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47 lines
1.6 KiB
C
47 lines
1.6 KiB
C
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/* $OpenBSD: timingsafe_memcmp.c,v 1.2 2015/08/31 02:53:57 guenther Exp $ */
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/*
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* Copyright (c) 2014 Google Inc.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include <limits.h>
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#include <string.h>
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int
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timingsafe_memcmp(const void *b1, const void *b2, size_t len)
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{
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const unsigned char *p1 = b1, *p2 = b2;
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size_t i;
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int res = 0, done = 0;
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for (i = 0; i < len; i++) {
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/* lt is -1 if p1[i] < p2[i]; else 0. */
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int lt = (p1[i] - p2[i]) >> CHAR_BIT;
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/* gt is -1 if p1[i] > p2[i]; else 0. */
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int gt = (p2[i] - p1[i]) >> CHAR_BIT;
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/* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */
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int cmp = lt - gt;
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/* set res = cmp if !done. */
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res |= cmp & ~done;
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/* set done if p1[i] != p2[i]. */
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done |= lt | gt;
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}
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return (res);
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}
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