]> git.sesse.net Git - stockfish/blobdiff - src/nnue/nnue_feature_transformer.h
Merge remote-tracking branch 'upstream/master'
[stockfish] / src / nnue / nnue_feature_transformer.h
index 1cfebbe4cbe80425f65aa3e3012594494d615294..fa180678d89cd333bba382b83f463c64fe9d4958 100644 (file)
@@ -1,6 +1,6 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
-  Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)
+  Copyright (C) 2004-2024 The Stockfish developers (see AUTHORS file)
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
 #ifndef NNUE_FEATURE_TRANSFORMER_H_INCLUDED
 #define NNUE_FEATURE_TRANSFORMER_H_INCLUDED
 
-#include "nnue_common.h"
-#include "nnue_architecture.h"
-#include "features/index_list.h"
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstring>
+#include <iosfwd>
+#include <utility>
 
-#include <cstring> // std::memset()
+#include "../position.h"
+#include "../types.h"
+#include "nnue_accumulator.h"
+#include "nnue_architecture.h"
+#include "nnue_common.h"
 
-namespace Eval::NNUE {
+namespace Stockfish::Eval::NNUE {
+
+using BiasType       = std::int16_t;
+using WeightType     = std::int16_t;
+using PSQTWeightType = std::int32_t;
+
+// If vector instructions are enabled, we update and refresh the
+// accumulator tile by tile such that each tile fits in the CPU's
+// vector registers.
+#define VECTOR
+
+static_assert(PSQTBuckets % 8 == 0,
+              "Per feature PSQT values cannot be processed at granularity lower than 8 at a time.");
+
+#ifdef USE_AVX512
+using vec_t      = __m512i;
+using psqt_vec_t = __m256i;
+    #define vec_load(a) _mm512_load_si512(a)
+    #define vec_store(a, b) _mm512_store_si512(a, b)
+    #define vec_add_16(a, b) _mm512_add_epi16(a, b)
+    #define vec_sub_16(a, b) _mm512_sub_epi16(a, b)
+    #define vec_mulhi_16(a, b) _mm512_mulhi_epi16(a, b)
+    #define vec_zero() _mm512_setzero_epi32()
+    #define vec_set_16(a) _mm512_set1_epi16(a)
+    #define vec_max_16(a, b) _mm512_max_epi16(a, b)
+    #define vec_min_16(a, b) _mm512_min_epi16(a, b)
+    #define vec_slli_16(a, b) _mm512_slli_epi16(a, b)
+    // Inverse permuted at load time
+    #define vec_packus_16(a, b) _mm512_packus_epi16(a, b)
+    #define vec_load_psqt(a) _mm256_load_si256(a)
+    #define vec_store_psqt(a, b) _mm256_store_si256(a, b)
+    #define vec_add_psqt_32(a, b) _mm256_add_epi32(a, b)
+    #define vec_sub_psqt_32(a, b) _mm256_sub_epi32(a, b)
+    #define vec_zero_psqt() _mm256_setzero_si256()
+    #define NumRegistersSIMD 16
+    #define MaxChunkSize 64
+
+#elif USE_AVX2
+using vec_t      = __m256i;
+using psqt_vec_t = __m256i;
+    #define vec_load(a) _mm256_load_si256(a)
+    #define vec_store(a, b) _mm256_store_si256(a, b)
+    #define vec_add_16(a, b) _mm256_add_epi16(a, b)
+    #define vec_sub_16(a, b) _mm256_sub_epi16(a, b)
+    #define vec_mulhi_16(a, b) _mm256_mulhi_epi16(a, b)
+    #define vec_zero() _mm256_setzero_si256()
+    #define vec_set_16(a) _mm256_set1_epi16(a)
+    #define vec_max_16(a, b) _mm256_max_epi16(a, b)
+    #define vec_min_16(a, b) _mm256_min_epi16(a, b)
+    #define vec_slli_16(a, b) _mm256_slli_epi16(a, b)
+    // Inverse permuted at load time
+    #define vec_packus_16(a, b) _mm256_packus_epi16(a, b)
+    #define vec_load_psqt(a) _mm256_load_si256(a)
+    #define vec_store_psqt(a, b) _mm256_store_si256(a, b)
+    #define vec_add_psqt_32(a, b) _mm256_add_epi32(a, b)
+    #define vec_sub_psqt_32(a, b) _mm256_sub_epi32(a, b)
+    #define vec_zero_psqt() _mm256_setzero_si256()
+    #define NumRegistersSIMD 16
+    #define MaxChunkSize 32
+
+#elif USE_SSE2
+using vec_t      = __m128i;
+using psqt_vec_t = __m128i;
+    #define vec_load(a) (*(a))
+    #define vec_store(a, b) *(a) = (b)
+    #define vec_add_16(a, b) _mm_add_epi16(a, b)
+    #define vec_sub_16(a, b) _mm_sub_epi16(a, b)
+    #define vec_mulhi_16(a, b) _mm_mulhi_epi16(a, b)
+    #define vec_zero() _mm_setzero_si128()
+    #define vec_set_16(a) _mm_set1_epi16(a)
+    #define vec_max_16(a, b) _mm_max_epi16(a, b)
+    #define vec_min_16(a, b) _mm_min_epi16(a, b)
+    #define vec_slli_16(a, b) _mm_slli_epi16(a, b)
+    #define vec_packus_16(a, b) _mm_packus_epi16(a, b)
+    #define vec_load_psqt(a) (*(a))
+    #define vec_store_psqt(a, b) *(a) = (b)
+    #define vec_add_psqt_32(a, b) _mm_add_epi32(a, b)
+    #define vec_sub_psqt_32(a, b) _mm_sub_epi32(a, b)
+    #define vec_zero_psqt() _mm_setzero_si128()
+    #define NumRegistersSIMD (Is64Bit ? 16 : 8)
+    #define MaxChunkSize 16
+
+#elif USE_NEON
+using vec_t      = int16x8_t;
+using psqt_vec_t = int32x4_t;
+    #define vec_load(a) (*(a))
+    #define vec_store(a, b) *(a) = (b)
+    #define vec_add_16(a, b) vaddq_s16(a, b)
+    #define vec_sub_16(a, b) vsubq_s16(a, b)
+    #define vec_mulhi_16(a, b) vqdmulhq_s16(a, b)
+    #define vec_zero() \
+        vec_t { 0 }
+    #define vec_set_16(a) vdupq_n_s16(a)
+    #define vec_max_16(a, b) vmaxq_s16(a, b)
+    #define vec_min_16(a, b) vminq_s16(a, b)
+    #define vec_slli_16(a, b) vshlq_s16(a, vec_set_16(b))
+    #define vec_packus_16(a, b) reinterpret_cast<vec_t>(vcombine_u8(vqmovun_s16(a), vqmovun_s16(b)))
+    #define vec_load_psqt(a) (*(a))
+    #define vec_store_psqt(a, b) *(a) = (b)
+    #define vec_add_psqt_32(a, b) vaddq_s32(a, b)
+    #define vec_sub_psqt_32(a, b) vsubq_s32(a, b)
+    #define vec_zero_psqt() \
+        psqt_vec_t { 0 }
+    #define NumRegistersSIMD 16
+    #define MaxChunkSize 16
+
+#else
+    #undef VECTOR
+
+#endif
+
+
+#ifdef VECTOR
+
+    // Compute optimal SIMD register count for feature transformer accumulation.
+
+    // We use __m* types as template arguments, which causes GCC to emit warnings
+    // about losing some attribute information. This is irrelevant to us as we
+    // only take their size, so the following pragma are harmless.
+    #if defined(__GNUC__)
+        #pragma GCC diagnostic push
+        #pragma GCC diagnostic ignored "-Wignored-attributes"
+    #endif
+
+template<typename SIMDRegisterType, typename LaneType, int NumLanes, int MaxRegisters>
+static constexpr int BestRegisterCount() {
+    #define RegisterSize sizeof(SIMDRegisterType)
+    #define LaneSize sizeof(LaneType)
+
+    static_assert(RegisterSize >= LaneSize);
+    static_assert(MaxRegisters <= NumRegistersSIMD);
+    static_assert(MaxRegisters > 0);
+    static_assert(NumRegistersSIMD > 0);
+    static_assert(RegisterSize % LaneSize == 0);
+    static_assert((NumLanes * LaneSize) % RegisterSize == 0);
+
+    const int ideal = (NumLanes * LaneSize) / RegisterSize;
+    if (ideal <= MaxRegisters)
+        return ideal;
+
+    // Look for the largest divisor of the ideal register count that is smaller than MaxRegisters
+    for (int divisor = MaxRegisters; divisor > 1; --divisor)
+        if (ideal % divisor == 0)
+            return divisor;
+
+    return 1;
+}
+    #if defined(__GNUC__)
+        #pragma GCC diagnostic pop
+    #endif
+#endif
+
+
+// Input feature converter
+template<IndexType                                 TransformedFeatureDimensions,
+         Accumulator<TransformedFeatureDimensions> StateInfo::*accPtr>
+class FeatureTransformer {
 
-  // Input feature converter
-  class FeatureTransformer {
+    // Number of output dimensions for one side
+    static constexpr IndexType HalfDimensions = TransformedFeatureDimensions;
 
    private:
-    // Number of output dimensions for one side
-    static constexpr IndexType kHalfDimensions = kTransformedFeatureDimensions;
+#ifdef VECTOR
+    static constexpr int NumRegs =
+      BestRegisterCount<vec_t, WeightType, TransformedFeatureDimensions, NumRegistersSIMD>();
+    static constexpr int NumPsqtRegs =
+      BestRegisterCount<psqt_vec_t, PSQTWeightType, PSQTBuckets, NumRegistersSIMD>();
+
+    static constexpr IndexType TileHeight     = NumRegs * sizeof(vec_t) / 2;
+    static constexpr IndexType PsqtTileHeight = NumPsqtRegs * sizeof(psqt_vec_t) / 4;
+    static_assert(HalfDimensions % TileHeight == 0, "TileHeight must divide HalfDimensions");
+    static_assert(PSQTBuckets % PsqtTileHeight == 0, "PsqtTileHeight must divide PSQTBuckets");
+#endif
 
    public:
     // Output type
     using OutputType = TransformedFeatureType;
 
     // Number of input/output dimensions
-    static constexpr IndexType kInputDimensions = RawFeatures::kDimensions;
-    static constexpr IndexType kOutputDimensions = kHalfDimensions * 2;
+    static constexpr IndexType InputDimensions  = FeatureSet::Dimensions;
+    static constexpr IndexType OutputDimensions = HalfDimensions;
 
     // Size of forward propagation buffer
-    static constexpr std::size_t kBufferSize =
-        kOutputDimensions * sizeof(OutputType);
+    static constexpr std::size_t BufferSize = OutputDimensions * sizeof(OutputType);
 
     // Hash value embedded in the evaluation file
-    static constexpr std::uint32_t GetHashValue() {
-      return RawFeatures::kHashValue ^ kOutputDimensions;
+    static constexpr std::uint32_t get_hash_value() {
+        return FeatureSet::HashValue ^ (OutputDimensions * 2);
     }
 
-    // Read network parameters
-    bool ReadParameters(std::istream& stream) {
-      stream.read(reinterpret_cast<char*>(biases_),
-                  kHalfDimensions * sizeof(BiasType));
-      stream.read(reinterpret_cast<char*>(weights_),
-                  kHalfDimensions * kInputDimensions * sizeof(WeightType));
-      return !stream.fail();
+    static constexpr void order_packs([[maybe_unused]] uint64_t* v) {
+#if defined(USE_AVX512)  // _mm512_packs_epi16 ordering
+        uint64_t tmp0 = v[2], tmp1 = v[3];
+        v[2] = v[8], v[3] = v[9];
+        v[8] = v[4], v[9] = v[5];
+        v[4] = tmp0, v[5] = tmp1;
+        tmp0 = v[6], tmp1 = v[7];
+        v[6] = v[10], v[7] = v[11];
+        v[10] = v[12], v[11] = v[13];
+        v[12] = tmp0, v[13] = tmp1;
+#elif defined(USE_AVX2)  // _mm256_packs_epi16 ordering
+        std::swap(v[2], v[4]);
+        std::swap(v[3], v[5]);
+#endif
     }
 
-    // Proceed with the difference calculation if possible
-    bool UpdateAccumulatorIfPossible(const Position& pos) const {
-      const auto now = pos.state();
-      if (now->accumulator.computed_accumulation) {
-        return true;
-      }
-      const auto prev = now->previous;
-      if (prev && prev->accumulator.computed_accumulation) {
-        UpdateAccumulator(pos);
-        return true;
-      }
-      return false;
+    static constexpr void inverse_order_packs([[maybe_unused]] uint64_t* v) {
+#if defined(USE_AVX512)  // Inverse _mm512_packs_epi16 ordering
+        uint64_t tmp0 = v[2], tmp1 = v[3];
+        v[2] = v[4], v[3] = v[5];
+        v[4] = v[8], v[5] = v[9];
+        v[8] = tmp0, v[9] = tmp1;
+        tmp0 = v[6], tmp1 = v[7];
+        v[6] = v[12], v[7] = v[13];
+        v[12] = v[10], v[13] = v[11];
+        v[10] = tmp0, v[11] = tmp1;
+#elif defined(USE_AVX2)  // Inverse _mm256_packs_epi16 ordering
+        std::swap(v[2], v[4]);
+        std::swap(v[3], v[5]);
+#endif
     }
 
-    // Convert input features
-    void Transform(const Position& pos, OutputType* output, bool refresh) const {
-      if (refresh || !UpdateAccumulatorIfPossible(pos)) {
-        RefreshAccumulator(pos);
-      }
-      const auto& accumulation = pos.state()->accumulator.accumulation;
-
-  #if defined(USE_AVX2)
-      constexpr IndexType kNumChunks = kHalfDimensions / kSimdWidth;
-      constexpr int kControl = 0b11011000;
-      const __m256i kZero = _mm256_setzero_si256();
-
-  #elif defined(USE_SSSE3)
-      constexpr IndexType kNumChunks = kHalfDimensions / kSimdWidth;
-
-  #ifdef USE_SSE41
-      const __m128i kZero = _mm_setzero_si128();
-  #else
-      const __m128i k0x80s = _mm_set1_epi8(-128);
-  #endif
-
-  #elif defined(USE_NEON)
-      constexpr IndexType kNumChunks = kHalfDimensions / (kSimdWidth / 2);
-      const int8x8_t kZero = {0};
-  #endif
-
-      const Color perspectives[2] = {pos.side_to_move(), ~pos.side_to_move()};
-      for (IndexType p = 0; p < 2; ++p) {
-        const IndexType offset = kHalfDimensions * p;
-
-  #if defined(USE_AVX2)
-        auto out = reinterpret_cast<__m256i*>(&output[offset]);
-        for (IndexType j = 0; j < kNumChunks; ++j) {
-          __m256i sum0 =
-
-  #if defined(__MINGW32__) || defined(__MINGW64__)
-            // HACK: Use _mm256_loadu_si256() instead of _mm256_load_si256. Because the binary
-            //       compiled with g++ in MSYS2 crashes here because the output memory is not aligned
-            //       even though alignas is specified.
-            _mm256_loadu_si256
-  #else
-            _mm256_load_si256
-  #endif
-
-            (&reinterpret_cast<const __m256i*>(
-              accumulation[perspectives[p]][0])[j * 2 + 0]);
-          __m256i sum1 =
-
-  #if defined(__MINGW32__) || defined(__MINGW64__)
-            _mm256_loadu_si256
-  #else
-            _mm256_load_si256
-  #endif
-
-            (&reinterpret_cast<const __m256i*>(
-              accumulation[perspectives[p]][0])[j * 2 + 1]);
-
-  #if defined(__MINGW32__) || defined(__MINGW64__)
-          _mm256_storeu_si256
-  #else
-          _mm256_store_si256
-  #endif
-
-          (&out[j], _mm256_permute4x64_epi64(_mm256_max_epi8(
-              _mm256_packs_epi16(sum0, sum1), kZero), kControl));
+    void permute_weights([[maybe_unused]] void (*order_fn)(uint64_t*)) const {
+#if defined(USE_AVX2)
+    #if defined(USE_AVX512)
+        constexpr IndexType di = 16;
+    #else
+        constexpr IndexType di = 8;
+    #endif
+        uint64_t* b = reinterpret_cast<uint64_t*>(const_cast<BiasType*>(&biases[0]));
+        for (IndexType i = 0; i < HalfDimensions * sizeof(BiasType) / sizeof(uint64_t); i += di)
+            order_fn(&b[i]);
+
+        for (IndexType j = 0; j < InputDimensions; ++j)
+        {
+            uint64_t* w =
+              reinterpret_cast<uint64_t*>(const_cast<WeightType*>(&weights[j * HalfDimensions]));
+            for (IndexType i = 0; i < HalfDimensions * sizeof(WeightType) / sizeof(uint64_t);
+                 i += di)
+                order_fn(&w[i]);
         }
+#endif
+    }
 
-  #elif defined(USE_SSSE3)
-        auto out = reinterpret_cast<__m128i*>(&output[offset]);
-        for (IndexType j = 0; j < kNumChunks; ++j) {
-          __m128i sum0 = _mm_load_si128(&reinterpret_cast<const __m128i*>(
-              accumulation[perspectives[p]][0])[j * 2 + 0]);
-          __m128i sum1 = _mm_load_si128(&reinterpret_cast<const __m128i*>(
-              accumulation[perspectives[p]][0])[j * 2 + 1]);
-      const __m128i packedbytes = _mm_packs_epi16(sum0, sum1);
+    inline void scale_weights(bool read) const {
+        for (IndexType j = 0; j < InputDimensions; ++j)
+        {
+            WeightType* w = const_cast<WeightType*>(&weights[j * HalfDimensions]);
+            for (IndexType i = 0; i < HalfDimensions; ++i)
+                w[i] = read ? w[i] * 2 : w[i] / 2;
+        }
 
-          _mm_store_si128(&out[j],
+        BiasType* b = const_cast<BiasType*>(biases);
+        for (IndexType i = 0; i < HalfDimensions; ++i)
+            b[i] = read ? b[i] * 2 : b[i] / 2;
+    }
 
-  #ifdef USE_SSE41
-            _mm_max_epi8(packedbytes, kZero)
-  #else
-            _mm_subs_epi8(_mm_adds_epi8(packedbytes, k0x80s), k0x80s)
-  #endif
+    // Read network parameters
+    bool read_parameters(std::istream& stream) {
 
-          );
-        }
+        read_leb_128<BiasType>(stream, biases, HalfDimensions);
+        read_leb_128<WeightType>(stream, weights, HalfDimensions * InputDimensions);
+        read_leb_128<PSQTWeightType>(stream, psqtWeights, PSQTBuckets * InputDimensions);
 
-  #elif defined(USE_NEON)
-        const auto out = reinterpret_cast<int8x8_t*>(&output[offset]);
-        for (IndexType j = 0; j < kNumChunks; ++j) {
-          int16x8_t sum = reinterpret_cast<const int16x8_t*>(
-              accumulation[perspectives[p]][0])[j];
-          out[j] = vmax_s8(vqmovn_s16(sum), kZero);
-        }
+        permute_weights(inverse_order_packs);
+        scale_weights(true);
+        return !stream.fail();
+    }
 
-  #else
-        for (IndexType j = 0; j < kHalfDimensions; ++j) {
-          BiasType sum = accumulation[static_cast<int>(perspectives[p])][0][j];
-          output[offset + j] = static_cast<OutputType>(
-              std::max<int>(0, std::min<int>(127, sum)));
-        }
-  #endif
+    // Write network parameters
+    bool write_parameters(std::ostream& stream) const {
+
+        permute_weights(order_packs);
+        scale_weights(false);
 
-      }
+        write_leb_128<BiasType>(stream, biases, HalfDimensions);
+        write_leb_128<WeightType>(stream, weights, HalfDimensions * InputDimensions);
+        write_leb_128<PSQTWeightType>(stream, psqtWeights, PSQTBuckets * InputDimensions);
+
+        permute_weights(inverse_order_packs);
+        scale_weights(true);
+        return !stream.fail();
     }
 
-   private:
-    // Calculate cumulative value without using difference calculation
-    void RefreshAccumulator(const Position& pos) const {
-      auto& accumulator = pos.state()->accumulator;
-      IndexType i = 0;
-      Features::IndexList active_indices[2];
-      RawFeatures::AppendActiveIndices(pos, kRefreshTriggers[i],
-                                       active_indices);
-      for (Color perspective : { WHITE, BLACK }) {
-        std::memcpy(accumulator.accumulation[perspective][i], biases_,
-                   kHalfDimensions * sizeof(BiasType));
-        for (const auto index : active_indices[perspective]) {
-          const IndexType offset = kHalfDimensions * index;
-
-  #if defined(USE_AVX2)
-          auto accumulation = reinterpret_cast<__m256i*>(
-              &accumulator.accumulation[perspective][i][0]);
-          auto column = reinterpret_cast<const __m256i*>(&weights_[offset]);
-          constexpr IndexType kNumChunks = kHalfDimensions / (kSimdWidth / 2);
-          for (IndexType j = 0; j < kNumChunks; ++j) {
-  #if defined(__MINGW32__) || defined(__MINGW64__)
-            _mm256_storeu_si256(&accumulation[j], _mm256_add_epi16(_mm256_loadu_si256(&accumulation[j]), column[j]));
-  #else
-            accumulation[j] = _mm256_add_epi16(accumulation[j], column[j]);
-  #endif
-          }
-
-  #elif defined(USE_SSE2)
-          auto accumulation = reinterpret_cast<__m128i*>(
-              &accumulator.accumulation[perspective][i][0]);
-          auto column = reinterpret_cast<const __m128i*>(&weights_[offset]);
-          constexpr IndexType kNumChunks = kHalfDimensions / (kSimdWidth / 2);
-          for (IndexType j = 0; j < kNumChunks; ++j) {
-            accumulation[j] = _mm_add_epi16(accumulation[j], column[j]);
-          }
-
-  #elif defined(USE_NEON)
-          auto accumulation = reinterpret_cast<int16x8_t*>(
-              &accumulator.accumulation[perspective][i][0]);
-          auto column = reinterpret_cast<const int16x8_t*>(&weights_[offset]);
-          constexpr IndexType kNumChunks = kHalfDimensions / (kSimdWidth / 2);
-          for (IndexType j = 0; j < kNumChunks; ++j) {
-            accumulation[j] = vaddq_s16(accumulation[j], column[j]);
-          }
-
-  #else
-          for (IndexType j = 0; j < kHalfDimensions; ++j) {
-            accumulator.accumulation[perspective][i][j] += weights_[offset + j];
-          }
-  #endif
+    // Convert input features
+    std::int32_t transform(const Position&                           pos,
+                           AccumulatorCaches::Cache<HalfDimensions>* cache,
+                           OutputType*                               output,
+                           int                                       bucket) const {
+        update_accumulator<WHITE>(pos, cache);
+        update_accumulator<BLACK>(pos, cache);
+
+        const Color perspectives[2]  = {pos.side_to_move(), ~pos.side_to_move()};
+        const auto& psqtAccumulation = (pos.state()->*accPtr).psqtAccumulation;
+        const auto  psqt =
+          (psqtAccumulation[perspectives[0]][bucket] - psqtAccumulation[perspectives[1]][bucket])
+          / 2;
+
+        const auto& accumulation = (pos.state()->*accPtr).accumulation;
+
+        for (IndexType p = 0; p < 2; ++p)
+        {
+            const IndexType offset = (HalfDimensions / 2) * p;
+
+#if defined(VECTOR)
+
+            constexpr IndexType OutputChunkSize = MaxChunkSize;
+            static_assert((HalfDimensions / 2) % OutputChunkSize == 0);
+            constexpr IndexType NumOutputChunks = HalfDimensions / 2 / OutputChunkSize;
+
+            const vec_t Zero = vec_zero();
+            const vec_t One  = vec_set_16(127 * 2);
+
+            const vec_t* in0 = reinterpret_cast<const vec_t*>(&(accumulation[perspectives[p]][0]));
+            const vec_t* in1 =
+              reinterpret_cast<const vec_t*>(&(accumulation[perspectives[p]][HalfDimensions / 2]));
+            vec_t* out = reinterpret_cast<vec_t*>(output + offset);
+
+            // Per the NNUE architecture, here we want to multiply pairs of
+            // clipped elements and divide the product by 128. To do this,
+            // we can naively perform min/max operation to clip each of the
+            // four int16 vectors, mullo pairs together, then pack them into
+            // one int8 vector. However, there exists a faster way.
+
+            // The idea here is to use the implicit clipping from packus to
+            // save us two vec_max_16 instructions. This clipping works due
+            // to the fact that any int16 integer below zero will be zeroed
+            // on packus.
+
+            // Consider the case where the second element is negative.
+            // If we do standard clipping, that element will be zero, which
+            // means our pairwise product is zero. If we perform packus and
+            // remove the lower-side clip for the second element, then our
+            // product before packus will be negative, and is zeroed on pack.
+            // The two operation produce equivalent results, but the second
+            // one (using packus) saves one max operation per pair.
+
+            // But here we run into a problem: mullo does not preserve the
+            // sign of the multiplication. We can get around this by doing
+            // mulhi, which keeps the sign. But that requires an additional
+            // tweak.
+
+            // mulhi cuts off the last 16 bits of the resulting product,
+            // which is the same as performing a rightward shift of 16 bits.
+            // We can use this to our advantage. Recall that we want to
+            // divide the final product by 128, which is equivalent to a
+            // 7-bit right shift. Intuitively, if we shift the clipped
+            // value left by 9, and perform mulhi, which shifts the product
+            // right by 16 bits, then we will net a right shift of 7 bits.
+            // However, this won't work as intended. Since we clip the
+            // values to have a maximum value of 127, shifting it by 9 bits
+            // might occupy the signed bit, resulting in some positive
+            // values being interpreted as negative after the shift.
+
+            // There is a way, however, to get around this limitation. When
+            // loading the network, scale accumulator weights and biases by
+            // 2. To get the same pairwise multiplication result as before,
+            // we need to divide the product by 128 * 2 * 2 = 512, which
+            // amounts to a right shift of 9 bits. So now we only have to
+            // shift left by 7 bits, perform mulhi (shifts right by 16 bits)
+            // and net a 9 bit right shift. Since we scaled everything by
+            // two, the values are clipped at 127 * 2 = 254, which occupies
+            // 8 bits. Shifting it by 7 bits left will no longer occupy the
+            // signed bit, so we are safe.
+
+            // Note that on NEON processors, we shift left by 6 instead
+            // because the instruction "vqdmulhq_s16" also doubles the
+            // return value after the multiplication, adding an extra shift
+            // to the left by 1, so we compensate by shifting less before
+            // the multiplication.
+
+            constexpr int shift =
+    #if defined(USE_SSE2)
+              7;
+    #else
+              6;
+    #endif
+
+            for (IndexType j = 0; j < NumOutputChunks; ++j)
+            {
+                const vec_t sum0a =
+                  vec_slli_16(vec_max_16(vec_min_16(in0[j * 2 + 0], One), Zero), shift);
+                const vec_t sum0b =
+                  vec_slli_16(vec_max_16(vec_min_16(in0[j * 2 + 1], One), Zero), shift);
+                const vec_t sum1a = vec_min_16(in1[j * 2 + 0], One);
+                const vec_t sum1b = vec_min_16(in1[j * 2 + 1], One);
+
+                const vec_t pa = vec_mulhi_16(sum0a, sum1a);
+                const vec_t pb = vec_mulhi_16(sum0b, sum1b);
+
+                out[j] = vec_packus_16(pa, pb);
+            }
+
+#else
 
+            for (IndexType j = 0; j < HalfDimensions / 2; ++j)
+            {
+                BiasType sum0 = accumulation[static_cast<int>(perspectives[p])][j + 0];
+                BiasType sum1 =
+                  accumulation[static_cast<int>(perspectives[p])][j + HalfDimensions / 2];
+                sum0               = std::clamp<BiasType>(sum0, 0, 127 * 2);
+                sum1               = std::clamp<BiasType>(sum1, 0, 127 * 2);
+                output[offset + j] = static_cast<OutputType>(unsigned(sum0 * sum1) / 512);
+            }
+
+#endif
         }
-      }
 
-      accumulator.computed_accumulation = true;
-      accumulator.computed_score = false;
+        return psqt;
+    }  // end of function transform()
+
+    void hint_common_access(const Position&                           pos,
+                            AccumulatorCaches::Cache<HalfDimensions>* cache) const {
+        hint_common_access_for_perspective<WHITE>(pos, cache);
+        hint_common_access_for_perspective<BLACK>(pos, cache);
     }
 
-    // Calculate cumulative value using difference calculation
-    void UpdateAccumulator(const Position& pos) const {
-      const auto prev_accumulator = pos.state()->previous->accumulator;
-      auto& accumulator = pos.state()->accumulator;
-      IndexType i = 0;
-      Features::IndexList removed_indices[2], added_indices[2];
-      bool reset[2];
-      RawFeatures::AppendChangedIndices(pos, kRefreshTriggers[i],
-                                        removed_indices, added_indices, reset);
-      for (Color perspective : { WHITE, BLACK }) {
-
-  #if defined(USE_AVX2)
-        constexpr IndexType kNumChunks = kHalfDimensions / (kSimdWidth / 2);
-        auto accumulation = reinterpret_cast<__m256i*>(
-            &accumulator.accumulation[perspective][i][0]);
-
-  #elif defined(USE_SSE2)
-        constexpr IndexType kNumChunks = kHalfDimensions / (kSimdWidth / 2);
-        auto accumulation = reinterpret_cast<__m128i*>(
-            &accumulator.accumulation[perspective][i][0]);
-
-  #elif defined(USE_NEON)
-        constexpr IndexType kNumChunks = kHalfDimensions / (kSimdWidth / 2);
-        auto accumulation = reinterpret_cast<int16x8_t*>(
-            &accumulator.accumulation[perspective][i][0]);
-  #endif
-
-        if (reset[perspective]) {
-          std::memcpy(accumulator.accumulation[perspective][i], biases_,
-                      kHalfDimensions * sizeof(BiasType));
-        } else {
-          std::memcpy(accumulator.accumulation[perspective][i],
-                      prev_accumulator.accumulation[perspective][i],
-                      kHalfDimensions * sizeof(BiasType));
-          // Difference calculation for the deactivated features
-          for (const auto index : removed_indices[perspective]) {
-            const IndexType offset = kHalfDimensions * index;
-
-  #if defined(USE_AVX2)
-            auto column = reinterpret_cast<const __m256i*>(&weights_[offset]);
-            for (IndexType j = 0; j < kNumChunks; ++j) {
-              accumulation[j] = _mm256_sub_epi16(accumulation[j], column[j]);
-            }
+   private:
+    template<Color Perspective>
+    StateInfo* try_find_computed_accumulator(const Position& pos) const {
+        // Look for a usable accumulator of an earlier position. We keep track
+        // of the estimated gain in terms of features to be added/subtracted.
+        StateInfo* st   = pos.state();
+        int        gain = FeatureSet::refresh_cost(pos);
+        while (st->previous && !(st->*accPtr).computed[Perspective])
+        {
+            // This governs when a full feature refresh is needed and how many
+            // updates are better than just one full refresh.
+            if (FeatureSet::requires_refresh(st, Perspective)
+                || (gain -= FeatureSet::update_cost(st) + 1) < 0)
+                break;
+            st = st->previous;
+        }
+        return st;
+    }
 
-  #elif defined(USE_SSE2)
-            auto column = reinterpret_cast<const __m128i*>(&weights_[offset]);
-            for (IndexType j = 0; j < kNumChunks; ++j) {
-              accumulation[j] = _mm_sub_epi16(accumulation[j], column[j]);
+    // It computes the accumulator of the next position, or updates the
+    // current position's accumulator if CurrentOnly is true.
+    template<Color Perspective, bool CurrentOnly>
+    void update_accumulator_incremental(const Position& pos, StateInfo* computed) const {
+        assert((computed->*accPtr).computed[Perspective]);
+        assert(computed->next != nullptr);
+
+#ifdef VECTOR
+        // Gcc-10.2 unnecessarily spills AVX2 registers if this array
+        // is defined in the VECTOR code below, once in each branch.
+        vec_t      acc[NumRegs];
+        psqt_vec_t psqt[NumPsqtRegs];
+#endif
+
+        const Square ksq = pos.square<KING>(Perspective);
+
+        // The size must be enough to contain the largest possible update.
+        // That might depend on the feature set and generally relies on the
+        // feature set's update cost calculation to be correct and never allow
+        // updates with more added/removed features than MaxActiveDimensions.
+        FeatureSet::IndexList removed, added;
+
+        if constexpr (CurrentOnly)
+            for (StateInfo* st = pos.state(); st != computed; st = st->previous)
+                FeatureSet::append_changed_indices<Perspective>(ksq, st->dirtyPiece, removed,
+                                                                added);
+        else
+            FeatureSet::append_changed_indices<Perspective>(ksq, computed->next->dirtyPiece,
+                                                            removed, added);
+
+        StateInfo* next = CurrentOnly ? pos.state() : computed->next;
+        assert(!(next->*accPtr).computed[Perspective]);
+
+#ifdef VECTOR
+        if ((removed.size() == 1 || removed.size() == 2) && added.size() == 1)
+        {
+            auto accIn =
+              reinterpret_cast<const vec_t*>(&(computed->*accPtr).accumulation[Perspective][0]);
+            auto accOut = reinterpret_cast<vec_t*>(&(next->*accPtr).accumulation[Perspective][0]);
+
+            const IndexType offsetR0 = HalfDimensions * removed[0];
+            auto            columnR0 = reinterpret_cast<const vec_t*>(&weights[offsetR0]);
+            const IndexType offsetA  = HalfDimensions * added[0];
+            auto            columnA  = reinterpret_cast<const vec_t*>(&weights[offsetA]);
+
+            if (removed.size() == 1)
+            {
+                for (IndexType i = 0; i < HalfDimensions * sizeof(WeightType) / sizeof(vec_t); ++i)
+                    accOut[i] = vec_add_16(vec_sub_16(accIn[i], columnR0[i]), columnA[i]);
+            }
+            else
+            {
+                const IndexType offsetR1 = HalfDimensions * removed[1];
+                auto            columnR1 = reinterpret_cast<const vec_t*>(&weights[offsetR1]);
+
+                for (IndexType i = 0; i < HalfDimensions * sizeof(WeightType) / sizeof(vec_t); ++i)
+                    accOut[i] = vec_sub_16(vec_add_16(accIn[i], columnA[i]),
+                                           vec_add_16(columnR0[i], columnR1[i]));
             }
 
-  #elif defined(USE_NEON)
-            auto column = reinterpret_cast<const int16x8_t*>(&weights_[offset]);
-            for (IndexType j = 0; j < kNumChunks; ++j) {
-              accumulation[j] = vsubq_s16(accumulation[j], column[j]);
+            auto accPsqtIn = reinterpret_cast<const psqt_vec_t*>(
+              &(computed->*accPtr).psqtAccumulation[Perspective][0]);
+            auto accPsqtOut =
+              reinterpret_cast<psqt_vec_t*>(&(next->*accPtr).psqtAccumulation[Perspective][0]);
+
+            const IndexType offsetPsqtR0 = PSQTBuckets * removed[0];
+            auto columnPsqtR0 = reinterpret_cast<const psqt_vec_t*>(&psqtWeights[offsetPsqtR0]);
+            const IndexType offsetPsqtA = PSQTBuckets * added[0];
+            auto columnPsqtA = reinterpret_cast<const psqt_vec_t*>(&psqtWeights[offsetPsqtA]);
+
+            if (removed.size() == 1)
+            {
+                for (std::size_t i = 0;
+                     i < PSQTBuckets * sizeof(PSQTWeightType) / sizeof(psqt_vec_t); ++i)
+                    accPsqtOut[i] = vec_add_psqt_32(vec_sub_psqt_32(accPsqtIn[i], columnPsqtR0[i]),
+                                                    columnPsqtA[i]);
+            }
+            else
+            {
+                const IndexType offsetPsqtR1 = PSQTBuckets * removed[1];
+                auto columnPsqtR1 = reinterpret_cast<const psqt_vec_t*>(&psqtWeights[offsetPsqtR1]);
+
+                for (std::size_t i = 0;
+                     i < PSQTBuckets * sizeof(PSQTWeightType) / sizeof(psqt_vec_t); ++i)
+                    accPsqtOut[i] =
+                      vec_sub_psqt_32(vec_add_psqt_32(accPsqtIn[i], columnPsqtA[i]),
+                                      vec_add_psqt_32(columnPsqtR0[i], columnPsqtR1[i]));
+            }
+        }
+        else
+        {
+            for (IndexType i = 0; i < HalfDimensions / TileHeight; ++i)
+            {
+                // Load accumulator
+                auto accTileIn = reinterpret_cast<const vec_t*>(
+                  &(computed->*accPtr).accumulation[Perspective][i * TileHeight]);
+                for (IndexType j = 0; j < NumRegs; ++j)
+                    acc[j] = vec_load(&accTileIn[j]);
+
+                // Difference calculation for the deactivated features
+                for (const auto index : removed)
+                {
+                    const IndexType offset = HalfDimensions * index + i * TileHeight;
+                    auto            column = reinterpret_cast<const vec_t*>(&weights[offset]);
+                    for (IndexType j = 0; j < NumRegs; ++j)
+                        acc[j] = vec_sub_16(acc[j], column[j]);
+                }
+
+                // Difference calculation for the activated features
+                for (const auto index : added)
+                {
+                    const IndexType offset = HalfDimensions * index + i * TileHeight;
+                    auto            column = reinterpret_cast<const vec_t*>(&weights[offset]);
+                    for (IndexType j = 0; j < NumRegs; ++j)
+                        acc[j] = vec_add_16(acc[j], column[j]);
+                }
+
+                // Store accumulator
+                auto accTileOut = reinterpret_cast<vec_t*>(
+                  &(next->*accPtr).accumulation[Perspective][i * TileHeight]);
+                for (IndexType j = 0; j < NumRegs; ++j)
+                    vec_store(&accTileOut[j], acc[j]);
             }
 
-  #else
-            for (IndexType j = 0; j < kHalfDimensions; ++j) {
-              accumulator.accumulation[perspective][i][j] -=
-                  weights_[offset + j];
+            for (IndexType i = 0; i < PSQTBuckets / PsqtTileHeight; ++i)
+            {
+                // Load accumulator
+                auto accTilePsqtIn = reinterpret_cast<const psqt_vec_t*>(
+                  &(computed->*accPtr).psqtAccumulation[Perspective][i * PsqtTileHeight]);
+                for (std::size_t j = 0; j < NumPsqtRegs; ++j)
+                    psqt[j] = vec_load_psqt(&accTilePsqtIn[j]);
+
+                // Difference calculation for the deactivated features
+                for (const auto index : removed)
+                {
+                    const IndexType offset = PSQTBuckets * index + i * PsqtTileHeight;
+                    auto columnPsqt = reinterpret_cast<const psqt_vec_t*>(&psqtWeights[offset]);
+                    for (std::size_t j = 0; j < NumPsqtRegs; ++j)
+                        psqt[j] = vec_sub_psqt_32(psqt[j], columnPsqt[j]);
+                }
+
+                // Difference calculation for the activated features
+                for (const auto index : added)
+                {
+                    const IndexType offset = PSQTBuckets * index + i * PsqtTileHeight;
+                    auto columnPsqt = reinterpret_cast<const psqt_vec_t*>(&psqtWeights[offset]);
+                    for (std::size_t j = 0; j < NumPsqtRegs; ++j)
+                        psqt[j] = vec_add_psqt_32(psqt[j], columnPsqt[j]);
+                }
+
+                // Store accumulator
+                auto accTilePsqtOut = reinterpret_cast<psqt_vec_t*>(
+                  &(next->*accPtr).psqtAccumulation[Perspective][i * PsqtTileHeight]);
+                for (std::size_t j = 0; j < NumPsqtRegs; ++j)
+                    vec_store_psqt(&accTilePsqtOut[j], psqt[j]);
             }
-  #endif
+        }
+#else
+        std::memcpy((next->*accPtr).accumulation[Perspective],
+                    (computed->*accPtr).accumulation[Perspective],
+                    HalfDimensions * sizeof(BiasType));
+        std::memcpy((next->*accPtr).psqtAccumulation[Perspective],
+                    (computed->*accPtr).psqtAccumulation[Perspective],
+                    PSQTBuckets * sizeof(PSQTWeightType));
+
+        // Difference calculation for the deactivated features
+        for (const auto index : removed)
+        {
+            const IndexType offset = HalfDimensions * index;
+            for (IndexType i = 0; i < HalfDimensions; ++i)
+                (next->*accPtr).accumulation[Perspective][i] -= weights[offset + i];
+
+            for (std::size_t i = 0; i < PSQTBuckets; ++i)
+                (next->*accPtr).psqtAccumulation[Perspective][i] -=
+                  psqtWeights[index * PSQTBuckets + i];
+        }
+
+        // Difference calculation for the activated features
+        for (const auto index : added)
+        {
+            const IndexType offset = HalfDimensions * index;
+            for (IndexType i = 0; i < HalfDimensions; ++i)
+                (next->*accPtr).accumulation[Perspective][i] += weights[offset + i];
 
-          }
+            for (std::size_t i = 0; i < PSQTBuckets; ++i)
+                (next->*accPtr).psqtAccumulation[Perspective][i] +=
+                  psqtWeights[index * PSQTBuckets + i];
         }
-        { // Difference calculation for the activated features
-          for (const auto index : added_indices[perspective]) {
-            const IndexType offset = kHalfDimensions * index;
-
-  #if defined(USE_AVX2)
-            auto column = reinterpret_cast<const __m256i*>(&weights_[offset]);
-            for (IndexType j = 0; j < kNumChunks; ++j) {
-              accumulation[j] = _mm256_add_epi16(accumulation[j], column[j]);
-            }
+#endif
 
-  #elif defined(USE_SSE2)
-            auto column = reinterpret_cast<const __m128i*>(&weights_[offset]);
-            for (IndexType j = 0; j < kNumChunks; ++j) {
-              accumulation[j] = _mm_add_epi16(accumulation[j], column[j]);
+        (next->*accPtr).computed[Perspective] = true;
+
+        if (!CurrentOnly && next != pos.state())
+            update_accumulator_incremental<Perspective, false>(pos, next);
+    }
+
+    template<Color Perspective>
+    void update_accumulator_refresh_cache(const Position&                           pos,
+                                          AccumulatorCaches::Cache<HalfDimensions>* cache) const {
+        assert(cache != nullptr);
+
+        Square                ksq   = pos.square<KING>(Perspective);
+        auto&                 entry = (*cache)[ksq][Perspective];
+        FeatureSet::IndexList removed, added;
+
+        for (Color c : {WHITE, BLACK})
+        {
+            for (PieceType pt = PAWN; pt <= KING; ++pt)
+            {
+                const Piece    piece    = make_piece(c, pt);
+                const Bitboard oldBB    = entry.byColorBB[c] & entry.byTypeBB[pt];
+                const Bitboard newBB    = pos.pieces(c, pt);
+                Bitboard       toRemove = oldBB & ~newBB;
+                Bitboard       toAdd    = newBB & ~oldBB;
+
+                while (toRemove)
+                {
+                    Square sq = pop_lsb(toRemove);
+                    removed.push_back(FeatureSet::make_index<Perspective>(sq, piece, ksq));
+                }
+                while (toAdd)
+                {
+                    Square sq = pop_lsb(toAdd);
+                    added.push_back(FeatureSet::make_index<Perspective>(sq, piece, ksq));
+                }
             }
+        }
 
-  #elif defined(USE_NEON)
-            auto column = reinterpret_cast<const int16x8_t*>(&weights_[offset]);
-            for (IndexType j = 0; j < kNumChunks; ++j) {
-              accumulation[j] = vaddq_s16(accumulation[j], column[j]);
+        auto& accumulator                 = pos.state()->*accPtr;
+        accumulator.computed[Perspective] = true;
+
+#ifdef VECTOR
+        vec_t      acc[NumRegs];
+        psqt_vec_t psqt[NumPsqtRegs];
+
+        for (IndexType j = 0; j < HalfDimensions / TileHeight; ++j)
+        {
+            auto accTile =
+              reinterpret_cast<vec_t*>(&accumulator.accumulation[Perspective][j * TileHeight]);
+            auto entryTile = reinterpret_cast<vec_t*>(&entry.accumulation[j * TileHeight]);
+
+            for (IndexType k = 0; k < NumRegs; ++k)
+                acc[k] = entryTile[k];
+
+            int i = 0;
+            for (; i < int(std::min(removed.size(), added.size())); ++i)
+            {
+                IndexType       indexR  = removed[i];
+                const IndexType offsetR = HalfDimensions * indexR + j * TileHeight;
+                auto            columnR = reinterpret_cast<const vec_t*>(&weights[offsetR]);
+                IndexType       indexA  = added[i];
+                const IndexType offsetA = HalfDimensions * indexA + j * TileHeight;
+                auto            columnA = reinterpret_cast<const vec_t*>(&weights[offsetA]);
+
+                for (unsigned k = 0; k < NumRegs; ++k)
+                    acc[k] = vec_add_16(acc[k], vec_sub_16(columnA[k], columnR[k]));
+            }
+            for (; i < int(removed.size()); ++i)
+            {
+                IndexType       index  = removed[i];
+                const IndexType offset = HalfDimensions * index + j * TileHeight;
+                auto            column = reinterpret_cast<const vec_t*>(&weights[offset]);
+
+                for (unsigned k = 0; k < NumRegs; ++k)
+                    acc[k] = vec_sub_16(acc[k], column[k]);
+            }
+            for (; i < int(added.size()); ++i)
+            {
+                IndexType       index  = added[i];
+                const IndexType offset = HalfDimensions * index + j * TileHeight;
+                auto            column = reinterpret_cast<const vec_t*>(&weights[offset]);
+
+                for (unsigned k = 0; k < NumRegs; ++k)
+                    acc[k] = vec_add_16(acc[k], column[k]);
             }
 
-  #else
-            for (IndexType j = 0; j < kHalfDimensions; ++j) {
-              accumulator.accumulation[perspective][i][j] +=
-                  weights_[offset + j];
+            for (IndexType k = 0; k < NumRegs; k++)
+                vec_store(&entryTile[k], acc[k]);
+            for (IndexType k = 0; k < NumRegs; k++)
+                vec_store(&accTile[k], acc[k]);
+        }
+
+        for (IndexType j = 0; j < PSQTBuckets / PsqtTileHeight; ++j)
+        {
+            auto accTilePsqt = reinterpret_cast<psqt_vec_t*>(
+              &accumulator.psqtAccumulation[Perspective][j * PsqtTileHeight]);
+            auto entryTilePsqt =
+              reinterpret_cast<psqt_vec_t*>(&entry.psqtAccumulation[j * PsqtTileHeight]);
+
+            for (std::size_t k = 0; k < NumPsqtRegs; ++k)
+                psqt[k] = entryTilePsqt[k];
+
+            for (int i = 0; i < int(removed.size()); ++i)
+            {
+                IndexType       index  = removed[i];
+                const IndexType offset = PSQTBuckets * index + j * PsqtTileHeight;
+                auto columnPsqt        = reinterpret_cast<const psqt_vec_t*>(&psqtWeights[offset]);
+
+                for (std::size_t k = 0; k < NumPsqtRegs; ++k)
+                    psqt[k] = vec_sub_psqt_32(psqt[k], columnPsqt[k]);
+            }
+            for (int i = 0; i < int(added.size()); ++i)
+            {
+                IndexType       index  = added[i];
+                const IndexType offset = PSQTBuckets * index + j * PsqtTileHeight;
+                auto columnPsqt        = reinterpret_cast<const psqt_vec_t*>(&psqtWeights[offset]);
+
+                for (std::size_t k = 0; k < NumPsqtRegs; ++k)
+                    psqt[k] = vec_add_psqt_32(psqt[k], columnPsqt[k]);
             }
-  #endif
 
-          }
+            for (std::size_t k = 0; k < NumPsqtRegs; ++k)
+                vec_store_psqt(&entryTilePsqt[k], psqt[k]);
+            for (std::size_t k = 0; k < NumPsqtRegs; ++k)
+                vec_store_psqt(&accTilePsqt[k], psqt[k]);
+        }
+
+#else
+
+        for (const auto index : removed)
+        {
+            const IndexType offset = HalfDimensions * index;
+            for (IndexType j = 0; j < HalfDimensions; ++j)
+                entry.accumulation[j] -= weights[offset + j];
+
+            for (std::size_t k = 0; k < PSQTBuckets; ++k)
+                entry.psqtAccumulation[k] -= psqtWeights[index * PSQTBuckets + k];
+        }
+        for (const auto index : added)
+        {
+            const IndexType offset = HalfDimensions * index;
+            for (IndexType j = 0; j < HalfDimensions; ++j)
+                entry.accumulation[j] += weights[offset + j];
+
+            for (std::size_t k = 0; k < PSQTBuckets; ++k)
+                entry.psqtAccumulation[k] += psqtWeights[index * PSQTBuckets + k];
         }
-      }
 
-      accumulator.computed_accumulation = true;
-      accumulator.computed_score = false;
+        // The accumulator of the refresh entry has been updated.
+        // Now copy its content to the actual accumulator we were refreshing.
+
+        std::memcpy(accumulator.accumulation[Perspective], entry.accumulation,
+                    sizeof(BiasType) * HalfDimensions);
+
+        std::memcpy(accumulator.psqtAccumulation[Perspective], entry.psqtAccumulation,
+                    sizeof(int32_t) * PSQTBuckets);
+#endif
+
+        for (Color c : {WHITE, BLACK})
+            entry.byColorBB[c] = pos.pieces(c);
+
+        for (PieceType pt = PAWN; pt <= KING; ++pt)
+            entry.byTypeBB[pt] = pos.pieces(pt);
+    }
+
+    template<Color Perspective>
+    void hint_common_access_for_perspective(const Position&                           pos,
+                                            AccumulatorCaches::Cache<HalfDimensions>* cache) const {
+
+        // Works like update_accumulator, but performs less work.
+        // Updates ONLY the accumulator for pos.
+
+        // Look for a usable accumulator of an earlier position. We keep track
+        // of the estimated gain in terms of features to be added/subtracted.
+        // Fast early exit.
+        if ((pos.state()->*accPtr).computed[Perspective])
+            return;
+
+        StateInfo* oldest = try_find_computed_accumulator<Perspective>(pos);
+
+        if ((oldest->*accPtr).computed[Perspective] && oldest != pos.state())
+            update_accumulator_incremental<Perspective, true>(pos, oldest);
+        else
+            update_accumulator_refresh_cache<Perspective>(pos, cache);
+    }
+
+    template<Color Perspective>
+    void update_accumulator(const Position&                           pos,
+                            AccumulatorCaches::Cache<HalfDimensions>* cache) const {
+
+        StateInfo* oldest = try_find_computed_accumulator<Perspective>(pos);
+
+        if ((oldest->*accPtr).computed[Perspective] && oldest != pos.state())
+            // Start from the oldest computed accumulator, update all the
+            // accumulators up to the current position.
+            update_accumulator_incremental<Perspective, false>(pos, oldest);
+        else
+            update_accumulator_refresh_cache<Perspective>(pos, cache);
     }
 
-    using BiasType = std::int16_t;
-    using WeightType = std::int16_t;
+    template<IndexType Size>
+    friend struct AccumulatorCaches::Cache;
 
-    alignas(kCacheLineSize) BiasType biases_[kHalfDimensions];
-    alignas(kCacheLineSize)
-        WeightType weights_[kHalfDimensions * kInputDimensions];
-  };
+    alignas(CacheLineSize) BiasType biases[HalfDimensions];
+    alignas(CacheLineSize) WeightType weights[HalfDimensions * InputDimensions];
+    alignas(CacheLineSize) PSQTWeightType psqtWeights[InputDimensions * PSQTBuckets];
+};
 
-}  // namespace Eval::NNUE
+}  // namespace Stockfish::Eval::NNUE
 
-#endif // #ifndef NNUE_FEATURE_TRANSFORMER_H_INCLUDED
+#endif  // #ifndef NNUE_FEATURE_TRANSFORMER_H_INCLUDED