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NEON: simplify updates in NNUE accumulator

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Reduce # instructions using widening add/sub calls on AArch64.
Add shims for 32-bit ARM.

Passed non-regression STC:
https://tests.stockfishchess.org/tests/view/69c093d3f690a4b7f5fb0d6e
LLR: 5.15 (-2.94,2.94) <-1.75,0.25>
Total: 338624 W: 86931 L: 86853 D: 164840
Ptnml(0-2): 667, 35888, 96079, 36056, 622

closes https://github.com/official-stockfish/Stockfish/pull/6692

No functional change
This commit is contained in:
Linmiao Xu
2026-04-02 20:32:43 +02:00
committed by Disservin
parent c41c9bb973
commit 171afd2b4d
2 changed files with 9 additions and 8 deletions
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src/nnue/nnue_accumulator.cpp
+6 -6
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@@ -379,8 +379,8 @@ struct AccumulatorUpdateContext {
#ifdef USE_NEON
for (IndexType k = 0; k < Tiling::NumRegs; k += 2)
{
acc[k] = vec_sub_16(acc[k], vmovl_s8(vget_low_s8(column[k / 2])));
acc[k + 1] = vec_sub_16(acc[k + 1], vmovl_high_s8(column[k / 2]));
acc[k] = vsubw_s8(acc[k], vget_low_s8(column[k / 2]));
acc[k + 1] = vsubw_high_s8(acc[k + 1], column[k / 2]);
}
#else
for (IndexType k = 0; k < Tiling::NumRegs; ++k)
@@ -397,8 +397,8 @@ struct AccumulatorUpdateContext {
#ifdef USE_NEON
for (IndexType k = 0; k < Tiling::NumRegs; k += 2)
{
acc[k] = vec_add_16(acc[k], vmovl_s8(vget_low_s8(column[k / 2])));
acc[k + 1] = vec_add_16(acc[k + 1], vmovl_high_s8(column[k / 2]));
acc[k] = vaddw_s8(acc[k], vget_low_s8(column[k / 2]));
acc[k + 1] = vaddw_high_s8(acc[k + 1], column[k / 2]);
}
#else
for (IndexType k = 0; k < Tiling::NumRegs; ++k)
@@ -890,8 +890,8 @@ void update_threats_accumulator_full(Color persp
#ifdef USE_NEON
for (IndexType k = 0; k < Tiling::NumRegs; k += 2)
{
acc[k] = vec_add_16(acc[k], vmovl_s8(vget_low_s8(column[k / 2])));
acc[k + 1] = vec_add_16(acc[k + 1], vmovl_high_s8(column[k / 2]));
acc[k] = vaddw_s8(acc[k], vget_low_s8(column[k / 2]));
acc[k + 1] = vaddw_high_s8(acc[k + 1], column[k / 2]);
}
#else
for (IndexType k = 0; k < Tiling::NumRegs; ++k)