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Use arithmetic right shift for sign extension in MMX and SSE2 paths

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This appears to be slightly faster than using a comparison against zero
to compute the high bits, on both old (like Pentium III) and new (like
Zen 2) hardware.

closes https://github.com/official-stockfish/Stockfish/pull/3254

No functional change.
This commit is contained in:
Fanael Linithien 2020-12-07 14:46:29 +01:00 • committed by Joost VandeVondele
parent 8630d03dd4
commit c7f0a768cb
1 changed files with 4 additions and 6 deletions
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10
src/nnue/layers/affine_transform.h
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@ -680,9 +680,8 @@ namespace Eval::NNUE::Layers {
for (IndexType j = 0; j < kNumChunks; ++j) {
__m128i row_j = _mm_load_si128(&row[j]);
__m128i input_j = _mm_load_si128(&input_vector[j]);
__m128i row_signs = _mm_cmpgt_epi8(kZeros, row_j);
__m128i extended_row_lo = _mm_unpacklo_epi8(row_j, row_signs);
__m128i extended_row_hi = _mm_unpackhi_epi8(row_j, row_signs);
__m128i extended_row_lo = _mm_srai_epi16(_mm_unpacklo_epi8(row_j, row_j), 8);
__m128i extended_row_hi = _mm_srai_epi16(_mm_unpackhi_epi8(row_j, row_j), 8);
__m128i extended_input_lo = _mm_unpacklo_epi8(input_j, kZeros);
__m128i extended_input_hi = _mm_unpackhi_epi8(input_j, kZeros);
__m128i product_lo = _mm_madd_epi16(extended_row_lo, extended_input_lo);
@ -704,9 +703,8 @@ namespace Eval::NNUE::Layers {
for (IndexType j = 0; j < kNumChunks; ++j) {
__m64 row_j = row[j];
__m64 input_j = input_vector[j];
__m64 row_signs = _mm_cmpgt_pi8(kZeros, row_j);
__m64 extended_row_lo = _mm_unpacklo_pi8(row_j, row_signs);
__m64 extended_row_hi = _mm_unpackhi_pi8(row_j, row_signs);
__m64 extended_row_lo = _mm_srai_pi16(_mm_unpacklo_pi8(row_j, row_j), 8);
__m64 extended_row_hi = _mm_srai_pi16(_mm_unpackhi_pi8(row_j, row_j), 8);
__m64 extended_input_lo = _mm_unpacklo_pi8(input_j, kZeros);
__m64 extended_input_hi = _mm_unpackhi_pi8(input_j, kZeros);
__m64 product_lo = _mm_madd_pi16(extended_row_lo, extended_input_lo);