1298691Sdelphij/*
2298691Sdelphij * Copyright (C) 2004-2007, 2011, 2012  Internet Systems Consortium, Inc. ("ISC")
3298691Sdelphij * Copyright (C) 1999-2001, 2003  Internet Software Consortium.
4298691Sdelphij *
5298691Sdelphij * Permission to use, copy, modify, and/or distribute this software for any
6298691Sdelphij * purpose with or without fee is hereby granted, provided that the above
7298691Sdelphij * copyright notice and this permission notice appear in all copies.
8298691Sdelphij *
9298691Sdelphij * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
10298691Sdelphij * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
11298691Sdelphij * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
12298691Sdelphij * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
13298691Sdelphij * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
14298691Sdelphij * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
15298691Sdelphij * PERFORMANCE OF THIS SOFTWARE.
16298691Sdelphij */
17298691Sdelphij
18298691Sdelphij/* $Id$ */
19298691Sdelphij
20298691Sdelphij/*! \file */
21298691Sdelphij
22298691Sdelphij#include <config.h>
23298691Sdelphij#include <limits.h>
24298691Sdelphij#include <isc/string.h>
25298691Sdelphij
26298691Sdelphij/* Making a portable memcmp that has no internal branches and loops always
27298691Sdelphij * once for every byte without early-out shortcut has a few challenges.
28298691Sdelphij *
29298691Sdelphij * Inspired by 'timingsafe_memcmp()' from the BSD system and
30298691Sdelphij * https://github.com/libressl-portable/openbsd/blob/master/src/lib/libc/string/timingsafe_memcmp.c
31298691Sdelphij *
32298691Sdelphij * Sadly, that one is not portable C: It makes assumptions on the representation
33298691Sdelphij * of negative integers and assumes sign-preserving right-shift of negative
34298691Sdelphij * signed values. This is a rewrite from scratch that should not suffer from
35298691Sdelphij * such issues.
36298691Sdelphij *
37298691Sdelphij * 2015-12-12, J. Perlinger (perlinger-at-ntp-dot-org)
38298691Sdelphij */
39298691Sdelphijint
40298691Sdelphijisc_tsmemcmp(const void *p1, const void *p2, size_t nb) {
41298691Sdelphij	const unsigned char *ucp1 = p1;
42298691Sdelphij	const unsigned char *ucp2 = p2;
43298691Sdelphij	unsigned int isLT = 0u;
44298691Sdelphij	unsigned int isGT = 0u;
45298691Sdelphij	volatile unsigned int mask = (1u << CHAR_BIT);
46298691Sdelphij
47298691Sdelphij	for (/*NOP*/; 0 != nb; --nb, ++ucp1, ++ucp2) {
48298691Sdelphij		isLT |= mask &
49298691Sdelphij		    ((unsigned int)*ucp1 - (unsigned int)*ucp2);
50298691Sdelphij		isGT |= mask &
51298691Sdelphij		    ((unsigned int)*ucp2 - (unsigned int)*ucp1);
52298691Sdelphij		mask &= ~(isLT | isGT);
53298691Sdelphij	}
54298691Sdelphij	return (int)(isGT >> CHAR_BIT) - (int)(isLT >> CHAR_BIT);
55298691Sdelphij}
56