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avx512bw-strstr-v3.cpp
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avx512bw-strstr-v3.cpp
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// implements scheme described in http://0x80.pl/articles/simd-friendly-karp-rabin.html
size_t avx512bw_strstr_v3_anysize(const char* string, size_t n, const char* needle, size_t k) {
assert(n > 0);
assert(k > 0);
const __m512i first = _mm512_set1_epi8(needle[0]);
const __m512i last = _mm512_set1_epi8(needle[k - 1]);
char* haystack = const_cast<char*>(string);
char* end = haystack + n;
for (/**/; haystack < end; haystack += 64) {
const __m512i block_first = _mm512_loadu_si512(haystack + 0);
const __mmask64 first_eq = _mm512_cmpeq_epi8_mask(block_first, first);
if (first_eq == 0)
continue;
const __m512i block_last = _mm512_loadu_si512(haystack + k - 1);
uint64_t mask = _mm512_mask_cmpeq_epi8_mask(first_eq, block_last, last);
while (mask != 0) {
const uint64_t bitpos = bits::get_first_bit_set(mask);
const char* s = reinterpret_cast<const char*>(haystack);
if (memcmp(s + bitpos + 1, needle + 1, k - 2) == 0) {
return (s - string) + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return size_t(-1);
}
template <size_t k, typename MEMCMP>
size_t avx512bw_strstr_v3_memcmp(const char* string, size_t n, const char* needle, MEMCMP memeq_fun) {
assert(n > 0);
assert(k > 0);
const __m512i first = _mm512_set1_epi8(needle[0]);
const __m512i last = _mm512_set1_epi8(needle[k - 1]);
char* haystack = const_cast<char*>(string);
char* end = haystack + n;
for (/**/; haystack < end; haystack += 64) {
const __m512i block_first = _mm512_loadu_si512(haystack + 0);
const __mmask64 first_eq = _mm512_cmpeq_epi8_mask(block_first, first);
if (first_eq == 0)
continue;
const __m512i block_last = _mm512_loadu_si512(haystack + k - 1);
uint64_t mask = _mm512_mask_cmpeq_epi8_mask(first_eq, block_last, last);
while (mask != 0) {
const uint64_t bitpos = bits::get_first_bit_set(mask);
const char* s = reinterpret_cast<const char*>(haystack);
if (memeq_fun(s + bitpos + 1, needle + 1)) {
return (s - string) + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return size_t(-1);
}
// ------------------------------------------------------------------------
size_t avx512bw_strstr_v3(const char* s, size_t n, const char* needle, size_t k) {
size_t result = std::string::npos;
if (n < k) {
return result;
}
switch (k) {
case 0:
return 0;
case 1: {
const char* res = reinterpret_cast<const char*>(strchr(s, needle[0]));
return (res != nullptr) ? res - s : std::string::npos;
}
case 2:
result = avx512bw_strstr_v3_memcmp<2>(s, n, needle, always_true);
break;
case 3:
result = avx512bw_strstr_v3_memcmp<3>(s, n, needle, memcmp1);
break;
case 4:
result = avx512bw_strstr_v3_memcmp<4>(s, n, needle, memcmp2);
break;
case 5:
result = avx512bw_strstr_v3_memcmp<5>(s, n, needle, memcmp3);
break;
case 6:
result = avx512bw_strstr_v3_memcmp<6>(s, n, needle, memcmp4);
break;
case 7:
result = avx512bw_strstr_v3_memcmp<7>(s, n, needle, memcmp5);
break;
case 8:
result = avx512bw_strstr_v3_memcmp<8>(s, n, needle, memcmp6);
break;
case 9:
result = avx512bw_strstr_v3_memcmp<9>(s, n, needle, memcmp7);
break;
case 10:
result = avx512bw_strstr_v3_memcmp<10>(s, n, needle, memcmp8);
break;
case 11:
result = avx512bw_strstr_v3_memcmp<11>(s, n, needle, memcmp9);
break;
case 12:
result = avx512bw_strstr_v3_memcmp<12>(s, n, needle, memcmp10);
break;
default:
result = avx512bw_strstr_v3_anysize(s, n, needle, k);
break;
}
if (result <= n - k) {
return result;
} else {
return std::string::npos;
}
}
// --------------------------------------------------
size_t avx512bw_strstr_v3(const std::string& s, const std::string& needle) {
return avx512bw_strstr_v3(s.data(), s.size(), needle.data(), needle.size());
}