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/* extendbuf.c -- manage a dynamically-allocated buffer
Copyright (C) 2004-2023 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
/* Written by James Yougnman <jay@gnu.org>. */
/* config.h must be included first. */
#include <config.h>
/* system headers. */
#include <assert.h>
#include <errno.h>
#include <stdlib.h>
/* gnulib headers. */
#include "xalloc.h"
/* find headers. */
#include "extendbuf.h"
/* We initially use a small default size to ensure that this code
* gets exercised.
*/
#ifndef SIZE_DEFAULT
# define SIZE_DEFAULT 16
#endif
static size_t
decide_size (size_t current, size_t wanted)
{
size_t newsize;
if (0 == current)
newsize = SIZE_DEFAULT;
else
newsize = current;
while (newsize < wanted)
{
if (2 * newsize < newsize)
return wanted;
newsize *= 2;
}
return newsize;
}
void *
extendbuf (void* existing, size_t wanted, size_t *allocated)
{
int saved_errno;
size_t newsize;
void *result; /* leave uninitialized to allow static code checkers to identify bugs */
saved_errno = errno;
assert (wanted > 0u);
newsize = decide_size (*allocated, wanted);
if ( (*allocated) == 0 )
{
/* Sanity check: If there is no existing allocation size, there
* must be no existing allocated buffer.
*/
assert (NULL == existing);
(*allocated) = newsize;
result = malloc (newsize);
}
else
{
if (newsize != (*allocated) )
{
(*allocated) = newsize;
result = realloc (existing, newsize);
if (NULL == result)
{
saved_errno = errno;
}
}
else
{
result = existing;
}
}
if (result)
{
/* malloc () or realloc () may have changed errno, but in the
success case we want to preserve the previous value.
*/
errno = saved_errno;
}
return result;
}
void *
xextendbuf (void* existing, size_t wanted, size_t *allocated)
{
void *p = extendbuf (existing, wanted, allocated);
if (NULL == p)
{
free (existing);
xalloc_die ();
}
return p;
}
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