{The {\tt dict_allow_dupes} function}

    \label{section:dict_allow_dupes}
    \indexfunc{dict_allow_dupes}

    \synopsis
    \begin{verbatim}
    void dict_allow_dupes(dict_t *);\end{verbatim}

    \constraints
    The dictionary specified by the first argument shall be empty.

    \description
    The \verb|dict_allow_dupes| function configures the given dictionary to
    support duplicate keys. This can only be done when the dictionary is empty,
    and the change cannot be reverted.

\subsubsection{The {\tt dnode_is_in_a_dict} function}

    \indexfunc{dnode_is_in_a_dict}

    \synopsis
    \begin{verbatim}
    int dnode_is_in_a_dict(dnode_t *);\end{verbatim}

    \description
    The \verb|dnode_is_in_a_dict| function reports whether the given node
    is currently the occupant of some dictionary. If so, 1 is returned.
    Otherwise 0 is returned.

\subsubsection{The {\tt dnode_create} function}

    \indexfunc{dnode_create}

    \synopsis
    \begin{verbatim}
    dnode_t *dnode_create(void *);\end{verbatim}

    \description
    The \verb|dnode_create| function dynamically allocates a dictionary node,
    stores in it the data value specified in the argument and
    returns a pointer to it. The allocation is performed by a call to the
    standard \verb|malloc| function. If the allocation fails, a null
    pointer is returned.

    The node's key pointer remains indeterminate until it is the subject of a
    \verb|dict_insert| operation.

\subsubsection{The {\tt dnode_init} function}

    \indexfunc{dnode_init}

    \synopsis
    \begin{verbatim}
    dnode_t *dnode_init(dnode_t *, void *);\end{verbatim}

    \description
    The \verb|dnode_init| function initializes the contents
    of the specified dictionary node object, assigning it the
    data value specified as the second argument. 
    The first argument is a pointer which refers to 
    a data object that has a suitable size and alignment
    for the representation of an \verb|dnode_t| type.
    After initialization with \verb|dnode_init|, the object is subsequently
    eligible as an operand to the functions of the dictionary component,
    other than \verb|dnode_getkey|.

    The node's key pointer remains indeterminate until it is the subject of a
    \verb|dict_insert| operation.

\subsubsection{The {\tt dnode_destroy} function}

    \indexfunc{dnode_destroy}

    \synopsis
    \begin{verbatim}
    void dnode_destroy(dnode_t *);\end{verbatim}

    \description
    The \verb|dnode_destroy| function destroys a dictionary node that has been
    allocated with \verb|dnode_create|.  The value of any pointer
    that referred to the node that was thus freed is indeterminate.

    If the node is currently the occupant of a dictionary, the behavior is
    undefined if the hash is subsequently used.

\subsubsection{The {\tt dnode_get} function}

    \indexfunc{dnode_get}

    \synopsis
    \begin{verbatim}
    void *dnode_get(dnode_t *);\end{verbatim}

    \description
    The \verb|dnode_get| function retrieves the \verb|void * | data value
    associated with the given dictionary node.

\subsubsection{The {\tt dnode_getkey} function}

    \indexfunc{dnode_getkey}

    \synopsis
    \begin{verbatim}
    const void *dnode_getkey(dnode_t *);\end{verbatim}

    \description

    The \verb|dnode_getkey| function retrieves the \verb|void *| key value 
    associated with the given node. A node acquires an associated key
    when it is inserted into a dictionary (see section \ref{section:dict_insert}).
    Invoking \verb|dnode_getkey| on a node that has not been inserted
    into a dictionary results in undefined behavior.

\subsubsection{The {\tt dnode_put} function}

    \indexfunc{dnode_put}

    \synopsis
    \begin{verbatim}
    void dnode_put(dnode_t *, void *);\end{verbatim}

    \description
    The function \verb|dnode_put| replaces the data element
    associated with the dictionary node.

\subsubsection{The {\tt dict_process} function}

    \label{section:dict_process}
    \indexfunc{dict_process}

    \synopsis
    \begin{verbatim}
    void dict_process(dict_t *, void *, dnode_process_t);\end{verbatim}

    \description
    The \verb|dict_process| function iterates over the nodes of a dict,
    and for each node invokes a callback function.\footnote{In most cases,
    it is more convenient and preferable to 
    iterate over the dict using explicit calls to {\tt dict_first}
    and {\tt dict_next}.}
    The second argument is a {\it context pointer\/} which can have any value.
    The third argument of
    \verb|dict_process| shall be a pointer to a function which is compatible
    with the specified type. If the dict contains one or more nodes,
    then the function is invoked once for each node, in order from first
    to last. On each invocation, the first argument of the callback is a
    pointer to the dict; the second argument is a pointer to a node, called
    the {\it subject node}; and the third argument repeats the context pointer
    value that was originally passed to \verb|dict_process|.

    The callback function may delete the subject node by, for instance, calling
    \verb|dict_delete|. It may insert new nodes into the dictionary;
    however, if such an insertion causes the subject node to acquire
    a new successor, it is implementation-defined whether upon returning
    from the callback function, the traversal shall continue with the
    new successor, or with the original successor.
    
    The callback function, and any function invoked from the callback
    function, shall not destroy the dictionary or make any modifications
    other than the insertion of new nodes, or the deletion of the 
    subject node.

    The callback function may recursively invoke \verb|dict_process| for the
    same dictionary or for a different dictionary; the callback invocations arising out of
    the nested call inherit all of the restrictions of the outer callback in
    addition to being subject to the usual restrictions.\footnote{This means,
    for instance, that if two callbacks are in progress for different
    subject nodes from the same dictionary, the inner callback may not delete
    its subject node, because it inherits the restriction that the only
    permitted deletion is the outer callback's subject node.}

    The callback function may freely operate on a different dictionary,
    subject to any inherited restrictions.

\subsubsection{The {\tt dict_load_begin} function}

    \label{section:dict_load_begin}
    \indexfunc{dict_load_begin}

    \synopsis
    \begin{verbatim}
    void dict_load_begin(dict_load_t *, dict_t *);\end{verbatim}

    \constraints
    The dictionary specified by the second argument is empty.

    \description
    The \verb|dict_load_begin| function prepares a context object
    for the task of constructing the contents of a dictionary  out of
    a sequence of elements which is already sorted according to the
    sorting function of the dictionary.\footnote{This process is more efficient 
    than inserting all of the elements into a dictionary using {\tt dict_insert}. 
    In the reference implementation, this process runs in linear time, or $O(n)$
    whereas construction by repeated insertions runs in $O(n\log n)$ time.}
    The actual construction is performed
    by zero or more calls to \verb|dict_load_next| and is finalized by
    \verb|dict_load_end|.

    The \verb|dict_load_begin| function is said to bind the dictionary
    and context object together; the only way to unbind the two 
    is by calling \verb|dict_load_end| on the context object.

    The program shall not manipulate a dictionary that is bound to
    a context object, other than by calling \verb|dict_load_next|.

    The program shall not attempt to bind a dictionary to more than one context
    object simultaneously, or a context object to more than one dictionary
    simultaneously.

\subsubsection{The {\tt dict_load_next} function}

    \label{section:dict_load_next}
    \indexfunc{dict_load_next}

    \synopsis
    \begin{verbatim}
    void dict_load_next(dict_load_t *, dnode_t *, const void *);\end{verbatim}

    \constraints
    The node pointed at by the second argument is not an occupant of
    any dictionary. The key specified by the third argument is greater
    than or equal to all keys specified in previous calls to 
    \verb|dict_load_next| in the context of the same construction,
    according to the comparison function of the dictionary that is
    being constructed. That is to say, successive calls specify monotonically
    increasing keys.
    The dictionary is not full.

    \description
    The \verb|dict_load_next| function continues the construction of a
    dictionary from an ordered list of elements by specifying the next
    node in the sequence, along with its key. After this call, the node
    is considered to be inserted into the dictionary as if by
    \verb|dict_insert|.

\subsubsection{The {\tt dict_load_end} function}

    \label{section:dict_load_end}
    \indexfunc{dict_load_end}

    \synopsis
    \begin{verbatim}
    void dict_load_end(dict_load_t *);\end{verbatim}

    \description
    The \verb|dict_load_end| function finalizes the construction of
    a dictionary from a ordered sequence.  It breaks the binding between
    the \verb|dict_load_t| context object and the dictionary.

\subsection{Implementation}

TODO

\section{Exception component}
\label{section:exception_component}
\index{Exception}

The Exception component provides distributed error handling in the form of
exceptions, behind an interface designed to be implementable using only the
portable features of standard C. The features of this interface are:
\begin{itemize}
\item the ability to set up nested try-catch regions which declare specific
exceptions that they can handle;
\item grouped exceptions, allowing handlers to catch specific exceptions,
or any exception within a group;
\item the ability to designate a function that is called in the event
that an exception is thrown that has no handler.
\item a mechanism for releasing resources acquired by code that is terminated
by an exception;
\item the ability to pass dynamically allocated data from the throw site to the
catch site.
\end{itemize}

An exception is simply a means of returning to a prior place in the program's
execution. The ANSI C language provides crude, but portable, exception handling
consisting of the \verb|jmp_buf| type, the \verb|setjmp| macro and the
\verb|longjmp| function. The Kazlib Exception component can be implemented in
terms of these primitives. The constraint to implementability in standard C
leads to a number of concessions:
\begin{itemize}
\item A program can leave cleanup regions and try-catch regions by improper
means, such as using \verb|goto|, \verb|return| or \verb|break|. This is
difficult to diagnose, and is simply documented as undefined behavior.
There is no support in the standard language for designating code that is
executed whenever a statement block terminates by any means.
\item For the same reason, the exception handling interface described here
has an explicit mechanism for deallocation of resources associated with
statement blocks that are terminated by exceptions. This interface is
not as convenient as language support for automatic cleanup. Correct
management of temporary dynamic resources using this interface requires
programmer discipline.
\item The requirement to be able to use \verb|setjmp| to save a context
to be later returned to during exception processing brings in restrictions
related to non-volatile objects. If non-volatile objects are modified 
between the time an exception handling region is initiated and the time
an exception is caught in the region, these objects have indeterminate
values.\footnote{This liberty in ANSI C allows compiler
or library writers to implement {\tt setjmp} as a simple mechanism that
takes a snapshot of the machine context. Objects that are optimized into
special storage---such as registers---and whose values change since the
context saving operation will be clobbered when the context is restored
by {\tt longjmp}.} 
\end{itemize}

\subsection{Interface}

\subsubsection{The {\tt except.h} header}

Each C or C++ translation unit that is to use the functionality of the Exception
component shall include the header \verb|except.h|. This header shall
contain declarations of types and external functions, and definitions of
macros.  The following typedef names shall be
defined:\index{Exception!typedef names}
\begin{verbatim}
    except_id_t
    except_t
\end{verbatim}
The following external function names shall be declared:
\index{Exception!function names}\index{functions!defined by Exception}
\begin{verbatim}
    except_init                 except_group   
    except_deinit               except_message 
    except_rethrow              except_data    
    except_throw                except_take_data
    except_throwd               except_set_allocator
    except_throwf               except_alloc
    except_unhandled_catcher    except_free
    except_code            
\end{verbatim}
The following preprocessor symbols shall be
defined: \index{Exception!macro names}\index{macros!defined by Exception}
\indexmacro{XCEPT_H}
\begin{verbatim}
    XCEPT_H                     except_cleanup_pop
    XCEPT_GROUP_ANY             except_checked_cleanup_pop
    XCEPT_CODE_ANY              except_try_push
    XCEPT_BAD_ALLOC             except_try_pop
    except_cleanup_push
\end{verbatim}
Finally, these two enum constants are defined:
\begin{verbatim}
    except_no_call
    except_call
\end{verbatim}
\index{symbols!reserved by Exception}\index{Exception!reserved symbols} Macro
identifiers which begin with the upper-case prefix \verb|XCEPT|\footnote{The
prefix {\tt XCEPT} is used rather than {\tt EXCEPT} because ISO 9899 reserves
preprocessor symbols beginning with {\tt E} followed by a digit or
capital letter for future extensions to the {\tt <errno.h>} header.}
are reserved for future extensions to the \verb|except.h|
header, as are names in the ordinary and tag namespaces which begin with
\verb|except_|. External names which begin with \verb|except_| are reserved by
the Kazlib library regardless of what headers are included.

\subsubsection{The {\tt except_id_t} type}

\label{section:except_id_t}
\indextype{except_id_t}
\indexmacro{XCEPT_GROUP_ANY}
\indexmacro{XCEPT_CODE_ANY}
The type \verb|except_id_t| is an aggregate consisting of two unsigned long
values which represent an {\it exception group\/} and {\it exception code},
respectively, in that order.\footnote{Thus, the program may initialize
an {\tt except_id_t} object using two brace-enclosed initializers which
specify the group and code.} An exception group is a value which identifies a
group of related exceptions. An exception code is a value which identifies a
specific exception uniquely within a group.  The codes are assigned by the
program designer. The Exception component reserves only the group and code
values of zero, which, when used to specify a catch, match any value.

The preprocessor symbols \verb|XCEPT_GROUP_ANY| and
\verb|XCEPT_CODE_ANY| each expand to a constant integral expression having the
value zero.  These symbols are intended, in a catch specification, to clearly
convey that any exception or any group is being caught.

The preprocessor symbol \verb|XCEPT_BAD_ALLOC| expands to an integral constant
expression having the value 1. This symbol is intended to represent the
standard exception group for failed memory allocations.
(See section \ref{section:except_throwf}).

The exception groups from 1 to 15 are reserved for implementation use.

\subsubsection{The {\tt except_t} type}

\indextype{except_t}
An object of type \verb|except_t| keeps track of all of the information that is
passed when an exception is thrown, and is known as an {\it exception
descriptor}.  The type is opaque, hence the program shall manipulate this type
using only the interface functions provided.

\subsubsection{The {\tt except_init} function}

    \indexfunc{except_init}

    \synopsis
    \begin{verbatim}
    int except_init(void);\end{verbatim}

    \description
    The \verb|except_init| function allocates resources needed by the
    Exception component.  Before using any of the other exception interface
    functions or macros, the program shall perform at least one successful call
    to \verb|except_init|.

    If the initialization succeeds, \verb|except_init| returns 1. Otherwise
    it returns 0.

    The \verb|except_init| function may be called more than once. After a
    successful call, every subsequent call shall be successful up to an
    implementation-defined maximum number of repetitions, which shall be at least
    as large as the \verb|INT_MAX| from \verb|limits.h|. \footnote{
    The intent is to support, but not enforce, a style of global initialization
    whereby each module which requires the use of another module calls its
    initialization function from its own initialization function. Only the
    first such call performs the initialization of the module; subsequent calls
    merely increment a counter. During deinitialization, the counter is
    decremented and cleanup takes place when the counter reaches zero.}

\subsubsection{The {\tt except_deinit} function}

    \indexfunc{except_deinit}

    \synopsis
    \begin{verbatim}
    void except_deinit(void);\end{verbatim}

    \description
    The \verb|except_deinit| function releases the resources 
    that were allocated by \verb|except_init|.

    For the resource deallocation to actually take place, the
    \verb|except_deinit| must be called as many times as the
    number of times \verb|except_init| was successfully called.

    If \verb|except_deinit| is called more times than \verb|except_init| is
    successfully called, the behavior is undefined.

\subsubsection{The {\tt except_rethrow} function}

    \indexfunc{except_rethrow}

    \synopsis
    \begin{verbatim}
    void except_rethrow(except_t *);\end{verbatim}
    
    \description
    The rethrow function is used to rethrow a caught exception.  The argument
    shall not be null. An exception shall not be rethrown from outside of the
    {\it try-catch region\/} in which it was caught. An exception shall not be
    rethrown from a try-catch region other than the one in which it was caught.
    It shall not be rethrown from a try-catch or cleanup region enclosed within
    the one in which it was caught.

    When an exception is rethrown, the search for a handler does not begin with
    the region in which the exception was caught. Instead, this region is
    terminated, and the search continues with the enclosing one, if one
    exists.

\subsubsection{The {\tt except_throw} function}

    \indexfunc{except_throw}

    \synopsis
    \begin{verbatim}
    void except_throw(long, long, const char *);\end{verbatim}

    \constraints
    The first two arguments specify the exception group and code,
    respectively. Neither of these arguments shall be zero.

    \description
    The \verb|except_throw| function causes an exception to be thrown.

    If the throw takes place in a try-catch region where an exception
    was just caught, this original exception is considered handled. In
    this case, the new exception is still eligible for handling by the
    same try-catch region.

    The third argument points to the first character of a string
    which becomes the {\it exception message}. Because the throwing of
    the exception may cause the current statement block to terminate,
    this string data shall be non-local. It may be a string literal, since the
    implementation shall not modify the message, or it may be an ordinary
    object of static duration. If it is dynamic data, it becomes the handler's
    responsibility to extract the message from the caught exception and
    free the data.\footnote{The programmer should consider using 
    {\tt except_throwd} to pass arbitrary dynamic data from the throw
    site to the try-catch region.}

    The \verb|except_throw| function does not return. The implementation
    searches for a suitable try-catch region starting with the one
    initiated by the most recent \verb|except_try_push|. If there
    is no enclosing region, the search fails.  Otherwise if a match is found,
    execution continues at the start of the target try-catch region, appearing
    to be a second return from \verb|except_try_push| distinguished by a non-null
    value of the \verb|except_t *| object.

    If no match is found during exception processing, the exception is
    handled internally by the implementation. The implementation then
    calls the currently registered function for catching unhandled
    exceptions (see section \ref{section:except_unhandled_catcher}).

    The default catcher for unhandled exceptions shall terminate the program
    with a diagnostic which identifies the code, group and exception message.

    During the search for an exception handler, cleanup handlers may be
    encountered. They are removed from the inside out and called with
    their registered arguments. This process is called {\it unwinding}.
    \index{unwinding}

\subsubsection{The {\tt except_throwd} function}

    \indexfunc{except_throwd}

    \synopsis
    \begin{verbatim}
    void except_throwd(long, long, const char *, void *);\end{verbatim}

    \constraints
    The first two arguments specify the exception group and code,
    respectively. Neither of these arguments shall be zero.

    \description
    The \verb|except_throwd| function is the same as \verb|except_throw| in
    every respect except that it has an additional \verb|void *| parameter. A
    null argument may be used for this parameter, or it may be any valid
    pointer value.

    When the exception is handled, and the handler does not remove this pointer
    using \verb|except_take_data| then the implementation shall automatically
    invoke the function \verb|except_free| on this pointer.

\subsubsection{The {\tt except_throwf} function}

    \indexfunc{except_throwf}
    \label{section:except_throwf}

    \synopsis
    \begin{verbatim}
    void except_throwf(long, long, const char *, ...);\end{verbatim}

    \constraints
    The first two arguments specify the exception group and code,
    respectively. Neither of these arguments shall be zero.

    \description

    This function is almost exactly the same as \verb|except_throw|
    except that the exception message is not directly specified.
    Instead, the \verb|char *| argument specifies a format string which may be
    followed by trailing arguments. The format string and trailing arguments
    are interpreted as the format string and arguments of the standard C
    function \verb|printf| and are subject to the same requirements.
    
    The format string is interpreted, and the results of formatting are placed into
    buffer provided by the implementation.  The implementation shall provide
    space for at least 1024 bytes of storage for the result of the formatting,
    including the null terminator byte. If the formatting requires more space
    than the implementation provides, the behavior is undefined.

    The results of the formatted print shall become the exception message
    of the thrown exception.

    If the implementation is unable to allocate resources for the formatted
    message, it shall throw a code 1 exception having an unspecified code in
    group \verb|XCEPT_BAD_ALLOC| with an implementation-defined message.
    (See section \ref{section:except_id_t}).

\subsubsection{The {\tt except_unhandled_catcher} function}

    \label{section:except_unhandled_catcher}
    \indexfunc{except_unhandled_catcher}

    \synopsis
    \begin{verbatim}
    void (*except_unhandled_catcher(void (*)(except_t *)))
            (except_t *);\end{verbatim}

    \description
    The \verb|except_unhandled_catcher| function installs a new
    function for catching unhandled exceptions. The argument is a 
    pointer to a catching function that returns nothing, and accepts a pointer
    of type \verb|except_t *|.  A pointer to the previously installed
    catching function is returned. If the program did not previously
    install a catching function, then a pointer to the default catching
    function is returned. The program may retain this pointer and
    use it to reinstall the default function.

    A function for catching unhandled exceptions should not return. If it
    returns, the implementation shall terminate the program with a diagnostic.

\subsubsection{The {\tt except_code} function}

    \indexfunc{except_code}

    \synopsis
    \begin{verbatim}
    unsigned long except_code(except_t *);\end{verbatim}

    \description
    The \verb|except_code| is an accessor function which returns the
    exception code of the given exception descriptor.

\subsubsection{The {\tt except_group} function}

    \indexfunc{except_group}

    \synopsis
    \begin{verbatim}
    unsigned long except_group(except_t *);\end{verbatim}

    \description
    The \verb|except_group| is an accessor function which returns the
    exception group of the given exception descriptor.

\subsubsection{The {\tt except_message} function}

    \indexfunc{except_message}

    \synopsis
    \begin{verbatim}
    const char *except_message(except_t *);\end{verbatim}

    \description
    The \verb|except_group| is an accessor function which returns 
    a pointer to the string of text that was specified when the
    exception was thrown (the exception message).

\subsubsection{The {\tt except_data} function}

    \indexfunc{except_data}

    \synopsis
    \begin{verbatim}
    void *except_data(except_t *);\end{verbatim}

    \description
    The \verb|except_group| returns the data pointer that
    was specified in the \verb|except_throwd| call.
    If the exception was not thrown by \verb|except_throwd|
    the return value is unspecified.


\subsubsection{The {\tt except_take_data} function}

    \indexfunc{except_take_data}

    \synopsis
    \begin{verbatim}
    void *except_take_data(except_t *);\end{verbatim}

    \description
    The \verb|except_take_data| returns the data pointer that
    was specified in the \verb|except_throwd| call, and
    updates the exception descriptor so that the pointer is
    set to null.

    If the exception was not thrown by \verb|except_throwd|
    the result is unspecified.

\subsubsection{The {\tt except_cleanup_push} macro}

    \indexmacro{except_cleanup_push}

    \synopsis
    \begin{verbatim}
    void except_cleanup_push(void (*)(void *), void *);\end{verbatim}

    \description
    The call to \verb|except_cleanup_push| shall be matched with a call to
    \verb|except_cleanup_pop| which must occur in the same statement block at
    the same level of nesting.\footnote{This requirement allows an implementation
    to provide an {\tt except_cleanup_push} macro which opens up a statement
    block and a {\tt except_cleanup_pop} which closes the statement block.
    The space for the registered pointers can then be efficiently allocated
    from automatic storage.}

    The \verb|except_cleanup_push| macro registers a cleanup handler that will
    be called if an exception subsequently occurs before the matching
    \verb|except_cleanup_pop| is executed, and is not intercepted and handled by
    a try-catch region that is nested between the two.

    The first argument to \verb|except_cleanup_push| is a pointer
    to the cleanup handler, a function that returns nothing and takes
    a single argument of type \verb|void *|. The second argument
    is a \verb|void *| value that is registered along with the handler.
    This value is what is passed to the registered handler, should it
    be called.

    Cleanup handlers are called in the reverse order of their nesting: inner
    handlers are called before outer handlers.

    The program shall not leave the cleanup region between the call to the macro
    \verb|except_cleanup_push| and the matching call to
    \verb|except_cleanup_pop| by means other than throwing an exception, or
    calling \verb|except_cleanup_pop|.

    Within the call to the cleanup handler, it is possible that new exceptions
    may happen.  Such exceptions must be handled before the cleanup handler
    terminates. If the call to the cleanup handler is terminated by an
    exception, the behavior is undefined.\footnote{The exception which triggered
    the cleanup is not yet caught; thus the program would be effectively trying
    to replace an exception with one that isn't in a well-defined state.}

\subsubsection{The {\tt except_cleanup_pop} macro}

    \indexmacro{except_cleanup_pop}
    \label{section:except_cleanup_pop}

    \synopsis
    \begin{verbatim}
    void except_cleanup_pop(int);\end{verbatim}

    \description
    A call to the \verb|except_cleanup_pop| macro shall match each
    call to \verb|except_cleanup_push| which shall be in the
    same statement block at the same nesting level.  It shall
    match the most recent such a call that is not matched
    by a previous \verb|except_cleanup_pop| at the same level.

    This macro causes the registered cleanup handler to be removed.  If, and
    only if the argument is other than zero, the cleanup handler is called.
    In that case, the registered context pointer is passed to the cleanup
    handler.

    \indexenum{except_no_call}
    \indexenum{except_call}
    The enumeration constants \verb|except_no_call| and \verb|except_call|
    may be used as arguments to this function instead of
    the equivalent constants \verb|0| and \verb|1|.

    The program shall not leave the region between the call to the macro
    \verb|except_cleanup_push| and the matching call to
    \verb|except_cleanup_pop| other than by throwing an exception, or
    by executing the \verb|except_cleanup_pop|.

\subsubsection{The {\tt except_checked_cleanup_pop} macro}

    \indexmacro{except_checked_cleanup_pop}

    \synopsis
    \begin{verbatim}
    void except_checked_cleanup_pop(void (*)(void *), int);\end{verbatim}

    \constraints
    The first pointer-to-function argument shall match the pointer value that
    was registered by the matching \verb|except_cleanup_push| macro.

    \description
    The \verb|except_checked_cleanup_pop| macro may be used as an alternative to
    \verb|except_cleanup_pop|. In verification mode, the constraint serves to
    provide additional safety by making an explicit declaration regarding which
    handler is being called (or ignored, as the case may be).

    The program shall not leave the region between the call to the macro
    \verb|except_cleanup_push| and the call to
    \verb|except_checked_cleanup_pop| by means other than throwing an
    exception, or executing the latter macro.

\subsubsection{The {\tt except_try_push} macro}

    \indexmacro{except_try_push}
    \label{section:except_try_push}

    \synopsis
    \begin{verbatim}
    void except_try_push(const except_id_t [],
            size_t, except_t **);\end{verbatim}

    \description
    The \verb|except_try_push| marks the beginning of a try-catch region
    of the program. It must be matched by a \verb|except_try_pop| written in
    the same statement block at the same level of nesting, which
    terminates the try-catch region. Regions may be nested.

    The program shall not leave a try-catch region other than by throwing
    an exception or by executing the \verb|except_try_pop|.\footnote{Thus,
    leaving the try-catch region using {\tt goto}, {\tt return},
    {\tt break} or {\tt continue} leads to undefined behavior.}

    The first argument is a pointer to the first element of an array of
    \verb|except_id_t| objects, the number of elements of which is specified by
    the second argument. The array specifies which exceptions are caught.
    The implementation shall treat this array as read-only.\footnote{Thus,
    the program may allocate the array in static storage.}

    The third argument of \verb|except_try_push| shall point to an object
    of type \verb|except_t *|. After the call to \verb|except_try_push|,
    the program shall inspect the value of this object. A null value indicates
    that no exception has been thrown. A non-null value indicates that an
    exception was thrown, and is now caught. In other words, when an exception
    is caught by a try-catch region, then control passes from the throw site
    back to the first statement after the \verb|except_try_push| statement of
    the try-catch region. This case is distinguished from an ordinary return by
    the non-null value of the pointer object that was specified by the third
    argument of the earlier call to \verb|except_try_push|.

    An exception is considered handled if it is caught in a try-catch region
    which subsequently terminates by executing its \verb|except_try_pop| or by
    throwing another exception.  When an exception is considered handled, any
    dynamic data that was associated with that exception is
    freed.\footnote{Dynamic data may be explicitly associated with an exception
    using {\tt except_throwd}. Other types of throw may associate unspecified
    dynamic data.} It's possible for more than one exception to be active
    at once. During the processing of one exception, a try-catch region
    which catches the exception may execute a nested try-catch region
    in which independent exception processing takes place. Provided that 
    no exception escapes from the inner try-catch region, the original
    exception remains pending. But if an exception escapes from the inner
    region, it causes the original exception to be handled.\footnote{Thus, a
    given try-catch region cannot catch multiple exceptions concurrently.}
   
    The caught exception may be rethrown by calling \verb|except_rethrow|,
    specifying the the value of the caught exception descriptor as the
    argument.  Rethrowing a caught exception causes the innermost try-catch
    region to terminate, but the exception is not considered handled. The
    search for a handler continues with the second most enclosing region.

    Throwing a new exception during the handling of a caught exception may
    cause the {\it same\/} try-catch region to catch that exception; the
    try-catch region is not terminated until it is determined that it doesn't
    catch the new exception.

    Each entry in the array of \verb|except_id_t| objects specifies what
    exceptions are caught by the try-catch region. When an exception is
    thrown, the implementation searches for the inner-most try-catch region
    which has at least one match for the thrown exception in its catch
    specification array. 

    A match occurs when a specification exactly matches the group and code of
    the thrown exception. If a catch specification is for group 0, then it
    matches any group. If a catch specification is for code 0, then it matches
    any exception code. A catch specification of group 0 and code 0 catches all
    exceptions.

    Non-volatile automatic variables that are local to the function containing
    the try-catch region, and that are modified after \verb|except_try_push|
    begins the try-catch region have indeterminate values when an exception is
    caught.

    Once a caught exception is handled or re-thrown, the value of the
    \verb|except_t *| pointer which referenced it becomes indeterminate.
    If a re-thrown exception is caught again, the implementation shall
    produce a valid \verb|except_t *| pointer.

    \example
    The following example illustrates the use of \verb|except_try_push| and
    related macros and functions.
    \begin{verbatim}
    #include <stdlib.h>
    #include <assert.h>
    #include "except.h"

    #define MY_GROUP 42
    #define MY_CODE   1

    static void func_that_throws(void)
    {
        except_throw(MY_GROUP, MY_CODE, "this is an exception");        
    }

    static void func_that_cleans_up(void)
    {
        void *local_data = malloc(10);

        except_cleanup_push(free, local_data);
        func_that_throws();
        except_checked_cleanup_pop(free, except_call);
    }

    void func_that_catches(void)
    {
        /* catch specification */
        static const except_id_t catch_spec[] = {
            { MY_GROUP, XCEPT_CODE_ANY }
        };
        /* exception handle */
        except_t *exc;

        except_try_push(catch_spec, 1, &exc);

        /*
         * Start of try-catch region: when exception is 
         * thrown, control returns here.
         */

        if (exc == 0) {
            /* try code that may throw an exception */

            func_that_cleans_up();
        } else {
            /* handle exception that was thrown */

            assert (except_group(exc) == MY_GROUP);
            printf("exception caught: %s %ld %ld\n",
                except_message(exc),
                except_group(exc), except_code(exc));

            goto terminate; /* ERROR! jumping out of try-catch */
        }

        /* end of try-catch region */

        except_try_pop();
    terminate:
        ;
    }
    \end{verbatim}
    In this example, the function \verb|func_that_catches| is intended to be
    called first.  It sets up a try-catch region which traps exceptions having
    the group identification \verb|MY_GROUP| (or 42). Any code within that
    group is caught because the code catch was specified as
    \verb|XCEPT_CODE_ANY|. When the \verb|except_try_push| macro is executed,
    it sets the value of \verb|exc| to null. Then \verb|func_that_cleans_up| is
    called, which throws an exception in the \verb|MY_GROUP| group. This
    exception is caught, so control resumes at the top of the try-catch region,
    with \verb|exc| set to a non-null value.  Thus the else clause of the if
    statement is now executed.  The handling code simply prints the exception
    message on standard output, as well as the numeric group and code.  The
    subsequent goto statement demonstrates a serious programming error.

    The \verb|func_that_cleans_up| function illustrates the use of cleanup
    regions. Dynamic memory is allocated which must not be allowed to leak
    when an exception is thrown, so a cleanup handler is set up to free the
    memory in that event. The standard C function \verb|free| happens to have,
    the right type signature and semantics that it can be used directly as a
    cleanup handler.   Should no exception be thrown, the cleanup pop macro
    will perform the call to the cleanup handler, because it is invoked with
    argument \verb|except_call|.

\subsubsection{The {\tt except_try_pop} macro}

    \indexmacro{except_try_pop}

    \synopsis
    \begin{verbatim}
    void except_try_pop(void);\end{verbatim}

    \description

    The \verb|except_try_pop| macro terminates a try-catch region. It must
    match a previous \verb|except_try_push| macro in the same statement
    block at the same level of nesting which is not already matched by an
    earlier \verb|except_try_pop|.

\subsubsection{The {\tt except_set_allocator} function}

    \indexfunc{except_set_allocator}
    \label{section:except_set_allocator}

    \synopsis
    \begin{verbatim}
    void except_set_allocator(void *(*)(size_t), void (*)(void *));\end{verbatim}

    \description
    The \verb|except_set_allocator| function installs a pair of allocator
    routines that will be used by the Exception component for future allocation
    and deallocation requests. 

    The first argument points to a function that resembles the standard C
    \verb|malloc| in type and semantics. The second argument points to a
    function that similarly resembles the standard C function \verb|free|.

    The default allocators are \verb|malloc| and \verb|free|. 
    The call
    \begin{verbatim}
    except_set_allocator(malloc, free);
    \end{verbatim}
    may be used to restore these default allocator functions.

    The program shall not call \verb|except_set_allocator| if an exception
    was thrown and has not yet been handled.\footnote{Doing so could, for example,
    create a mismatch whereby a pointer to data allocated with the previously installed
    allocator function would be passed to the new deallocator function.}

    The allocator function shall create a unique object consisting of at least
    as many bytes of storage as indicated by the value of the argument.
    The pointer returned shall be suitably aligned to represent an object
    of any type. If insufficient resources exist, the pointer returned shall be
    null. Requesting an object of zero size may produce a unique pointer
    that shall be acceptable to the deallocator function, or a null pointer.

    The deallocator function shall be capable of destroying objects created
    by the corresponding allocator function. Passing a null pointer to the
    deallocator shall have no effect.

\subsubsection{The {\tt except_alloc} function}

    \indexfunc{except_alloc}

    \synopsis
    \begin{verbatim}
    void *except_alloc(size_t);\end{verbatim}

    \description
    The \verb|except_alloc| function allocates memory using the default
    memory allocator or one installed by the program.
    (See section \ref{section:except_set_allocator}).

    If the allocation succeeds, a non-null pointer to the allocated object is
    returned.

    If the allocator indicates failure by returning a null pointer,
    then instead of returning, \verb|except_alloc| throws exception code 1 
    in the group \verb|XCEPT_BAD_ALLOC| (See section \ref{section:except_id_t}).

    If a zero size request is specified, then an exception is thrown or
    a non-null pointer is returned, depending on the treatment of such
    requests by the underlying allocator.

\subsubsection{The {\tt except_free} function}

    \indexfunc{except_free}

    \synopsis
    \begin{verbatim}
    void *except_free(void *);\end{verbatim}

    \description

    The \verb|except_free| function releases memory that was allocated
    using \verb|except_alloc|.  The deallocation is performed using the
    default allocator or one installed by the program.

    If an object is allocated by \verb|except_alloc|, then a 
    different allocator is installed, and the object is freed using
    \verb|except_free|, the behavior is undefined.

\subsection{Implementation}
\index{Exception component!reference implementation}

Described here is a reference implementation of the exception handling
interface that is covered in section \ref{section:exception_component}
The reference implementation requires only a conforming ANSI C implementation.
In particular, the actual mechanism for passing control from an exception throw
to a catch handler is based on the standard C \verb|setjmp| macro and
\verb|longjmp| function.

\subsubsection{Overview}

The core structure in the exception handling implementation is a stack that is
composed of a mixture of two types of nodes: cleanup nodes and catch nodes.
When an exception is thrown, the stack nodes are popped and processed starting
with the topmost one. 

The nodes are efficiently allocated in automatic storage by the macros
\verb|except_cleanup_push| and \verb|except_try_push|. These macros
open up a new statement block and declare the node information in automatic
storage.  These objects are then pushed onto the stack. The corresponding macros
\verb|except_cleanup_pop| and \verb|except_try_pop| pop the node off the stack
and close the statement block.

An static variable keeps track of the stack top. In the multi-threaded variant
of the code which is based on the POSIX threading interface, there is a
thread-specific stack top created using the thread-specific function
pthread_key_create. Using global variables is a compromise that simplifies the
interface; the throw functions simply ``know'' where the thread's exception
stack is, so the context information doesn't have to be passed around.

\subsubsection{Stack nodes}

A node in the exception handling stack contains a pointer to the next
node below, followed by a type field and a union which together keep
track of the appropriate type-specific data:
\begin{verbatim}
    enum except_stacktype {
        XCEPT_CLEANUP, XCEPT_CATCHER
    };

    struct except_stacknode {
        struct except_stacknode *except_down;
        enum except_stacktype except_type;
        union {
            struct except_catch *except_catcher;       
            struct except_cleanup *except_cleanup;
        } except_info;
    };
\end{verbatim}
The union overlaps pointers to structures instead of structures in order to
save space: there is a disparity in size between a cleanup node and a catch
node, so making them both use the same amount of space would be wasteful.
The space saving comes at a price, because the pointers themselves take up
extra space and time is spent initializing them. Some casting trickery
could be used to create a stack having two different kinds of structures
without the use of unions.

\paragraph{Cleanup nodes}

Cleanup nodes act as placeholders for a pointer to a cleanup handler function
and a context pointer to be passed to that function. The type-dependent
component of the cleanup node is declared like this:
\begin{verbatim}
    struct except_cleanup {
        void (*except_func)(void *);
        void *except_context;
    };
\end{verbatim}
The cleanup handler is invoked when the node is popped during exception
processing. A cleanup handler may also be invoked when the cleanup node is
removed by executing \verb|except_cleanup_pop| or
\verb|except_checked_cleanup_pop|. Whether or not this happens depends on the
integer parameter that is documented in section
\ref{section:except_cleanup_pop}.

\paragraph{Catch nodes}

The catch node structure is more complicated than the cleanup node.
Its definition depends on two additional types, \verb|except_id_t|
and \verb|except_t|, both of which also make play a role in the exception
component's interface.
\begin{verbatim}
    typedef struct {
        unsigned long except_group;
        unsigned long except_code;
    } except_id_t;

    typedef struct {
        except_id_t except_id;
        const char *except_message;
        void *except_dyndata;
    } except_t;

    struct except_catch {
        const except_id_t *except_id;
        size_t except_size;
        except_t except_obj;
        jmp_buf except_jmp;
    };
\end{verbatim}
The \verb|except_id| member of the \verb|except_catch| structure is a pointer to the
array of \verb|except_id_t| objects which specify what exceptions the node
catches. The \verb|except_size| member specifies the number of elements in the array.
Both of these values are derived directly from the arguments of the
\verb|except_try_push| macro (see section \ref{section:except_try_push}). The
\verb|except_obj| member provides storage for the caught exception. This member is
the means by which the thrown exception is communicated to the try-catch region
where it is caught. It contains the group and code identifiers, the exception
message and, optionally, the pointer to arbitrary exception data.  The
\verb|except_jmp| member is the standard C \verb|jmp_buf|---a place for saving the
execution context so that it's possible to pass control, via \verb|longjmp|
from the place where an exception is thrown to the place where it is caught.

If, during the search for an exception handler, a catch node is encountered
which matches the thrown exception, the node remains the stack.  The exception
information is stored into into the node's \verb|except_obj| member and a
\verb|longjmp| is executed to return to the try-catch region in which the node
was allocated and pushed. Because the node is still on the stack, it's possible
to throw another exception which is caught again by the same node.  When an
exception is thus caught, control resumes just after the \verb|except_throw|
which placed the node onto the stack. The pointer passed into \verb|except_throw|
is updated  to point to the \verb|except_obj| member of the catch structure.
The program can then use the portable accessor functions such as
\verb|except_code| to gain information about the caught exception and handle it
accordingly.

\index{external names|see {functions}}
\index{reference implementation|see {implementation}}
\index{names|see {symbols}}
\index{identifiers|see {symbols}}
\index{structure names|see{tags}}
\index{preprocessor symbols|see{macros}}
\index{defines|see{macros}}
\index{reserved symbols|see{symbols}}
\index{symbols!preprocessor|see{macros}}
\index{symbols!type names|see{typedefs}}
\index{symbols!function names|see{functions}}
\printindex 

\end{document}
