From e2abcdca396661cbe0ae2ddb13d5c2b85682c13a Mon Sep 17 00:00:00 2001 From: Cem Keylan Date: Fri, 16 Oct 2020 17:41:25 +0300 Subject: initial commit --- lib/libc/string/timingsafe_memcmp.c | 47 +++++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) create mode 100644 lib/libc/string/timingsafe_memcmp.c (limited to 'lib/libc/string/timingsafe_memcmp.c') diff --git a/lib/libc/string/timingsafe_memcmp.c b/lib/libc/string/timingsafe_memcmp.c new file mode 100644 index 0000000..373f8cb --- /dev/null +++ b/lib/libc/string/timingsafe_memcmp.c @@ -0,0 +1,47 @@ +/* $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 +#include + +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); +} +DEF_WEAK(timingsafe_memcmp); -- cgit v1.2.3