1/*	$OpenBSD: timingsafe_memcmp.c,v 1.2 2015/08/31 02:53:57 guenther Exp $	*/
2/*
3 * Copyright (c) 2014 Google Inc.
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18#include <sys/cdefs.h>
19__FBSDID("$FreeBSD: stable/11/lib/libc/string/timingsafe_memcmp.c 319292 2017-05-31 06:47:56Z delphij $");
20
21#include <limits.h>
22#include <string.h>
23
24int __timingsafe_memcmp(const void *, const void *, size_t);
25
26int
27__timingsafe_memcmp(const void *b1, const void *b2, size_t len)
28{
29        const unsigned char *p1 = b1, *p2 = b2;
30        size_t i;
31        int res = 0, done = 0;
32
33        for (i = 0; i < len; i++) {
34                /* lt is -1 if p1[i] < p2[i]; else 0. */
35                int lt = (p1[i] - p2[i]) >> CHAR_BIT;
36
37                /* gt is -1 if p1[i] > p2[i]; else 0. */
38                int gt = (p2[i] - p1[i]) >> CHAR_BIT;
39
40                /* cmp is 1 if p1[i] > p2[i]; -1 if p1[i] < p2[i]; else 0. */
41                int cmp = lt - gt;
42
43                /* set res = cmp if !done. */
44                res |= cmp & ~done;
45
46                /* set done if p1[i] != p2[i]. */
47                done |= lt | gt;
48        }
49
50        return (res);
51}
52
53__weak_reference(__timingsafe_memcmp, timingsafe_memcmp);
54