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@danlark1

danlark1/crc_strange_value.h Secret

Created Mar 8, 2021
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static const uint64_t zalign(16) poly[] = { 0x01db710641, 0x01f7011641 };
// ^^^^^^^^^^^^
// No use of poly
// ...
// x0, x1, x2, x3 are 128 bit registers
x3 = _mm_setr_epi32(~0, 0, ~0, 0); // Set reverse, i.e. bits from 0 to 31 are 1s, from 32 to 63 are zeros, etc
// No reassignment of x3
// ...
/*
* Barret reduce to 32-bits.
*/
x0 = _mm_load_si128((__m128i*)poly); // Load 16 bytes
x2 = _mm_and_si128(x1, x3); // Do logical AND with x3
x2 = _mm_clmulepi64_si128(x2, x0, 0x10); // Do CLMUL with the high 8 bytes of poly
x2 = _mm_and_si128(x2, x3); // Do logical AND with x3
x2 = _mm_clmulepi64_si128(x2, x0, 0x00); // Do CLMUL with the low 8 bytes of poly
x1 = _mm_xor_si128(x1, x2); // XOR x1 and x2
/*
* Return the crc32.
*/
return _mm_extract_epi32(x1, 1); // Return bytes from 4 to 8 of x1, i.e. extract the second 32 bit integer
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