string/FreeBSD/timingsafe_bcmp.c

   1 /*      $OpenBSD: timingsafe_bcmp.c,v 1.3 2015/08/31 02:53:57 guenther Exp $    */
   2 /*
   3  * Copyright (c) 2010 Damien Miller.  All rights reserved.
   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("$FreeBSD$");
  20
  21 #include <string.h>
  22
  23 int
  24 timingsafe_bcmp(const void *b1, const void *b2, size_t n)
  25 {
  26         const unsigned char *p1 = b1, *p2 = b2;
  27         unsigned char ret = 0;
  28
  29         for (; n > 0; n--) {
  30                 ret |= *p1++ ^ *p2++;
  31         }
  32
  33         /* map zero to zero and nonzero to one */
  34         return (ret + 0xff) >> 8;
  35 }