/*	$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);

}