| 1 | /* extendbuf.c -- manage a dynamically-allocated buffer
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| 2 |
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| 3 | Copyright 2004 Free Software Foundation, Inc.
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| 4 |
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| 5 | This program is free software; you can redistribute it and/or modify
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| 6 | it under the terms of the GNU General Public License as published by
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| 7 | the Free Software Foundation; either version 2, or (at your option)
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| 8 | any later version.
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| 9 |
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| 10 | This program is distributed in the hope that it will be useful,
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| 11 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 13 | GNU General Public License for more details.
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| 14 |
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| 15 | You should have received a copy of the GNU General Public License
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| 16 | along with this program; if not, write to the Free Software Foundation,
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| 17 | Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
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| 18 |
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| 19 | /* Written by James Yougnman <jay@gnu.org>. */
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| 20 |
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| 21 | #if HAVE_CONFIG_H
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| 22 | # include <config.h>
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| 23 | #endif
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| 24 |
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| 25 | #include <stddef.h>
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| 26 | #include <stdlib.h>
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| 27 | #include <assert.h>
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| 28 | #include <errno.h>
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| 29 |
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| 30 | #include "xalloc.h"
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| 31 | #include "extendbuf.h"
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| 32 |
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| 33 |
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| 34 | /* We initially use a small default size to ensure that this code
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| 35 | * gets exercised.
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| 36 | */
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| 37 | #ifndef SIZE_DEFAULT
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| 38 | # define SIZE_DEFAULT 16
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| 39 | #endif
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| 40 |
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| 41 | static size_t
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| 42 | decide_size(size_t current, size_t wanted)
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| 43 | {
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| 44 | size_t newsize;
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| 45 |
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| 46 | if (0 == current)
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| 47 | newsize = SIZE_DEFAULT;
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| 48 | else
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| 49 | newsize = current;
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| 50 |
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| 51 | while (newsize < wanted)
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| 52 | {
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| 53 | if (2 * newsize < newsize)
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| 54 | xalloc_die ();
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| 55 | newsize *= 2;
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| 56 | }
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| 57 | return newsize;
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| 58 | }
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| 59 |
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| 60 |
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| 61 | void *
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| 62 | extendbuf(void* existing, size_t wanted, size_t *allocated)
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| 63 | {
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| 64 | int saved_errno;
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| 65 | size_t newsize;
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| 66 | void *result; /* leave uninitialised to allow static code checkers to identify bugs */
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| 67 |
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| 68 | saved_errno = errno;
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| 69 |
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| 70 | assert(wanted > 0u);
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| 71 | newsize = decide_size(*allocated, wanted);
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| 72 |
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| 73 | if ( (*allocated) == 0 )
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| 74 | {
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| 75 | /* Sanity check: If there is no existing allocation size, there
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| 76 | * must be no existing allocated buffer.
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| 77 | */
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| 78 | assert(NULL == existing);
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| 79 |
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| 80 | (*allocated) = newsize;
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| 81 | result = xmalloc(newsize);
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| 82 | }
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| 83 | else
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| 84 | {
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| 85 | if (newsize != (*allocated) )
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| 86 | {
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| 87 | (*allocated) = newsize;
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| 88 | result = xrealloc (existing, newsize);
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| 89 |
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| 90 | }
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| 91 | else
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| 92 | {
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| 93 | result = existing;
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| 94 | }
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| 95 | }
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| 96 |
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| 97 | if (result)
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| 98 | {
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| 99 | /* xmalloc() or xrealloc() may have changed errno, but in the
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| 100 | success case we want to preserve the previous value.
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| 101 | */
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| 102 | errno = saved_errno;
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| 103 | }
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| 104 | return result;
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| 105 | }
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