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sse2-strstr.cpp
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sse2-strstr.cpp
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// implements scheme described in http://0x80.pl/articles/simd-friendly-karp-rabin.html
size_t FORCE_INLINE sse2_strstr_anysize(const char* s, size_t n, const char* needle, size_t k) {
assert(k > 0);
assert(n > 0);
const __m128i first = _mm_set1_epi8(needle[0]);
const __m128i last = _mm_set1_epi8(needle[k - 1]);
for (size_t i = 0; i < n; i += 16) {
const __m128i block_first = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i));
const __m128i block_last = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i + k - 1));
const __m128i eq_first = _mm_cmpeq_epi8(first, block_first);
const __m128i eq_last = _mm_cmpeq_epi8(last, block_last);
uint16_t mask = _mm_movemask_epi8(_mm_and_si128(eq_first, eq_last));
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask);
if (memcmp(s + i + bitpos + 1, needle + 1, k - 2) == 0) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
template <size_t k, typename MEMCMP>
size_t FORCE_INLINE sse2_strstr_memcmp(const char* s, size_t n, const char* needle, MEMCMP memcmp_fun) {
assert(k > 0);
assert(n > 0);
const __m128i first = _mm_set1_epi8(needle[0]);
const __m128i last = _mm_set1_epi8(needle[k - 1]);
for (size_t i = 0; i < n; i += 16) {
const __m128i block_first = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i));
const __m128i block_last = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i + k - 1));
const __m128i eq_first = _mm_cmpeq_epi8(first, block_first);
const __m128i eq_last = _mm_cmpeq_epi8(last, block_last);
uint32_t mask = _mm_movemask_epi8(_mm_and_si128(eq_first, eq_last));
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 sse2_strstr_v2(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 = sse2_strstr_memcmp<2>(s, n, needle, always_true);
break;
case 3:
result = sse2_strstr_memcmp<3>(s, n, needle, memcmp1);
break;
case 4:
result = sse2_strstr_memcmp<4>(s, n, needle, memcmp2);
break;
case 5:
result = sse2_strstr_memcmp<5>(s, n, needle, memcmp4);
break;
case 6:
result = sse2_strstr_memcmp<6>(s, n, needle, memcmp4);
break;
case 7:
result = sse2_strstr_memcmp<7>(s, n, needle, memcmp5);
break;
case 8:
result = sse2_strstr_memcmp<8>(s, n, needle, memcmp6);
break;
case 9:
result = sse2_strstr_memcmp<9>(s, n, needle, memcmp8);
break;
case 10:
result = sse2_strstr_memcmp<10>(s, n, needle, memcmp8);
break;
case 11:
result = sse2_strstr_memcmp<11>(s, n, needle, memcmp9);
break;
case 12:
result = sse2_strstr_memcmp<12>(s, n, needle, memcmp10);
break;
default:
result = sse2_strstr_anysize(s, n, needle, k);
break;
}
if (result <= n - k) {
return result;
} else {
return std::string::npos;
}
}
// ------------------------------------------------------------------------
size_t sse2_strstr_v2(const std::string& s, const std::string& needle) {
return sse2_strstr_v2(s.data(), s.size(), needle.data(), needle.size());
}