path: root/contrib/bind/lib/isc/heap.mdoc

.\" $Id: heap.mdoc,v 8.4 1997/04/26 04:00:55 vixie Exp $
.\"
.\"Copyright (c) 1997 by Internet Software Consortium.
 *
.\"Permission to use, copy, modify, and distribute this software for any
.\"purpose with or without fee is hereby granted, provided that the above
.\"copyright notice and this permission notice appear in all copies.
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.\"THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
.\"ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
.\"OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
.\"CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
.\"DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
.\"PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
.\"ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
.\"SOFTWARE.
.\"
.Dd Jan 1, 1997
.\"Os OPERATING_SYSTEM [version/release]
.Os BSD 4
.\" TODO--get correct section # below!!
.Dt HEAP @SYSCALL_EXT@
.Sh DESCRIPTION
.Nm heap_new ,
.Nm heap_free ,
.Nm heap_insert ,
.Nm heap_delete ,
.Nm heap_increased ,
.Nm heap_decreased ,
.Nm heap_element ,
.Nm heap_for_each 
.Nd heap implementation of priority queues
.Sh SYNOPSIS
.Fd #include \&"heap.h\&"
.Ft heap_context    
.Fn heap_new "heap_higher_priority_func higher_priority" \
"heap_index_func index" "int array_size_increment"
.Ft int
.Fn heap_free "heap_context ctx"
.Ft int
.Fn heap_insert "heap_context ctx" "void *elt"
.Ft int
.Fn heap_delete "heap_context ctx" "int i"
.Ft int
.Fn heap_increased "heap_context ctx" "int i"
.Ft int
.Fn heap_decreased "heap_context ctx" "int i"
.Ft void *
.Fn heap_element "heap_context ctx" "int i"
.Ft int 
.Fn heap_for_each "heap_context ctx" "heap_for_each_func action" "void *uap"
.Sh DESCRIPTION
These functions implement heap\-based priority queues.  The user defines a
priority scheme, and provides a function for comparison of the priority
of heap elements
.Po see the description of the
.Ft heap_higher_priority_func
function pointer, below
.Pc .
.Pp
Each of the functions depends upon the
.Ft heap_context
type, which is a pointer to a
.Ft struct heap_context 
.Pq see Pa heap.h No for more information .
.Pp
The
.Pa heap.h
header file also defines the following set of function
function pointers:
.Bd -literal -offset indent
typedef int (*heap_higher_priority_func)(void *, void *);
typedef void (*heap_index_func)(void *, int);
typedef void (*heap_for_each_func)(void *, void *);
.Ed
.Pp
These are pointers to user-defined functions.
The 
.Ft heap_higher_priority_func
type is a pointer to a function which compares two
different heap (queue) elements and returns an
.Ft int
which answers the question, "Does the first queue element 
have a higher priority than the second?"  In other words, 
a function pointer of this type 
.Em must 
return a number greater than zero
if the element indicated by the first argument is of a higher priority than 
that indicated by the second element, and zero otherwise.  
.Pp
The other two function pointers are documented in the descriptions
of 
.Fn heap_new
.Pq Va heap_index_func
and
.Fn heap_for_each
.Pq Va heap_for_each_func ,
below.
.Pp
The function
.Fn heap_new
initializes a 
.Ft struct heap_context
and returns a pointer to it.  The
.Fa higher_priority
function pointer 
.Em must 
be 
.No non\- Ns Dv NULL .
As explained above, this refers to a 
function supplied by the user which compares the priority of two different
queue or heap elements; see above for more information. 
The second argument, 
.Fa index ,
is a pointer to a user-defined function whose arguments are
a heap element and its index in the heap.
.Fa Index 
is intended to provide the user a means of knowing the internal index
of an element in the heap while maintaining the opacity of the implementation;
since the user has to know the actual indexes of heap elements in order to use,
e.g., 
.Fn heap_delete
or
.Fn heap_element ,
the user 
.Fa index
function could store the index in the heap element, itself.  If 
.Fa index
is 
.No non\- Ns Dv NULL ,
then it is called 
.Em whenever 
the index of an element changes, allowing the user to stay up\-to\-date
with index changes.
The last argument, 
.Fa array_size_increment
will be used, as its name suggests, by
.Xr malloc 3
or
.Xr realloc 3
to increment the array which implements the heap; if zero, a default value 
will be used.
.Pp
The
.Fn heap_free
function frees the given
.Ft heap_context
argument 
.Pq Fa ctx ,
which also frees the entire
.Nm heap ,
if it is
.No non\- Ns Dv NULL .
The argument
.Fa ctx
should be
.No non\- Ns Dv NULL .
.Pp
The 
.Fn heap_insert
function is used to insert the new heap element
.Fa elt
into the appropriate place (priority\-wise) in the
.Ft heap
indicated by 
.Fa ctx
.Po a pointer to a
.Ft heap_context
.Pc .
If 
.No non\- Ns Dv NULL ,
the user-defined
.Ft higher_priority
function pointer associated with the indicated 
.Nm heap
is used to determine that
.Dq appropriate place ;
the highest\-priority elements are at the front of the queue (top of
the heap).
(See the description of 
.Fn heap_new , 
above, for more information.)
.Pp
The function
.Fn heap_delete
is used to delete the 
.Fa i\- Ns th
element of the queue (heap), and fixing up the queue (heap) from that
element onward via the priority as determined by the user function
pointed to by
.Ft higher_priority 
function pointer
.Pq see description of Fn heap_new, No above .
.Pp
.Fn heap_increased
.Pp
.Fn heap_decreased
.Pp
The 
.Fn heap_element
function returns the
.Fa i\- Ns th
element of the queue/heap indicated by
.Fa ctx ,
if possible.
.Pp
The
.Fn heap_for_each
function provides a mechanism for the user to increment through the entire
queue (heap) and perform some
.Fa action 
upon each of the queue elements.  This
.Fa action 
is pointer to a user\-defined function with two arguments, the first of
which should be interpreted by the user's function as a heap element.  The 
second value passed to the user function is just the
.Fa uap
argument to 
.Fn heap_for_each ;
this allows the user to specify additional arguments, if necessary, to
the function pointed to by 
.Fa action .
.\" The following requests should be uncommented and
.\" used where appropriate.  This next request is
.\" for sections 2 and 3 function return values only.
.Sh RETURN VALUES
.Bl -tag -width "heap_decreased()"
.It Fn heap_new
.Dv NULL
if unable to 
.Xr malloc 3
a 
.Ft struct heap_context
or if the
.Fa higher_priority
function pointer is 
.Dv NULL;
otherwise, a valid
.Ft heap_context 
.Ns .
.It Fn heap_free
-1 if 
.Fa ctx
is 
.Dv NULL 
(with 
.Va errno
set to
.Dv EINVAL ) ;
otherwise, 0.
.It Fn heap_insert
-1 
if either
.Fa ctx
or 
.Fa elt
is 
.Dv NULL ,
or if an attempt to 
.Xr malloc 3
or 
.Xr realloc 3
the heap array fails (with
.Va errno
set to 
.Dv EINVAL
or 
.Dv ENOMEM ,
respectively).
Otherwise, 0.
.It Fn heap_delete
-1 if 
.Fa ctx
is 
.Dv NULL
or 
.Fa i 
is out\-of\-range (with
.Va errno
set to
.Dv EINVAL ) ;
0 otherwise.
.It Fn heap_increased
As for
.Fn heap_delete .
.It Fn heap_decreased
As for
.Fn heap_delete .
.It Fn heap_element
NULL if 
.Fa ctx 
is 
.Dv NULL
or
.Fa i
out\-of-bounds (with
.Va errno
set to
.Dv EINVAL ) ;
otherwise, a pointer to the
.Fa i\- Ns th
queue element.
.It Fn heap_for_each
-1 if either
.Fa ctx
or 
.Fa action
is 
.Dv NULL
(with 
.Va errno
set to
.Dv EINVAL ) ;
0 otherwise.
.El
.\" This next request is for sections 1, 6, 7 & 8 only
.\" .Sh ENVIRONMENT
.Sh FILES
.Bl -tag -width "heap.h000"
.It Pa heap.h
 heap library header file
.El
.\" .Sh EXAMPLES
.\" This next request is for sections 1, 6, 7 & 8 only
.\"     (command return values (to shell) and
.\"    fprintf/stderr type diagnostics)
.Sh DIAGNOSTICS
Please refer to
.Sx RETURN VALUES .
.\" The next request is for sections 2 and 3 error
.\" and signal handling only.
.Sh ERRORS
The variable
.Va errno
is set by
.Fn heap_free , 
.Fn heap_insert , 
.Fn heap_delete , 
.Fn heap_increased , 
and
.Fn heap_decreased 
under the conditions of invalid input
.Pq Dv EINVAL
or lack of memory
.Pq Dv ENOMEM ;
please refer to
.Sx RETURN VALUES .
.Sh SEE ALSO
.Xr malloc 3 ,
.Xr realloc 3 .
.Pp
Cormen, Leiserson, and Rivest,  
.Sy Introduction to Algorithms,
MIT Press / McGraw Hill, 1990, ISBN 0\-262\-03141\-8, chapter 7.
.Pp
Sedgewick, 
.Sy Algorithms,
2nd ed'n, Addison\-Wesley, 1988, ISBN 0\-201\-06673\-4, chapter 11.
.\" .Sh STANDARDS
.\" .Sh HISTORY
.Sh AUTHORS
The
.Nm heap
library was implemented by Bob Halley (halley@vix.com) of Vixie Enterprises, 
Inc., for the Internet Software consortium, and was adapted from
the two books listed in the 
.Sx SEE ALSO
section, above.
.\" .Sh BUGS