47 lines
1.6 KiB
C
47 lines
1.6 KiB
C
|
/* $OpenBSD: timingsafe_memcmp.c,v 1.2 2015/08/31 02:53:57 guenther Exp $ */
|
||
|
|
/*
|
||
|
|
* Copyright (c) 2014 Google Inc.
|
||
|
|
*
|
||
|
|
* 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.
|
||
|
|
*
|
||
|
|
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
|
||
|
|
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
|
||
|
|
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR 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.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#include <limits.h>
|
||
|
|
#include <string.h>
|
||
|
|
|
||
|
|
int
|
||
|
|
timingsafe_memcmp(const void *b1, const void *b2, size_t len)
|
||
|
|
{
|
||
|
|
const unsigned char *p1 = b1, *p2 = b2;
|
||
|
|
size_t i;
|
||
|
|
int res = 0, done = 0;
|
||
|
|
|
||
|
|
for (i = 0; i < len; i++) {
|
||
|
|
/* lt is -1 if p1[i] < p2[i]; else 0. */
|
||
|
|
int lt = (p1[i] - p2[i]) >> CHAR_BIT;
|
||
|
|
|
||
|
|
/* gt is -1 if p1[i] > p2[i]; else 0. */
|
||
|
|
int gt = (p2[i] - p1[i]) >> CHAR_BIT;
|
||
|
|
|
||
|
|
/* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */
|
||
|
|
int cmp = lt - gt;
|
||
|
|
|
||
|
|
/* set res = cmp if !done. */
|
||
|
|
res |= cmp & ~done;
|
||
|
|
|
||
|
|
/* set done if p1[i] != p2[i]. */
|
||
|
|
done |= lt | gt;
|
||
|
|
}
|
||
|
|
|
||
|
|
return (res);
|
||
|
|
}
|