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Make memchr() and memccpy() faster

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Justine Tunney 2024-09-30 05:54:34 -07:00
parent fef24d622a
commit e4d6eb382a
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GPG key ID: BE714B4575D6E328
3 changed files with 95 additions and 24 deletions
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39
libc/intrin/memchr.c
View file

@ -19,10 +19,10 @@
#include "libc/dce.h"
#include "libc/nexgen32e/x86feature.h"
#include "libc/str/str.h"
#include "third_party/aarch64/arm_neon.internal.h"
#include "third_party/intel/immintrin.internal.h"
#ifndef __aarch64__
typedef char xmm_t __attribute__((__vector_size__(16), __aligned__(1)));
static inline const unsigned char *memchr_pure(const unsigned char *s,
unsigned char c, size_t n) {
size_t i;
@ -35,22 +35,27 @@ static inline const unsigned char *memchr_pure(const unsigned char *s,
}
#if defined(__x86_64__) && !defined(__chibicc__)
static __vex const unsigned char *memchr_sse(const unsigned char *s,
unsigned char c, size_t n) {
size_t i;
unsigned m;
xmm_t v, t = {c, c, c, c, c, c, c, c, c, c, c, c, c, c, c, c};
for (; n >= 16; n -= 16, s += 16) {
v = *(const xmm_t *)s;
m = __builtin_ia32_pmovmskb128(v == t);
if (m) {
m = __builtin_ctzll(m);
return s + m;
}
static const char *memchr_sse(const char *s, char c, size_t n) {
const char *e = s + n;
__m128i t = _mm_set1_epi8(c);
unsigned m, k = (uintptr_t)s & 15;
m = _mm_movemask_epi8(
_mm_cmpeq_epi8(_mm_load_si128((const __m128i *)((uintptr_t)s & -16)), t));
m >>= k;
if (m) {
s += __builtin_ctz(m);
if (s < e)
return s;
return 0;
}
for (i = 0; i < n; ++i) {
if (s[i] == c) {
return s + i;
for (s += 16 - k; s < e; s += 16) {
m = _mm_movemask_epi8(
_mm_cmpeq_epi8(_mm_load_si128((const __m128i *)s), t));
if (m) {
s += __builtin_ctz(m);
if (s < e)
return s;
return 0;
}
}
return 0;

15
libc/str/memccpy.c
View file

@ -45,13 +45,14 @@
* @asyncsignalsafe
*/
void *memccpy(void *dst, const void *src, int c, size_t n) {
char *d;
size_t i;
const char *s;
for (d = dst, s = src, i = 0; i < n; ++i) {
if (((d[i] = s[i]) & 255) == (c & 255)) {
return d + i + 1;
}
const char *p;
// this memchr() call is only correct if your memchr() implementation
// offers the same readahead safety guarantees as cosmopolitan's does
if ((p = memchr(src, c, n))) {
size_t m = p + 1 - (const char *)src;
memmove(dst, src, m);
return (char *)dst + m;
}
memmove(dst, src, n);
return 0;
}