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simplify find_nnz a bit

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This code path is never taken for vector sizes >= 512, so we can simplify it.

closes https://github.com/official-stockfish/Stockfish/pull/6501

No functional change
This commit is contained in:
anematode
2026-01-01 16:08:03 +01:00
committed by Joost VandeVondele
parent 0317c6ccec
commit 593eeaf24c
1 changed files with 11 additions and 14 deletions
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src/nnue/layers/affine_transform_sparse_input.h
+6 -9
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@@ -138,11 +138,12 @@ void find_nnz(const std::int32_t* RESTRICT input,
using namespace SIMD;
constexpr IndexType InputSimdWidth = sizeof(vec_uint_t) / sizeof(std::int32_t);
// Inputs are processed InputSimdWidth at a time and outputs are processed 8 at a time so we process in chunks of max(InputSimdWidth, 8)
constexpr IndexType ChunkSize = std::max<IndexType>(InputSimdWidth, 8);
// Outputs are processed 8 elements at a time, even if the SIMD width is narrower
constexpr IndexType ChunkSize = 8;
constexpr IndexType NumChunks = InputDimensions / ChunkSize;
constexpr IndexType InputsPerChunk = ChunkSize / InputSimdWidth;
constexpr IndexType OutputsPerChunk = ChunkSize / 8;
static_assert(InputsPerChunk > 0 && "SIMD width too wide");
const auto inputVector = reinterpret_cast<const vec_uint_t*>(input);
IndexType count = 0;
@@ -157,16 +158,12 @@ void find_nnz(const std::int32_t* RESTRICT input,
const vec_uint_t inputChunk = inputVector[i * InputsPerChunk + j];
nnz |= unsigned(vec_nnz(inputChunk)) << (j * InputSimdWidth);
}
for (IndexType j = 0; j < OutputsPerChunk; ++j)
{
const unsigned lookup = (nnz >> (j * 8)) & 0xFF;
const vec128_t offsets =
vec128_load(reinterpret_cast<const vec128_t*>(&Lookup.offset_indices[lookup]));
vec128_load(reinterpret_cast<const vec128_t*>(&Lookup.offset_indices[nnz]));
vec128_storeu(reinterpret_cast<vec128_t*>(out + count), vec128_add(base, offsets));
count += popcount(lookup);
count += popcount(nnz);
base = vec128_add(base, increment);
}
}
count_out = count;
#endif
}