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x86: Apply half tabular method in _mm_crc32 family #1185

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May 22, 2024
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x86: Apply half tabular method in _mm_crc32 family #1185

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20 changes: 14 additions & 6 deletions simde/x86/sse4.2.h
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Original file line number Diff line number Diff line change
Expand Up @@ -300,12 +300,20 @@ simde_mm_crc32_u8(uint32_t prevcrc, uint8_t v) {
#else
uint32_t crc = prevcrc;
crc ^= v;
for(int bit = 0 ; bit < 8 ; bit++) {
if (crc & 1)
crc = (crc >> 1) ^ UINT32_C(0x82f63b78);
else
crc = (crc >> 1);
}
// Adapted from: https://create.stephan-brumme.com/crc32/
// Apply half-byte comparision algorithm for the best ratio between
// performance and lookup table.

// The lookup table just needs to store every 16th entry
// of the standard look-up table.
static const uint32_t crc32_half_byte_tbl[] = {
0x00000000, 0x105ec76f, 0x20bd8ede, 0x30e349b1, 0x417b1dbc, 0x5125dad3,
0x61c69362, 0x7198540d, 0x82f63b78, 0x92a8fc17, 0xa24bb5a6, 0xb21572c9,
0xc38d26c4, 0xd3d3e1ab, 0xe330a81a, 0xf36e6f75,
};

crc = (crc >> 4) ^ crc32_half_byte_tbl[crc & 0x0f];
crc = (crc >> 4) ^ crc32_half_byte_tbl[crc & 0x0f];
return crc;
#endif
#endif
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