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sse4.2-strstr.cpp
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sse4.2-strstr.cpp
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/* Usage of PCMPESTRM instruction from SSE 4.1 */
size_t FORCE_INLINE sse42_strstr_anysize(const char* s, size_t n, const char* needle, size_t k) {
assert(k > 0);
assert(n > 0);
const __m128i N = _mm_loadu_si128((__m128i*)needle);
for (size_t i = 0; i < n; i += 16) {
const int mode = _SIDD_UBYTE_OPS
| _SIDD_CMP_EQUAL_ORDERED
| _SIDD_BIT_MASK;
const __m128i D = _mm_loadu_si128((__m128i*)(s + i));
const __m128i res = _mm_cmpestrm(N, k, D, n - i, mode);
uint64_t mask = _mm_cvtsi128_si64(res);
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask);
// we know that at least the first character of needle matches
if (memcmp(s + i + bitpos + 1, needle + 1, k - 1) == 0) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
template <size_t k, typename MEMCMP>
size_t FORCE_INLINE sse42_strstr_memcmp(const char* s, size_t n, const char* needle, MEMCMP memcmp_fun) {
assert(k > 0);
assert(n > 0);
const __m128i N = _mm_loadu_si128((__m128i*)needle);
for (size_t i = 0; i < n; i += 16) {
const int mode = _SIDD_UBYTE_OPS
| _SIDD_CMP_EQUAL_ORDERED
| _SIDD_BIT_MASK;
const __m128i D = _mm_loadu_si128((__m128i*)(s + i));
const __m128i res = _mm_cmpestrm(N, k, D, n - i, mode);
uint64_t mask = _mm_cvtsi128_si64(res);
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask);
if (memcmp_fun(s + i + bitpos + 1, needle + 1)) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t sse42_strstr(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 = sse42_strstr_memcmp<2>(s, n, needle, memcmp1);
break;
case 3:
result = sse42_strstr_memcmp<3>(s, n, needle, memcmp2);
break;
case 4:
result = sse42_strstr_memcmp<4>(s, n, needle, memcmp3);
break;
case 5:
result = sse42_strstr_memcmp<5>(s, n, needle, memcmp4);
break;
case 6:
result = sse42_strstr_memcmp<6>(s, n, needle, memcmp5);
break;
case 7:
result = sse42_strstr_memcmp<7>(s, n, needle, memcmp6);
break;
case 8:
result = sse42_strstr_memcmp<8>(s, n, needle, memcmp7);
break;
case 9:
result = sse42_strstr_memcmp<9>(s, n, needle, memcmp8);
break;
case 10:
result = sse42_strstr_memcmp<10>(s, n, needle, memcmp9);
break;
case 11:
result = sse42_strstr_memcmp<11>(s, n, needle, memcmp10);
break;
case 12:
result = sse42_strstr_memcmp<12>(s, n, needle, memcmp11);
break;
default:
result = sse42_strstr_anysize(s, n, needle, k);
break;
}
if (result <= n - k) {
return result;
} else {
return std::string::npos;
}
}
// ------------------------------------------------------------------------
size_t sse42_strstr(const std::string& s, const std::string& needle) {
return sse42_strstr(s.data(), s.size(), needle.data(), needle.size());
}