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upgrade horizontal sum in distance_single_code for PQ/IVFPQ #2830

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upgrade horizontal sum in distance_single_code for PQ/IVFPQ #2830

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31faaaf
Faster versions of fvec_op_ny_Dx for AVX2 (#2811)
alexanderguzhva Apr 24, 2023
7a8614c
upgrade horizontal sum in distance_single_code for PQ/IVFPQ
Apr 24, 2023
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26 changes: 12 additions & 14 deletions faiss/impl/code_distance/code_distance-avx2.h
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Original file line number Diff line number Diff line change
Expand Up @@ -17,21 +17,19 @@

namespace {

// Computes a horizontal sum over an __m256 register
inline float horizontal_sum(const __m256 reg) {
const __m256 h0 = _mm256_hadd_ps(reg, reg);
const __m256 h1 = _mm256_hadd_ps(h0, h0);

// extract high and low __m128 regs from __m256
const __m128 h2 = _mm256_extractf128_ps(h1, 1);
const __m128 h3 = _mm256_castps256_ps128(h1);

// get a final hsum into all 4 regs
const __m128 h4 = _mm_add_ss(h2, h3);
inline float horizontal_sum(const __m128 v) {
const __m128 v0 = _mm_shuffle_ps(v, v, _MM_SHUFFLE(0, 0, 3, 2));
const __m128 v1 = _mm_add_ps(v, v0);
__m128 v2 = _mm_shuffle_ps(v1, v1, _MM_SHUFFLE(0, 0, 0, 1));
const __m128 v3 = _mm_add_ps(v1, v2);
return _mm_cvtss_f32(v3);
}

// extract f[0] from __m128
const float hsum = _mm_cvtss_f32(h4);
return hsum;
// Computes a horizontal sum over an __m256 register
inline float horizontal_sum(const __m256 v) {
const __m128 v0 =
_mm_add_ps(_mm256_castps256_ps128(v), _mm256_extractf128_ps(v, 1));
return horizontal_sum(v0);
}

} // namespace
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