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Feature #22463 » fastmemchr.c

watson1978 (Shizuo Fujita), 10/22/2026 04:24 AM

 
#include <stdint.h>
#include <string.h>
#include <emmintrin.h>

#define ONES UINT64_C(0x0101010101010101)
#define HIGHS UINT64_C(0x8080808080808080)
#define HASZERO(x) (((x) - ONES) & ~(x) & HIGHS)

__declspec(dllexport) void *swar_memchr(const void *s, int c, size_t n) {
const unsigned char *p = s;
uint64_t k = ONES * (unsigned char)c;
while (n >= 8) {
uint64_t v;
memcpy(&v, p, 8);
uint64_t m = HASZERO(v ^ k);
if (m) return (void *)(p + (__builtin_ctzll(m) >> 3));
p += 8;
n -= 8;
}
for (; n; p++, n--) if (*p == (unsigned char)c) return (void *)p;
return NULL;
}

__declspec(dllexport) void *sse2_memchr(const void *s, int c, size_t n) {
const unsigned char *p = s;
__m128i needle = _mm_set1_epi8((char)c);
while (n >= 16) {
int mask = _mm_movemask_epi8(_mm_cmpeq_epi8(_mm_loadu_si128((const __m128i *)p), needle));
if (mask) return (void *)(p + __builtin_ctz(mask));
p += 16;
n -= 16;
}
for (; n; p++, n--) if (*p == (unsigned char)c) return (void *)p;
return NULL;
}
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