/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ 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/intrin/likely.h"
#include "libc/dce.h"
#include "libc/nexgen32e/x86feature.h"
#include "libc/str/str.h"
#define PMOVMSKB(x) __builtin_ia32_pmovmskb128(x)
typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(1)));
static dontinline antiquity int memcmp_sse(const unsigned char *p,
const unsigned char *q, size_t n) {
unsigned u;
if (n > 32) {
while (n > 16 + 16) {
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
n -= 16;
p += 16;
q += 16;
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
}
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
if (!(u = PMOVMSKB(*(xmm_t *)(p + n - 16) == *(xmm_t *)(q + n - 16)) ^
0xffff)) {
return 0;
} else {
u = __builtin_ctzl(u);
return p[n - 16 + u] - q[n - 16 + u];
}
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
microarchitecture("avx") static int memcmp_avx(const unsigned char *p,
const unsigned char *q,
size_t n) {
uint64_t w;
unsigned u;
if (n > 32) {
while (n >= 16 + 64) {
w = (uint64_t)PMOVMSKB(((xmm_t *)p)[0] == ((xmm_t *)q)[0]) << 000 |
(uint64_t)PMOVMSKB(((xmm_t *)p)[1] == ((xmm_t *)q)[1]) << 020 |
(uint64_t)PMOVMSKB(((xmm_t *)p)[2] == ((xmm_t *)q)[2]) << 040 |
(uint64_t)PMOVMSKB(((xmm_t *)p)[3] == ((xmm_t *)q)[3]) << 060;
if (w == -1) {
n -= 64;
p += 64;
q += 64;
} else {
w = __builtin_ctzll(w ^ -1);
return p[w] - q[w];
}
}
while (n > 16 + 16) {
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
n -= 16;
p += 16;
q += 16;
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
}
if (!(u = PMOVMSKB(*(xmm_t *)p == *(xmm_t *)q) ^ 0xffff)) {
if (!(u = PMOVMSKB(*(xmm_t *)(p + n - 16) == *(xmm_t *)(q + n - 16)) ^
0xffff)) {
return 0;
} else {
u = __builtin_ctzl(u);
return p[n - 16 + u] - q[n - 16 + u];
}
} else {
u = __builtin_ctzl(u);
return p[u] - q[u];
}
}
/**
* Compares memory byte by byte.
*
* memcmp n=0 992 picoseconds
* memcmp n=1 1 ns/byte 738 mb/s
* memcmp n=2 661 ps/byte 1,476 mb/s
* memcmp n=3 551 ps/byte 1,771 mb/s
* memcmp n=4 248 ps/byte 3,936 mb/s
* memcmp n=5 198 ps/byte 4,920 mb/s
* memcmp n=6 165 ps/byte 5,904 mb/s
* memcmp n=7 141 ps/byte 6,889 mb/s
* memcmp n=8 124 ps/byte 7,873 mb/s
* memcmp n=9 110 ps/byte 8,857 mb/s
* memcmp n=15 44 ps/byte 22,143 mb/s
* memcmp n=16 41 ps/byte 23,619 mb/s
* memcmp n=17 77 ps/byte 12,547 mb/s
* memcmp n=31 42 ps/byte 22,881 mb/s
* memcmp n=32 41 ps/byte 23,619 mb/s
* memcmp n=33 60 ps/byte 16,238 mb/s
* memcmp n=80 53 ps/byte 18,169 mb/s
* memcmp n=128 38 ps/byte 25,194 mb/s
* memcmp n=256 32 ps/byte 30,233 mb/s
* memcmp n=16384 27 ps/byte 35,885 mb/s
* memcmp n=32768 29 ps/byte 32,851 mb/s
* memcmp n=131072 33 ps/byte 28,983 mb/s
*
* @return unsigned char subtraction at stop index
* @asyncsignalsafe
*/
int memcmp(const void *a, const void *b, size_t n) {
int c;
unsigned u;
uint32_t k, i, j;
uint64_t w, x, y;
const unsigned char *p, *q;
if ((p = a) == (q = b) || !n) return 0;
if ((c = *p - *q)) return c;
if (!IsTiny()) {
if (n <= 16) {
if (n >= 8) {
if (!(w = (x = ((uint64_t)p[0] << 000 | (uint64_t)p[1] << 010 |
(uint64_t)p[2] << 020 | (uint64_t)p[3] << 030 |
(uint64_t)p[4] << 040 | (uint64_t)p[5] << 050 |
(uint64_t)p[6] << 060 | (uint64_t)p[7] << 070)) ^
(y = ((uint64_t)q[0] << 000 | (uint64_t)q[1] << 010 |
(uint64_t)q[2] << 020 | (uint64_t)q[3] << 030 |
(uint64_t)q[4] << 040 | (uint64_t)q[5] << 050 |
(uint64_t)q[6] << 060 | (uint64_t)q[7] << 070)))) {
p += n - 8;
q += n - 8;
if (!(w = (x = ((uint64_t)p[0] << 000 | (uint64_t)p[1] << 010 |
(uint64_t)p[2] << 020 | (uint64_t)p[3] << 030 |
(uint64_t)p[4] << 040 | (uint64_t)p[5] << 050 |
(uint64_t)p[6] << 060 | (uint64_t)p[7] << 070)) ^
(y = ((uint64_t)q[0] << 000 | (uint64_t)q[1] << 010 |
(uint64_t)q[2] << 020 | (uint64_t)q[3] << 030 |
(uint64_t)q[4] << 040 | (uint64_t)q[5] << 050 |
(uint64_t)q[6] << 060 | (uint64_t)q[7] << 070)))) {
return 0;
}
}
u = __builtin_ctzll(w);
u = u & -8;
return ((x >> u) & 255) - ((y >> u) & 255);
} else if (n >= 4) {
if (!(k = (i = ((uint32_t)p[0] << 000 | (uint32_t)p[1] << 010 |
(uint32_t)p[2] << 020 | (uint32_t)p[3] << 030)) ^
(j = ((uint32_t)q[0] << 000 | (uint32_t)q[1] << 010 |
(uint32_t)q[2] << 020 | (uint32_t)q[3] << 030)))) {
p += n - 4;
q += n - 4;
if (!(k = (i = ((uint32_t)p[0] << 000 | (uint32_t)p[1] << 010 |
(uint32_t)p[2] << 020 | (uint32_t)p[3] << 030)) ^
(j = ((uint32_t)q[0] << 000 | (uint32_t)q[1] << 010 |
(uint32_t)q[2] << 020 | (uint32_t)q[3] << 030)))) {
return 0;
}
}
u = __builtin_ctzl(k);
u = u & -8;
return ((i >> u) & 255) - ((j >> u) & 255);
}
} else if (LIKELY(X86_HAVE(AVX))) {
return memcmp_avx(p, q, n);
} else {
return memcmp_sse(p, q, n);
}
}
for (; n; ++p, ++q, --n) {
if ((c = *p - *q)) {
return c;
}
}
return 0;
}