1*854023f0SXin LI /* $OpenBSD: timingsafe_memcmp.c,v 1.2 2015/08/31 02:53:57 guenther Exp $ */
2*854023f0SXin LI /*
3*854023f0SXin LI * Copyright (c) 2014 Google Inc.
4*854023f0SXin LI *
5*854023f0SXin LI * Permission to use, copy, modify, and distribute this software for any
6*854023f0SXin LI * purpose with or without fee is hereby granted, provided that the above
7*854023f0SXin LI * copyright notice and this permission notice appear in all copies.
8*854023f0SXin LI *
9*854023f0SXin LI * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10*854023f0SXin LI * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11*854023f0SXin LI * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12*854023f0SXin LI * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13*854023f0SXin LI * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14*854023f0SXin LI * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15*854023f0SXin LI * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16*854023f0SXin LI */
17*854023f0SXin LI
18*854023f0SXin LI #include <limits.h>
19*854023f0SXin LI #include <string.h>
20*854023f0SXin LI
21*854023f0SXin LI int __timingsafe_memcmp(const void *, const void *, size_t);
22*854023f0SXin LI
23*854023f0SXin LI int
__timingsafe_memcmp(const void * b1,const void * b2,size_t len)24*854023f0SXin LI __timingsafe_memcmp(const void *b1, const void *b2, size_t len)
25*854023f0SXin LI {
26*854023f0SXin LI const unsigned char *p1 = b1, *p2 = b2;
27*854023f0SXin LI size_t i;
28*854023f0SXin LI int res = 0, done = 0;
29*854023f0SXin LI
30*854023f0SXin LI for (i = 0; i < len; i++) {
31*854023f0SXin LI /* lt is -1 if p1[i] < p2[i]; else 0. */
32*854023f0SXin LI int lt = (p1[i] - p2[i]) >> CHAR_BIT;
33*854023f0SXin LI
34*854023f0SXin LI /* gt is -1 if p1[i] > p2[i]; else 0. */
35*854023f0SXin LI int gt = (p2[i] - p1[i]) >> CHAR_BIT;
36*854023f0SXin LI
37*854023f0SXin LI /* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */
38*854023f0SXin LI int cmp = lt - gt;
39*854023f0SXin LI
40*854023f0SXin LI /* set res = cmp if !done. */
41*854023f0SXin LI res |= cmp & ~done;
42*854023f0SXin LI
43*854023f0SXin LI /* set done if p1[i] != p2[i]. */
44*854023f0SXin LI done |= lt | gt;
45*854023f0SXin LI }
46*854023f0SXin LI
47*854023f0SXin LI return (res);
48*854023f0SXin LI }
49*854023f0SXin LI
50*854023f0SXin LI __weak_reference(__timingsafe_memcmp, timingsafe_memcmp);
51