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sse4-strstr-unrolled.cpp
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sse4-strstr-unrolled.cpp
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// Note: it appears that these specialized functions do not help.
// But I decided to left them, just in case.
// use functions/templates dealing with certain substring length
//#define ENABLE_SSE4_LENGTH_SPECIALIZATIONS
// When defined use sse4_strstr_unrolled_memcmp template,
// otherwise use just sse4_strstr_unrolled_max20 and sse4_strstr_unrolled_max36
//#define ENABLE_SSE4_MEMCMP_TEMPLATES
size_t sse4_strstr_unrolled_anysize(const char* s, size_t n, const char* needle, size_t needle_size) {
assert(needle_size > 4);
assert(n > 0);
const __m128i prefix = _mm_loadu_si128(reinterpret_cast<const __m128i*>(needle));
const __m128i zeros = _mm_setzero_si128();
__m128i prev = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s));
__m128i curr;
for (size_t i = 0; i < n; i += 16) {
curr = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i + 16));
const __m128i data0 = prev;
const __m128i data1 = _mm_alignr_epi8(curr, prev, 8);
const __m128i result0 = _mm_mpsadbw_epu8(data0, prefix, 0);
const __m128i result1 = _mm_mpsadbw_epu8(data1, prefix, 0);
prev = curr;
const __m128i result = _mm_packus_epi16(result0, result1);
const __m128i cmp = _mm_cmpeq_epi8(result, zeros);
unsigned mask = _mm_movemask_epi8(cmp);
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask);
if (memcmp(s + i + bitpos + 4, needle + 4, needle_size - 4) == 0) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
template <size_t k, typename MEMCMP>
size_t sse4_strstr_unrolled_memcmp(const char* s, size_t n, const char* needle, MEMCMP memcmp_fun) {
assert(k > 4);
assert(n > 0);
const __m128i prefix = _mm_loadu_si128(reinterpret_cast<const __m128i*>(needle));
const __m128i zeros = _mm_setzero_si128();
__m128i prev = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s));
__m128i curr;
for (size_t i = 0; i < n; i += 16) {
curr = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i + 16));
const __m128i data0 = prev;
const __m128i data1 = _mm_alignr_epi8(curr, prev, 8);
const __m128i result0 = _mm_mpsadbw_epu8(data0, prefix, 0);
const __m128i result1 = _mm_mpsadbw_epu8(data1, prefix, 0);
prev = curr;
const __m128i result = _mm_packus_epi16(result0, result1);
const __m128i cmp = _mm_cmpeq_epi8(result, zeros);
unsigned mask = _mm_movemask_epi8(cmp);
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask);
if (memcmp_fun(s + i + bitpos + 4, needle + 4)) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t sse4_strstr_unrolled_max20(const char* s, size_t n, const char* needle, size_t needle_size) {
const __m128i zeros = _mm_setzero_si128();
const __m128i prefix = sse::load(needle);
const __m128i suffix = sse::load(needle + 4);
const __m128i suff_mask = sse::mask_lower_bytes(needle_size - 4);
for (size_t i = 0; i < n; i += 8) {
const __m128i data = sse::load(s + i);
const __m128i result = _mm_mpsadbw_epu8(data, prefix, 0);
const __m128i cmp = _mm_cmpeq_epi16(result, zeros);
unsigned mask = _mm_movemask_epi8(cmp) & 0x5555;
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask)/2;
const __m128i str = sse::load(s + i + bitpos + 4);
const __m128i cmp = _mm_cmpeq_epi8(str, suffix);
if (_mm_testc_si128(cmp, suff_mask)) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t sse4_strstr_unrolled_max36(const char* s, size_t n, const char* needle, size_t needle_size) {
const __m128i zeros = _mm_setzero_si128();
const __m128i prefix = sse::load(needle);
const __m128i suffix1 = sse::load(needle + 4);
const __m128i suffix2 = sse::load(needle + 16 + 4);
const __m128i suff_mask = sse::mask_higher_bytes(needle_size - (16 + 4));
for (size_t i = 0; i < n; i += 8) {
const __m128i data = sse::load(s + i);
const __m128i result = _mm_mpsadbw_epu8(data, prefix, 0);
const __m128i cmp = _mm_cmpeq_epi16(result, zeros);
unsigned mask = _mm_movemask_epi8(cmp) & 0x5555;
while (mask != 0) {
const auto bitpos = bits::get_first_bit_set(mask)/2;
const __m128i c1 = _mm_cmpeq_epi8(sse::load(s + i + bitpos + 4), suffix1);
const __m128i c2 = _mm_cmpeq_epi8(sse::load(s + i + bitpos + 16 + 4), suffix2);
const __m128i c3 = _mm_or_si128(c2, suff_mask);
const __m128i tmp = _mm_and_si128(c1, c3);
if (_mm_movemask_epi8(tmp) == 0xffff) {
return i + bitpos;
}
mask = bits::clear_leftmost_set(mask);
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t sse4_strstr_unrolled_len3(const char* s, size_t n, const char* needle) {
const __m128i prefix = _mm_loadu_si128(reinterpret_cast<const __m128i*>(needle));
const __m128i zeros = _mm_setzero_si128();
for (size_t i = 0; i < n; i += 8) {
const __m128i data = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i));
const __m128i lastbyte = _mm_cvtepu8_epi16(_mm_srli_si128(data, 3));
const __m128i result = _mm_mpsadbw_epu8(data, prefix, 0);
const __m128i cmp = _mm_cmpeq_epi16(_mm_sub_epi16(result, lastbyte), zeros);
unsigned mask = _mm_movemask_epi8(cmp) & 0x5555;
if (mask != 0) {
return i + bits::get_first_bit_set(mask)/2;
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t sse4_strstr_unrolled_len4(const char* s, size_t n, const char* needle) {
const __m128i prefix = _mm_loadu_si128(reinterpret_cast<const __m128i*>(needle));
const __m128i zeros = _mm_setzero_si128();
for (size_t i = 0; i < n; i += 8) {
const __m128i data = _mm_loadu_si128(reinterpret_cast<const __m128i*>(s + i));
const __m128i result = _mm_mpsadbw_epu8(data, prefix, 0);
const __m128i cmp = _mm_cmpeq_epi16(result, zeros);
unsigned mask = _mm_movemask_epi8(cmp);
if (mask != 0) {
return i + bits::get_first_bit_set(mask)/2;
}
}
return std::string::npos;
}
// ------------------------------------------------------------------------
size_t sse4_strstr_unrolled(const char* s, size_t n, const char* needle, size_t needle_size) {
size_t result = std::string::npos;
if (n < needle_size) {
return result;
}
switch (needle_size) {
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: {
const char* res = reinterpret_cast<const char*>(strstr(s, needle));
return (res != nullptr) ? res - s : std::string::npos;
}
case 3:
result = sse4_strstr_unrolled_len3(s, n, needle);
break;
case 4:
result = sse4_strstr_unrolled_len4(s, n, needle);
break;
#ifdef ENABLE_SSE4_LENGTH_SPECIALIZATIONS
#ifdef ENABLE_SSE4_MEMCMP_TEMPLATES
case 5:
result = sse4_strstr_unrolled_memcmp<5>(s, n, needle, memcmp1);
break;
case 6:
result = sse4_strstr_unrolled_memcmp<6>(s, n, needle, memcmp2);
break;
case 7:
result = sse4_strstr_unrolled_memcmp<7>(s, n, needle, memcmp3);
break;
case 8:
result = sse4_strstr_unrolled_memcmp<8>(s, n, needle, memcmp4);
break;
case 9:
result = sse4_strstr_unrolled_memcmp<9>(s, n, needle, memcmp5);
break;
case 10:
result = sse4_strstr_unrolled_memcmp<10>(s, n, needle, memcmp6);
break;
case 11:
result = sse4_strstr_unrolled_memcmp<11>(s, n, needle, memcmp7);
break;
case 12:
result = sse4_strstr_unrolled_memcmp<12>(s, n, needle, memcmp8);
break;
case 13:
result = sse4_strstr_unrolled_memcmp<13>(s, n, needle, memcmp9);
break;
case 14:
result = sse4_strstr_unrolled_memcmp<14>(s, n, needle, memcmp10);
break;
#else
case 5: case 6: case 7: case 8:
case 9: case 10: case 11: case 12:
case 13: case 14: /* 5 .. 14 */
#endif // ENABLE_SSE4_MEMCMP_TEMPLATES
case 15: case 16: case 17: case 18: case 19:
case 20: /* 15..20 */
result = sse4_strstr_unrolled_max20(s, n, needle, needle_size);
break;
case 21: case 22: case 23: case 24: case 25:
case 26: case 27: case 28: case 29: case 30:
case 31: case 32: case 33: case 34: case 35:
case 36: /* 21..36 */
result = sse4_strstr_unrolled_max36(s, n, needle, needle_size);
break;
#endif // ENABLE_SSE4_LENGTH_SPECIALIZATIONS
default:
result = sse4_strstr_unrolled_anysize(s, n, needle, needle_size);
break;
}
if (result <= n - needle_size) {
return result;
} else {
return std::string::npos;
}
}
// --------------------------------------------------
size_t sse4_strstr_unrolled(const std::string& s, const std::string& needle) {
return sse4_strstr_unrolled(s.data(), s.size(), needle.data(), needle.size());
}