diff --git a/src/nnue/layers/affine_transform_sparse_input.h b/src/nnue/layers/affine_transform_sparse_input.h
index cbeb507f..248e19dd 100644
--- a/src/nnue/layers/affine_transform_sparse_input.h
+++ b/src/nnue/layers/affine_transform_sparse_input.h
@@ -38,17 +38,99 @@
 namespace Stockfish::Eval::NNUE::Layers {
 
 #if (USE_SSSE3 | (USE_NEON >= 8))
-alignas(CacheLineSize) static inline const
-  std::array<std::array<std::uint16_t, 8>, 256> lookup_indices = []() {
-      std::array<std::array<std::uint16_t, 8>, 256> v{};
-      for (unsigned i = 0; i < 256; ++i)
-      {
-          std::uint64_t j = i, k = 0;
-          while (j)
-              v[i][k++] = pop_lsb(j);
-      }
-      return v;
-  }();
+
+    #if (USE_SSE41)
+alignas(CacheLineSize) static constexpr std::uint8_t
+    #else
+alignas(CacheLineSize) static constexpr std::uint16_t
+    #endif
+  lookup_indices[256][8] = {
+    {0, 0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0, 0}, {1, 0, 0, 0, 0, 0, 0, 0},
+    {0, 1, 0, 0, 0, 0, 0, 0}, {2, 0, 0, 0, 0, 0, 0, 0}, {0, 2, 0, 0, 0, 0, 0, 0},
+    {1, 2, 0, 0, 0, 0, 0, 0}, {0, 1, 2, 0, 0, 0, 0, 0}, {3, 0, 0, 0, 0, 0, 0, 0},
+    {0, 3, 0, 0, 0, 0, 0, 0}, {1, 3, 0, 0, 0, 0, 0, 0}, {0, 1, 3, 0, 0, 0, 0, 0},
+    {2, 3, 0, 0, 0, 0, 0, 0}, {0, 2, 3, 0, 0, 0, 0, 0}, {1, 2, 3, 0, 0, 0, 0, 0},
+    {0, 1, 2, 3, 0, 0, 0, 0}, {4, 0, 0, 0, 0, 0, 0, 0}, {0, 4, 0, 0, 0, 0, 0, 0},
+    {1, 4, 0, 0, 0, 0, 0, 0}, {0, 1, 4, 0, 0, 0, 0, 0}, {2, 4, 0, 0, 0, 0, 0, 0},
+    {0, 2, 4, 0, 0, 0, 0, 0}, {1, 2, 4, 0, 0, 0, 0, 0}, {0, 1, 2, 4, 0, 0, 0, 0},
+    {3, 4, 0, 0, 0, 0, 0, 0}, {0, 3, 4, 0, 0, 0, 0, 0}, {1, 3, 4, 0, 0, 0, 0, 0},
+    {0, 1, 3, 4, 0, 0, 0, 0}, {2, 3, 4, 0, 0, 0, 0, 0}, {0, 2, 3, 4, 0, 0, 0, 0},
+    {1, 2, 3, 4, 0, 0, 0, 0}, {0, 1, 2, 3, 4, 0, 0, 0}, {5, 0, 0, 0, 0, 0, 0, 0},
+    {0, 5, 0, 0, 0, 0, 0, 0}, {1, 5, 0, 0, 0, 0, 0, 0}, {0, 1, 5, 0, 0, 0, 0, 0},
+    {2, 5, 0, 0, 0, 0, 0, 0}, {0, 2, 5, 0, 0, 0, 0, 0}, {1, 2, 5, 0, 0, 0, 0, 0},
+    {0, 1, 2, 5, 0, 0, 0, 0}, {3, 5, 0, 0, 0, 0, 0, 0}, {0, 3, 5, 0, 0, 0, 0, 0},
+    {1, 3, 5, 0, 0, 0, 0, 0}, {0, 1, 3, 5, 0, 0, 0, 0}, {2, 3, 5, 0, 0, 0, 0, 0},
+    {0, 2, 3, 5, 0, 0, 0, 0}, {1, 2, 3, 5, 0, 0, 0, 0}, {0, 1, 2, 3, 5, 0, 0, 0},
+    {4, 5, 0, 0, 0, 0, 0, 0}, {0, 4, 5, 0, 0, 0, 0, 0}, {1, 4, 5, 0, 0, 0, 0, 0},
+    {0, 1, 4, 5, 0, 0, 0, 0}, {2, 4, 5, 0, 0, 0, 0, 0}, {0, 2, 4, 5, 0, 0, 0, 0},
+    {1, 2, 4, 5, 0, 0, 0, 0}, {0, 1, 2, 4, 5, 0, 0, 0}, {3, 4, 5, 0, 0, 0, 0, 0},
+    {0, 3, 4, 5, 0, 0, 0, 0}, {1, 3, 4, 5, 0, 0, 0, 0}, {0, 1, 3, 4, 5, 0, 0, 0},
+    {2, 3, 4, 5, 0, 0, 0, 0}, {0, 2, 3, 4, 5, 0, 0, 0}, {1, 2, 3, 4, 5, 0, 0, 0},
+    {0, 1, 2, 3, 4, 5, 0, 0}, {6, 0, 0, 0, 0, 0, 0, 0}, {0, 6, 0, 0, 0, 0, 0, 0},
+    {1, 6, 0, 0, 0, 0, 0, 0}, {0, 1, 6, 0, 0, 0, 0, 0}, {2, 6, 0, 0, 0, 0, 0, 0},
+    {0, 2, 6, 0, 0, 0, 0, 0}, {1, 2, 6, 0, 0, 0, 0, 0}, {0, 1, 2, 6, 0, 0, 0, 0},
+    {3, 6, 0, 0, 0, 0, 0, 0}, {0, 3, 6, 0, 0, 0, 0, 0}, {1, 3, 6, 0, 0, 0, 0, 0},
+    {0, 1, 3, 6, 0, 0, 0, 0}, {2, 3, 6, 0, 0, 0, 0, 0}, {0, 2, 3, 6, 0, 0, 0, 0},
+    {1, 2, 3, 6, 0, 0, 0, 0}, {0, 1, 2, 3, 6, 0, 0, 0}, {4, 6, 0, 0, 0, 0, 0, 0},
+    {0, 4, 6, 0, 0, 0, 0, 0}, {1, 4, 6, 0, 0, 0, 0, 0}, {0, 1, 4, 6, 0, 0, 0, 0},
+    {2, 4, 6, 0, 0, 0, 0, 0}, {0, 2, 4, 6, 0, 0, 0, 0}, {1, 2, 4, 6, 0, 0, 0, 0},
+    {0, 1, 2, 4, 6, 0, 0, 0}, {3, 4, 6, 0, 0, 0, 0, 0}, {0, 3, 4, 6, 0, 0, 0, 0},
+    {1, 3, 4, 6, 0, 0, 0, 0}, {0, 1, 3, 4, 6, 0, 0, 0}, {2, 3, 4, 6, 0, 0, 0, 0},
+    {0, 2, 3, 4, 6, 0, 0, 0}, {1, 2, 3, 4, 6, 0, 0, 0}, {0, 1, 2, 3, 4, 6, 0, 0},
+    {5, 6, 0, 0, 0, 0, 0, 0}, {0, 5, 6, 0, 0, 0, 0, 0}, {1, 5, 6, 0, 0, 0, 0, 0},
+    {0, 1, 5, 6, 0, 0, 0, 0}, {2, 5, 6, 0, 0, 0, 0, 0}, {0, 2, 5, 6, 0, 0, 0, 0},
+    {1, 2, 5, 6, 0, 0, 0, 0}, {0, 1, 2, 5, 6, 0, 0, 0}, {3, 5, 6, 0, 0, 0, 0, 0},
+    {0, 3, 5, 6, 0, 0, 0, 0}, {1, 3, 5, 6, 0, 0, 0, 0}, {0, 1, 3, 5, 6, 0, 0, 0},
+    {2, 3, 5, 6, 0, 0, 0, 0}, {0, 2, 3, 5, 6, 0, 0, 0}, {1, 2, 3, 5, 6, 0, 0, 0},
+    {0, 1, 2, 3, 5, 6, 0, 0}, {4, 5, 6, 0, 0, 0, 0, 0}, {0, 4, 5, 6, 0, 0, 0, 0},
+    {1, 4, 5, 6, 0, 0, 0, 0}, {0, 1, 4, 5, 6, 0, 0, 0}, {2, 4, 5, 6, 0, 0, 0, 0},
+    {0, 2, 4, 5, 6, 0, 0, 0}, {1, 2, 4, 5, 6, 0, 0, 0}, {0, 1, 2, 4, 5, 6, 0, 0},
+    {3, 4, 5, 6, 0, 0, 0, 0}, {0, 3, 4, 5, 6, 0, 0, 0}, {1, 3, 4, 5, 6, 0, 0, 0},
+    {0, 1, 3, 4, 5, 6, 0, 0}, {2, 3, 4, 5, 6, 0, 0, 0}, {0, 2, 3, 4, 5, 6, 0, 0},
+    {1, 2, 3, 4, 5, 6, 0, 0}, {0, 1, 2, 3, 4, 5, 6, 0}, {7, 0, 0, 0, 0, 0, 0, 0},
+    {0, 7, 0, 0, 0, 0, 0, 0}, {1, 7, 0, 0, 0, 0, 0, 0}, {0, 1, 7, 0, 0, 0, 0, 0},
+    {2, 7, 0, 0, 0, 0, 0, 0}, {0, 2, 7, 0, 0, 0, 0, 0}, {1, 2, 7, 0, 0, 0, 0, 0},
+    {0, 1, 2, 7, 0, 0, 0, 0}, {3, 7, 0, 0, 0, 0, 0, 0}, {0, 3, 7, 0, 0, 0, 0, 0},
+    {1, 3, 7, 0, 0, 0, 0, 0}, {0, 1, 3, 7, 0, 0, 0, 0}, {2, 3, 7, 0, 0, 0, 0, 0},
+    {0, 2, 3, 7, 0, 0, 0, 0}, {1, 2, 3, 7, 0, 0, 0, 0}, {0, 1, 2, 3, 7, 0, 0, 0},
+    {4, 7, 0, 0, 0, 0, 0, 0}, {0, 4, 7, 0, 0, 0, 0, 0}, {1, 4, 7, 0, 0, 0, 0, 0},
+    {0, 1, 4, 7, 0, 0, 0, 0}, {2, 4, 7, 0, 0, 0, 0, 0}, {0, 2, 4, 7, 0, 0, 0, 0},
+    {1, 2, 4, 7, 0, 0, 0, 0}, {0, 1, 2, 4, 7, 0, 0, 0}, {3, 4, 7, 0, 0, 0, 0, 0},
+    {0, 3, 4, 7, 0, 0, 0, 0}, {1, 3, 4, 7, 0, 0, 0, 0}, {0, 1, 3, 4, 7, 0, 0, 0},
+    {2, 3, 4, 7, 0, 0, 0, 0}, {0, 2, 3, 4, 7, 0, 0, 0}, {1, 2, 3, 4, 7, 0, 0, 0},
+    {0, 1, 2, 3, 4, 7, 0, 0}, {5, 7, 0, 0, 0, 0, 0, 0}, {0, 5, 7, 0, 0, 0, 0, 0},
+    {1, 5, 7, 0, 0, 0, 0, 0}, {0, 1, 5, 7, 0, 0, 0, 0}, {2, 5, 7, 0, 0, 0, 0, 0},
+    {0, 2, 5, 7, 0, 0, 0, 0}, {1, 2, 5, 7, 0, 0, 0, 0}, {0, 1, 2, 5, 7, 0, 0, 0},
+    {3, 5, 7, 0, 0, 0, 0, 0}, {0, 3, 5, 7, 0, 0, 0, 0}, {1, 3, 5, 7, 0, 0, 0, 0},
+    {0, 1, 3, 5, 7, 0, 0, 0}, {2, 3, 5, 7, 0, 0, 0, 0}, {0, 2, 3, 5, 7, 0, 0, 0},
+    {1, 2, 3, 5, 7, 0, 0, 0}, {0, 1, 2, 3, 5, 7, 0, 0}, {4, 5, 7, 0, 0, 0, 0, 0},
+    {0, 4, 5, 7, 0, 0, 0, 0}, {1, 4, 5, 7, 0, 0, 0, 0}, {0, 1, 4, 5, 7, 0, 0, 0},
+    {2, 4, 5, 7, 0, 0, 0, 0}, {0, 2, 4, 5, 7, 0, 0, 0}, {1, 2, 4, 5, 7, 0, 0, 0},
+    {0, 1, 2, 4, 5, 7, 0, 0}, {3, 4, 5, 7, 0, 0, 0, 0}, {0, 3, 4, 5, 7, 0, 0, 0},
+    {1, 3, 4, 5, 7, 0, 0, 0}, {0, 1, 3, 4, 5, 7, 0, 0}, {2, 3, 4, 5, 7, 0, 0, 0},
+    {0, 2, 3, 4, 5, 7, 0, 0}, {1, 2, 3, 4, 5, 7, 0, 0}, {0, 1, 2, 3, 4, 5, 7, 0},
+    {6, 7, 0, 0, 0, 0, 0, 0}, {0, 6, 7, 0, 0, 0, 0, 0}, {1, 6, 7, 0, 0, 0, 0, 0},
+    {0, 1, 6, 7, 0, 0, 0, 0}, {2, 6, 7, 0, 0, 0, 0, 0}, {0, 2, 6, 7, 0, 0, 0, 0},
+    {1, 2, 6, 7, 0, 0, 0, 0}, {0, 1, 2, 6, 7, 0, 0, 0}, {3, 6, 7, 0, 0, 0, 0, 0},
+    {0, 3, 6, 7, 0, 0, 0, 0}, {1, 3, 6, 7, 0, 0, 0, 0}, {0, 1, 3, 6, 7, 0, 0, 0},
+    {2, 3, 6, 7, 0, 0, 0, 0}, {0, 2, 3, 6, 7, 0, 0, 0}, {1, 2, 3, 6, 7, 0, 0, 0},
+    {0, 1, 2, 3, 6, 7, 0, 0}, {4, 6, 7, 0, 0, 0, 0, 0}, {0, 4, 6, 7, 0, 0, 0, 0},
+    {1, 4, 6, 7, 0, 0, 0, 0}, {0, 1, 4, 6, 7, 0, 0, 0}, {2, 4, 6, 7, 0, 0, 0, 0},
+    {0, 2, 4, 6, 7, 0, 0, 0}, {1, 2, 4, 6, 7, 0, 0, 0}, {0, 1, 2, 4, 6, 7, 0, 0},
+    {3, 4, 6, 7, 0, 0, 0, 0}, {0, 3, 4, 6, 7, 0, 0, 0}, {1, 3, 4, 6, 7, 0, 0, 0},
+    {0, 1, 3, 4, 6, 7, 0, 0}, {2, 3, 4, 6, 7, 0, 0, 0}, {0, 2, 3, 4, 6, 7, 0, 0},
+    {1, 2, 3, 4, 6, 7, 0, 0}, {0, 1, 2, 3, 4, 6, 7, 0}, {5, 6, 7, 0, 0, 0, 0, 0},
+    {0, 5, 6, 7, 0, 0, 0, 0}, {1, 5, 6, 7, 0, 0, 0, 0}, {0, 1, 5, 6, 7, 0, 0, 0},
+    {2, 5, 6, 7, 0, 0, 0, 0}, {0, 2, 5, 6, 7, 0, 0, 0}, {1, 2, 5, 6, 7, 0, 0, 0},
+    {0, 1, 2, 5, 6, 7, 0, 0}, {3, 5, 6, 7, 0, 0, 0, 0}, {0, 3, 5, 6, 7, 0, 0, 0},
+    {1, 3, 5, 6, 7, 0, 0, 0}, {0, 1, 3, 5, 6, 7, 0, 0}, {2, 3, 5, 6, 7, 0, 0, 0},
+    {0, 2, 3, 5, 6, 7, 0, 0}, {1, 2, 3, 5, 6, 7, 0, 0}, {0, 1, 2, 3, 5, 6, 7, 0},
+    {4, 5, 6, 7, 0, 0, 0, 0}, {0, 4, 5, 6, 7, 0, 0, 0}, {1, 4, 5, 6, 7, 0, 0, 0},
+    {0, 1, 4, 5, 6, 7, 0, 0}, {2, 4, 5, 6, 7, 0, 0, 0}, {0, 2, 4, 5, 6, 7, 0, 0},
+    {1, 2, 4, 5, 6, 7, 0, 0}, {0, 1, 2, 4, 5, 6, 7, 0}, {3, 4, 5, 6, 7, 0, 0, 0},
+    {0, 3, 4, 5, 6, 7, 0, 0}, {1, 3, 4, 5, 6, 7, 0, 0}, {0, 1, 3, 4, 5, 6, 7, 0},
+    {2, 3, 4, 5, 6, 7, 0, 0}, {0, 2, 3, 4, 5, 6, 7, 0}, {1, 2, 3, 4, 5, 6, 7, 0},
+    {0, 1, 2, 3, 4, 5, 6, 7}};
 
 // Find indices of nonzero numbers in an int32_t array
 template<const IndexType InputDimensions>
@@ -74,7 +156,11 @@ void find_nnz(const std::int32_t* input, std::uint16_t* out, IndexType& count_ou
     using vec128_t = __m128i;
         #define vec128_zero _mm_setzero_si128()
         #define vec128_set_16(a) _mm_set1_epi16(a)
-        #define vec128_load(a) _mm_load_si128(a)
+        #if (USE_SSE41)
+            #define vec128_load(a) _mm_cvtepu8_epi16(_mm_loadl_epi64(a))
+        #else
+            #define vec128_load(a) _mm_load_si128(a)
+        #endif
         #define vec128_storeu(a, b) _mm_storeu_si128(a, b)
         #define vec128_add(a, b) _mm_add_epi16(a, b)
     #elif defined(USE_NEON)