mirror of
https://github.com/jart/cosmopolitan.git
synced 2025-01-31 11:37:35 +00:00
394d998315
At least in neovim, `│vi:` is not recognized as a modeline because it has no preceding whitespace. After fixing this, opening a file yields an error because `net` is not an option. (`noet`, however, is.)
96 lines
5.3 KiB
C
96 lines
5.3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
|
||
│ vi: set noet ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
|
||
╞══════════════════════════════════════════════════════════════════════════════╡
|
||
│ Copyright 2014 Google Inc. │
|
||
│ │
|
||
│ Permission to use, copy, modify, and/or 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 "libc/limits.h"
|
||
#include "libc/str/str.h"
|
||
|
||
asm(".ident\t\"\\n\\n\
|
||
timingsafe_memcmp (ISC License)\\n\
|
||
Copyright 2014 Google Inc.\"");
|
||
asm(".include \"libc/disclaimer.inc\"");
|
||
|
||
/**
|
||
* Lexicographically compares the first 𝑛 bytes in 𝑝 and 𝑞.
|
||
*
|
||
* The following expression:
|
||
*
|
||
* timingsafe_memcmp(p, q, n)
|
||
*
|
||
* Is functionally equivalent to:
|
||
*
|
||
* MAX(-1, MIN(1, memcmp(p, q, n)))
|
||
*
|
||
* Running time is independent of the byte sequences compared, making
|
||
* this safe to use for comparing secret values such as cryptographic
|
||
* MACs. In contrast, memcmp() may short-circuit after finding the first
|
||
* differing byte.
|
||
*
|
||
* timingsafe_memcmp n=0 661 picoseconds
|
||
* timingsafe_memcmp n=1 1 ns/byte 590 mb/s
|
||
* timingsafe_memcmp n=2 1 ns/byte 738 mb/s
|
||
* timingsafe_memcmp n=3 1 ns/byte 805 mb/s
|
||
* timingsafe_memcmp n=4 1 ns/byte 843 mb/s
|
||
* timingsafe_memcmp n=5 1 ns/byte 922 mb/s
|
||
* timingsafe_memcmp n=6 1 ns/byte 932 mb/s
|
||
* timingsafe_memcmp n=7 1 ns/byte 939 mb/s
|
||
* timingsafe_memcmp n=8 992 ps/byte 984 mb/s
|
||
* timingsafe_memcmp n=9 992 ps/byte 984 mb/s
|
||
* timingsafe_memcmp n=15 926 ps/byte 1,054 mb/s
|
||
* timingsafe_memcmp n=16 950 ps/byte 1,026 mb/s
|
||
* timingsafe_memcmp n=17 933 ps/byte 1,045 mb/s
|
||
* timingsafe_memcmp n=31 896 ps/byte 1,089 mb/s
|
||
* timingsafe_memcmp n=32 888 ps/byte 1,098 mb/s
|
||
* timingsafe_memcmp n=33 972 ps/byte 1,004 mb/s
|
||
* timingsafe_memcmp n=80 913 ps/byte 1,068 mb/s
|
||
* timingsafe_memcmp n=128 891 ps/byte 1,095 mb/s
|
||
* timingsafe_memcmp n=256 873 ps/byte 1,118 mb/s
|
||
* timingsafe_memcmp n=16384 858 ps/byte 1,138 mb/s
|
||
* timingsafe_memcmp n=32768 856 ps/byte 1,140 mb/s
|
||
* timingsafe_memcmp n=131072 857 ps/byte 1,138 mb/s
|
||
* bcmp ne n=256 3 ps/byte 246 gb/s
|
||
* bcmp eq n=256 32 ps/byte 30,233 mb/s
|
||
* memcmp ne n=256 3 ps/byte 246 gb/s
|
||
* memcmp eq n=256 31 ps/byte 31,493 mb/s
|
||
* timingsafe_bcmp ne n=256 27 ps/byte 35,992 mb/s
|
||
* timingsafe_bcmp eq n=256 27 ps/byte 35,992 mb/s
|
||
* timingsafe_memcmp ne n=256 877 ps/byte 1,113 mb/s
|
||
* timingsafe_memcmp eq n=256 883 ps/byte 1,105 mb/s
|
||
*
|
||
* @note each byte is interpreted as unsigned char
|
||
* @return -1, 0, or 1 based on comparison
|
||
* @see timingsafe_bcmp() it's 100x faster
|
||
* @asyncsignalsafe
|
||
*/
|
||
int timingsafe_memcmp(const void *p, const void *q, size_t n) {
|
||
const unsigned char *p1 = p, *p2 = q;
|
||
size_t i;
|
||
int res = 0, done = 0;
|
||
for (i = 0; i < n; 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;
|
||
}
|