#include #include #include #include #include // g++ -march=icelake-client // Requires SSSE3 for `pshufb` and GFNI(+AVX512VL) for `vgf2p8affineqb` __m128i BitReverse( __m128i Input ) { return _mm_shuffle_epi8( // Step 2: Reverse the order of the bytes themselves _mm_gf2p8affine_epi64_epi8( // Step 1: Reverse each of the within each byte Input, _mm_set1_epi64x( // The 8x8 binary-matrix, defined as a 64-bit value (8x8=64) // I've broken up the binary values with "'" characters so that // you may see the individual rows of the 8x8 matrix // This is the same as: // [ 1 0 0 0 0 0 0 0 ] < Byte 7, Bit 0 // [ 0 1 0 0 0 0 0 0 ] < Byte 6, Bit 1 // [ 0 0 1 0 0 0 0 0 ] < Byte 5, Bit 2 // X' = [ 0 0 0 1 0 0 0 0 ] < Byte 4, Bit 3 * X + 0 // [ 0 0 0 0 1 0 0 0 ] < Byte 3, Bit 4 // [ 0 0 0 0 0 1 0 0 ] < Byte 2, Bit 5 // [ 0 0 0 0 0 0 1 0 ] < Byte 1, Bit 6 // [ 0 0 0 0 0 0 0 1 ] < Byte 0, Bit 7 0b10000000'01000000'00100000'00010000'00001000'00000100'00000010'00000001 ), 0 // We don't care to do a final `xor` to the result, so keep this 0 ), _mm_set_epi8(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15) // Reverse byte-indices ); } void Print( __m128i Input ) { std::printf( "%.64s%.64s\n", std::bitset<64>(_mm_cvtsi128_si64(Input )).to_string().c_str(), std::bitset<64>(_mm_extract_epi64(Input,1)).to_string().c_str() ); } int main() { __m128i TestVec = _mm_set_epi64x(0xBEEFBEEFBEEFBEEFull,0xDEADDEADDEADDEADull); Print(TestVec); Print(BitReverse(TestVec)); } // Output: // 11011110101011011101111010101101110111101010110111011110101011011011111011101111101111101110111110111110111011111011111011101111 // 11110111011111011111011101111101111101110111110111110111011111011011010101111011101101010111101110110101011110111011010101111011

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