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avx2-strstr.cpp
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avx2-strstr.cpp
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size_t avx2_strstr_long(const char* s, size_t n, const char* neddle, size_t neddle_size) {
assert(neddle_size > 4);
assert(n > 0);
const uint32_t prefix32 = *reinterpret_cast<const uint32_t*>(neddle);
const __m256i prefix = _mm256_set1_epi32(prefix32);
const __m256i zeros = _mm256_setzero_si256();
const __m256i permute = _mm256_setr_epi32(
0, 1, 2, 0,
2, 3, 4, 0
);
for (size_t i = 0; i < n; i += 16) {
const __m256i in = _mm256_loadu_si256(reinterpret_cast<const __m256i*>(s + i));
/*
[00|01|02|03|04|05|06|07|08|09|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31]
lane | boundary
[00|01|02|03|04|05|06|07|08|09|10|11|??|??|??|??|08|09|10|11|12|13|14|15|16|17|18|19|??|??|??|??]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
*/
const __m256i data = _mm256_permutevar8x32_epi32(in, permute);
const __m256i result = _mm256_mpsadbw_epu8(data, prefix, 0);
const __m256i cmp = _mm256_cmpeq_epi16(result, zeros);
uint32_t mask = _mm256_movemask_epi8(cmp) & 0x55555555u;
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask)/2;
if (memcmp(s + i + bitpos + 4, neddle + 4, neddle_size - 4) == 0) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t avx2_strstr_len4(const char* s, size_t n, const char* neddle) {
assert(n > 0);
const uint32_t prefix32 = *reinterpret_cast<const uint32_t*>(neddle);
const __m256i prefix = _mm256_set1_epi32(prefix32);
const __m256i zeros = _mm256_setzero_si256();
const __m256i permute = _mm256_setr_epi32(
0, 1, 2, 0,
2, 3, 4, 0
);
for (size_t i = 0; i < n; i += 16) {
const __m256i in = _mm256_loadu_si256(reinterpret_cast<const __m256i*>(s + i));
const __m256i data = _mm256_permutevar8x32_epi32(in, permute);
const __m256i result = _mm256_mpsadbw_epu8(data, prefix, 0);
const __m256i cmp = _mm256_cmpeq_epi16(result, zeros);
const uint32_t mask = _mm256_movemask_epi8(cmp) & 0x55555555u;
if (mask != 0) {
return i + bits::get_first_bit_set(mask)/2;
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t avx2_strstr(const char* s, size_t n, const char* neddle, size_t neddle_size) {
size_t result = std::string::npos;
if (n < neddle_size) {
return result;
}
switch (neddle_size) {
case 0:
return 0;
case 1: {
const char* res = reinterpret_cast<const char*>(strchr(s, neddle[0]));
return (res != nullptr) ? res - s : std::string::npos;
}
case 2:
case 3:
{
const char* res = reinterpret_cast<const char*>(strstr(s, neddle));
return (res != nullptr) ? res - s : std::string::npos;
}
case 4:
result = avx2_strstr_len4(s, n, neddle);
break;
default:
result = avx2_strstr_long(s, n, neddle, neddle_size);
break;
}
if (result <= n - neddle_size) {
return result;
} else {
return std::string::npos;
}
}
// --------------------------------------------------
size_t avx2_strstr(const std::string& s, const std::string& neddle) {
return avx2_strstr(s.data(), s.size(), neddle.data(), neddle.size());
}