Update nnue architecture to SFNNv16 and net nn-89cb98a217f7.nnue

Failed STC (https://tests.stockfishchess.org/tests/view/6a4f36355529b8472df7ff7e):
LLR: -2.94 (-2.94,2.94) <0.00,2.00>
Total: 144768 W: 38003 L: 38051 D: 68714
Ptnml(0-2): 521, 17154, 37050, 17170, 489

Passed LTC (https://tests.stockfishchess.org/tests/view/6a501dad5529b8472df80103):
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 189888 W: 49613 L: 48984 D: 91291
Ptnml(0-2): 122, 20406, 53256, 21041, 119

Passed VLTC (https://tests.stockfishchess.org/tests/view/6a52892c5529b8472df80481):
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 46124 W: 12156 L: 11865 D: 22103
Ptnml(0-2): 12, 4523, 13696, 4824, 7

Passed VVLTC (https://tests.stockfishchess.org/tests/view/6a566a285529b8472df80b84):
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 44698 W: 11805 L: 11507 D: 21386
Ptnml(0-2): 9, 3819, 14395, 4117, 9

This PR adds pawn pair features, a new set of features that is indexed by pairs of pawns occupying the same or adjacent files (hence "3-wide"). Because these are a superset of pawn–pawn interactions in threat inputs (including the recently added pawn-pusher inputs), those are removed. HalfKA features remain unchanged.

Pawn-pair features were invented by Jonathan for Pawnocchio, based on his observation that in a net trained on *all* pairs of pawns, the most important pawn pairs were those differing by at most one file.

sscg13 made the necessary changes to the trainer (https://github.com/official-stockfish/nnue-pytorch/pull/502) and initial changes to inference. The slowdown was originally far too large (some 10%); following major optimizations from Jonathan and a bit from me, the slowdown is small enough for a comfortable LTC pass; on my machine I get a 3.5% slowdown overall. I expect there are further "easy" speedups in the new code, so this gap should narrow a bit.

Nettest PR: https://github.com/vondele/nettest/pull/359

closes https://github.com/official-stockfish/Stockfish/pull/6982

Bench: 2718396

Co-Authored-By: anematode <timothy.herchen@gmail.com>
Co-Authored-By: Jonathan Hallström <lmj.hallstrom@gmail.com>

src/Makefile

@@ -80,14 +80,14 @@ SRCS = attacks.cpp benchmark.cpp bitboard.cpp evaluate.cpp main.cpp \
 	misc.cpp movegen.cpp movepick.cpp position.cpp \
 	search.cpp thread.cpp timeman.cpp tt.cpp uci.cpp ucioption.cpp tune.cpp syzygy/tbprobe.cpp \
 	nnue/nnue_accumulator.cpp nnue/nnue_misc.cpp nnue/network.cpp \
-	nnue/features/half_ka_v2_hm.cpp nnue/features/full_threats.cpp \
+	nnue/features/half_ka_v2_hm.cpp nnue/features/full_threats.cpp nnue/features/pp_3wide.cpp \
 	engine.cpp score.cpp memory.cpp
 
 OTHER_SRCS = universal/entry_x86.cpp universal/entry_arm64.cpp universal/entry_riscv64.cpp universal/nnue_embed.cpp
 
 HEADERS = attacks.h benchmark.h bitboard.h evaluate.h misc.h movegen.h movepick.h history.h \
 		nnue/nnue_misc.h nnue/features/half_ka_v2_hm.h nnue/features/full_threats.h \
-		nnue/layers/affine_transform.h nnue/layers/affine_transform_sparse_input.h \
+		nnue/features/pp_3wide.h nnue/layers/affine_transform.h nnue/layers/affine_transform_sparse_input.h \
 		nnue/layers/clipped_relu.h nnue/layers/sqr_clipped_relu.h nnue/nnue_accumulator.h \
 		nnue/nnue_architecture.h nnue/nnue_common.h nnue/nnue_feature_transformer.h nnue/simd.h \
 		nnue/nnz_helper.h position.h search.h syzygy/tbprobe.h thread.h thread_native.h timeman.h \

src/bitboard.h

@@ -20,6 +20,7 @@
 #define BITBOARD_H_INCLUDED
 
 #include <algorithm>
+#include <array>
 #include <cassert>
 #include <string>
 #include <type_traits>
@@ -127,8 +128,23 @@ constexpr Bitboard pawn_single_push_bb(Color c, Bitboard b) {
     return c == WHITE ? shift<NORTH>(b) : shift<SOUTH>(b);
 }
 
-constexpr int edge_distance(File f) { return std::min(f, File(FILE_H - f)); }
+inline constexpr auto PawnPairBB = []() {
+    std::array<Bitboard, SQUARE_NB> result{};
+    for (Square s = SQ_A1; s <= SQ_H8; ++s)
+    {
+        Bitboard file  = file_bb(s);
+        Bitboard files = file | shift<EAST>(file) | shift<WEST>(file);
+        result[s]      = files & ~(Rank1BB | Rank8BB) & ~square_bb(s);
+    }
+    return result;
+}();
 
+// Returns the squares that can host a pawn forming a "pawn pair" with a pawn
+// on s: own file plus adjacent files, restricted to ranks 2-7, excluding s.
+// The geometry is color-independent.
+constexpr Bitboard pawn_pair_bb(Square s) { return PawnPairBB[s]; }
+
+constexpr int edge_distance(File f) { return std::min(f, File(FILE_H - f)); }
 
 template<typename T>
 constexpr int constexpr_popcount(T v) {

src/evaluate.h

@@ -33,7 +33,7 @@ namespace Eval {
 // for the build process (profile-build and fishtest) to work. Do not change the
 // name of the macro or the location where this macro is defined, as it is used
 // in the Makefile/Fishtest.
-#define EvalFileDefaultName "nn-0ee0657fb25e.nnue"
+#define EvalFileDefaultName "nn-89cb98a217f7.nnue"
 
 namespace NNUE {
 class Network;

src/nnue/features/full_threats.cpp

@@ -21,7 +21,6 @@
 #include "full_threats.h"
 
 #include <array>
-#include <cassert>
 #include <cstdint>
 #include <initializer_list>
 #include <utility>
@@ -73,7 +72,7 @@ constexpr auto make_piece_indices_piece() {
 
     for (Square from = SQ_A1; from <= SQ_H8; ++from)
     {
-        Bitboard attacks = Attacks::PawnPushOrAttacks[C][from];
+        Bitboard attacks = Attacks::PseudoAttacks[C][from];
 
         for (Square to = SQ_A1; to <= SQ_H8; ++to)
         {
@@ -136,8 +135,8 @@ constexpr auto init_threat_offsets() {
 
             else if (from >= SQ_A2 && from <= SQ_H7)
             {
-                Bitboard attacks = (pieceIdx < 8) ? Attacks::PawnPushOrAttacks[WHITE][from]
+                Bitboard attacks = (pieceIdx < 8) ? Attacks::PseudoAttacks[WHITE][from]
-                                                  : Attacks::PawnPushOrAttacks[BLACK][from];
+                                                  : Attacks::PseudoAttacks[BLACK][from];
                 cumulativePieceOffset += constexpr_popcount(attacks);
             }
         }
@@ -208,11 +207,9 @@ inline sf_always_inline IndexType FullThreats::make_index(
 // Get a list of indices for active features in ascending order
 
 void FullThreats::append_active_indices(Color perspective, const Position& pos, IndexList& active) {
-    const Square   ksq      = pos.square<KING>(perspective);
+    const Square   ksq                = pos.square<KING>(perspective);
-    const Bitboard occupied = pos.pieces();
+    const Bitboard occupied           = pos.pieces();
-    const Bitboard pawns    = pos.pieces(PAWN);
+    const Bitboard pawnTargets        = pos.pieces(KNIGHT, ROOK);
-
-    const Bitboard pawnTargets        = pos.pieces(PAWN, KNIGHT, ROOK);
     const Bitboard minorSliderTargets = pos.pieces(PAWN, KNIGHT, BISHOP, ROOK);
     const Bitboard queenTargets       = pos.pieces(PAWN, KNIGHT, BISHOP, ROOK, QUEEN);
 
@@ -221,18 +218,14 @@ void FullThreats::append_active_indices(Color perspective, const Position& pos,
         const Color c = Color(perspective ^ color);
 
         {
-            const Piece    attacker = make_piece(c, PAWN);
+            const Piece    attacker             = make_piece(c, PAWN);
-            const Bitboard cPawns   = pos.pieces(c, PAWN);
+            const Bitboard cPawns               = pos.pieces(c, PAWN);
-            // Set of pawns which are prevented from movement by a pawn in front of them
+            auto           process_pawn_attacks = [&](Bitboard attacks, Direction attkDir) {
-            const Bitboard pushers = pawn_single_push_bb(~c, pawns) & cPawns;
-
-            auto process_pawn_attacks = [&](Bitboard attacks, Direction attkDir) {
                 while (attacks)
                 {
-                    Square to       = pop_lsb(attacks);
+                    Square    to       = pop_lsb(attacks);
-                    Square from     = to - attkDir;
+                    Square    from     = to - attkDir;
-                    Piece  attacked = pos.piece_on(to);
+                    Piece     attacked = pos.piece_on(to);
-                    assert(file_of(from) != file_of(to) || type_of(attacked) == PAWN);
                     IndexType index = make_index(perspective, attacker, from, to, attacked, ksq);
                     active.push_back_if_lt(index, Dimensions);
                 }
@@ -242,13 +235,11 @@ void FullThreats::append_active_indices(Color perspective, const Position& pos,
             {
                 process_pawn_attacks(shift<NORTH_EAST>(cPawns) & pawnTargets, NORTH_EAST);
                 process_pawn_attacks(shift<NORTH_WEST>(cPawns) & pawnTargets, NORTH_WEST);
-                process_pawn_attacks(shift<NORTH>(pushers), NORTH);
             }
             else
             {
                 process_pawn_attacks(shift<SOUTH_WEST>(cPawns) & pawnTargets, SOUTH_WEST);
                 process_pawn_attacks(shift<SOUTH_EAST>(cPawns) & pawnTargets, SOUTH_EAST);
-                process_pawn_attacks(shift<SOUTH>(pushers), SOUTH);
             }
         }
 

src/nnue/features/full_threats.h

@@ -29,16 +29,18 @@ class Position;
 
 namespace Stockfish::Eval::NNUE::Features {
 
-static constexpr int numValidTargets[PIECE_NB] = {0, 6, 10, 8, 8, 10, 0, 0,
+// Pawn diagonal threats only target knights and rooks (pawn-pawn relationships
-                                                  0, 6, 10, 8, 8, 10, 0, 0};
+// are handled by the PP_3Wide feature set), so pawns have 4 valid targets.
+static constexpr int numValidTargets[PIECE_NB] = {0, 4, 10, 8, 8, 10, 0, 0,
+                                                  0, 4, 10, 8, 8, 10, 0, 0};
 
 class FullThreats {
    public:
     // Hash value embedded in the evaluation file
-    static constexpr u32 HashValue = 0x8f234cb8u;
+    static constexpr u32 HashValue = 0x2e6b9d04u;
 
     // Number of feature dimensions
-    static constexpr IndexType Dimensions = 60720;
+    static constexpr IndexType Dimensions = 59808;
 
     // clang-format off
     // Orient a square according to perspective (rotates by 180 for black)
@@ -54,7 +56,7 @@ class FullThreats {
     };
 
     static constexpr int map[PIECE_TYPE_NB-2][PIECE_TYPE_NB-2] = {
-      { 0,  1, -1,  2, -1, -1},
+      {-1,  0, -1,  1, -1, -1},
       { 0,  1,  2,  3,  4, -1},
       { 0,  1,  2,  3, -1, -1},
       { 0,  1,  2,  3, -1, -1},
@@ -64,9 +66,8 @@ class FullThreats {
     // clang-format on
 
     // Maximum number of simultaneously active features.
-    static constexpr IndexType MaxActiveDimensions = 128;
+    using IndexList = ValueList<u16, 256>;
-    using IndexList                                = ValueList<IndexType, MaxActiveDimensions>;
+    using DiffType  = DirtyThreats;
-    using DiffType                                 = DirtyThreats;
 
     static IndexType
     make_index(Color perspective, Piece attkr, Square from, Square to, Piece attkd, Square ksq);

src/nnue/features/pp_3wide.cpp

@@ -0,0 +1,171 @@
+/*
+  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
+  Copyright (C) 2004-2026 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
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  Stockfish is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include "pp_3wide.h"
+
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+
+#include "full_threats.h"
+#include "../../bitboard.h"
+#include "../../misc.h"
+#include "../../position.h"
+#include "../../types.h"
+#include "../nnue_common.h"
+
+namespace Stockfish::Eval::NNUE::Features {
+
+constexpr IndexType make_pawn_id(Color color, Square square) {
+    assert(square >= SQ_A2 && square <= SQ_H7);
+    return 48 * int(color) + square - SQ_A2;
+}
+
+#ifdef USE_AVX512ICL
+static inline __m256i pp_idx_epi16(__m256i a, __m256i b) {
+    const __m256i hi   = _mm256_max_epu16(a, b);
+    const __m256i lo   = _mm256_min_epu16(a, b);
+    const __m256i prod = _mm256_mullo_epi16(hi, _mm256_sub_epi16(hi, _mm256_set1_epi16(1)));
+    return _mm256_add_epi16(_mm256_add_epi16(_mm256_srli_epi16(prod, 1), lo),
+                            _mm256_set1_epi16(i16(PP_3Wide::IndexBase)));
+}
+#endif
+
+inline sf_always_inline IndexType PP_3Wide::make_index(
+  Color perspective, Color color, Square from, Square to, Color pairedColor, Square ksq) {
+    const i8 orientation   = FullThreats::OrientTBL[ksq] ^ (56 * perspective);
+    unsigned from_oriented = u8(from) ^ orientation;
+    unsigned to_oriented   = u8(to) ^ orientation;
+
+    Color color_oriented       = Color(color ^ perspective);
+    Color pairedColor_oriented = Color(pairedColor ^ perspective);
+
+    assert(from_oriented >= SQ_A2 && from_oriented <= SQ_H7);
+    assert(to_oriented >= SQ_A2 && to_oriented <= SQ_H7);
+
+    const IndexType idA = make_pawn_id(color_oriented, Square(from_oriented));
+    const IndexType idB = make_pawn_id(pairedColor_oriented, Square(to_oriented));
+    const IndexType hi  = std::max(idA, idB);
+    const IndexType lo  = std::min(idA, idB);
+
+    return hi * (hi - 1) / 2 + lo + IndexBase;
+}
+
+void PP_3Wide::append_active_indices(Color perspective, const Position& pos, IndexList& active) {
+    const Square   ksq   = pos.square<KING>(perspective);
+    const Bitboard white = pos.pieces(WHITE, PAWN);
+    const Bitboard black = pos.pieces(BLACK, PAWN);
+
+    Bitboard bb = white;
+    while (bb)
+    {
+        Square         from = pop_lsb(bb);
+        const Bitboard band = pawn_pair_bb(from);
+        for (Bitboard ww = band & bb; ww;)
+            active.push_back(make_index(perspective, WHITE, from, pop_lsb(ww), WHITE, ksq));
+        for (Bitboard wb = band & black; wb;)
+            active.push_back(make_index(perspective, WHITE, from, pop_lsb(wb), BLACK, ksq));
+    }
+
+    bb = black;
+    while (bb)
+    {
+        Square         from = pop_lsb(bb);
+        const Bitboard band = pawn_pair_bb(from);
+        for (Bitboard bbk = band & bb; bbk;)
+            active.push_back(make_index(perspective, BLACK, from, pop_lsb(bbk), BLACK, ksq));
+    }
+}
+
+void PP_3Wide::append_changed_indices(Color                                    perspective,
+                                      Square                                   ksq,
+                                      const DiffType&                          diff,
+                                      IndexList&                               removed,
+                                      IndexList&                               added,
+                                      [[maybe_unused]] const ThreatWeightType* prefetchBase,
+                                      [[maybe_unused]] IndexType               prefetchStride) {
+
+    const Bitboard whiteBefore = diff.before[WHITE];
+    const Bitboard blackBefore = diff.before[BLACK];
+    const Bitboard whiteAfter  = diff.after[WHITE];
+    const Bitboard blackAfter  = diff.after[BLACK];
+
+    if (whiteBefore == whiteAfter && blackBefore == blackAfter)
+        return;
+
+#ifdef USE_AVX512ICL
+    const u8      orientation = u8(FullThreats::OrientTBL[ksq]) ^ u8(56 * perspective);
+    const __m512i iota        = AllSquares;
+    const __m512i adjusted =
+      _mm512_sub_epi8(_mm512_xor_si512(iota, _mm512_set1_epi8(orientation)), _mm512_set1_epi8(8));
+
+    auto generate = [&](Bitboard updatedW, Bitboard updatedB, Bitboard pawnsW, Bitboard pawnsB,
+                        IndexList& out) {
+        const Bitboard friendly = perspective == WHITE ? pawnsW : pawnsB;
+        const Bitboard enemy    = perspective == WHITE ? pawnsB : pawnsW;
+        const __m512i  ids      = _mm512_mask_blend_epi8(
+          friendly, _mm512_add_epi8(adjusted, _mm512_set1_epi8(48)), adjusted);
+
+        const Bitboard unchanged = (pawnsW | pawnsB) & ~(updatedW | updatedB);
+        for (Bitboard u = updatedW | updatedB; u;)
+        {
+            const Square   a        = pop_lsb(u);
+            const Bitboard partners = pawn_pair_bb(a) & (unchanged | u);
+            const int      n        = popcount(partners);
+            if (!n)
+                continue;
+
+            const u16     colorOff = (enemy & a) ? 48 : 0;
+            const u16     aId      = u16(((u8(a) ^ orientation) - 8) + colorOff);
+            const __m256i pids     = _mm256_cvtepu8_epi16(
+              _mm512_castsi512_si128(_mm512_maskz_compress_epi8(partners, ids)));
+            const __m256i feats = pp_idx_epi16(_mm256_set1_epi16(aId), pids);
+
+            u16* w = out.make_space(n);
+            _mm256_storeu_epi16(w, feats);
+        }
+    };
+#else
+    auto generate = [&](Bitboard updatedW, Bitboard updatedB, Bitboard pawnsW, Bitboard pawnsB,
+                        IndexList& out) {
+        auto push = [&](IndexType index) {
+            if (prefetchBase)
+                prefetch<PrefetchRw::READ, PrefetchLoc::LOW>(reinterpret_cast<const void*>(
+                  reinterpret_cast<uintptr_t>(prefetchBase) + index * prefetchStride));
+            out.push_back(index);
+        };
+        const Bitboard unchanged = (pawnsW | pawnsB) & ~(updatedW | updatedB);
+        for (Bitboard u = updatedW | updatedB; u;)
+        {
+            const Square   a    = pop_lsb(u);
+            const Bitboard mask = pawn_pair_bb(a) & (unchanged | u);
+            const Color    aCol = (pawnsB & a) ? BLACK : WHITE;
+            for (Bitboard pb = pawnsB & mask; pb;)
+                push(make_index(perspective, aCol, a, pop_lsb(pb), BLACK, ksq));
+            for (Bitboard pw = pawnsW & mask; pw;)
+                push(make_index(perspective, aCol, a, pop_lsb(pw), WHITE, ksq));
+        }
+    };
+#endif
+
+    generate(whiteAfter & ~whiteBefore, blackAfter & ~blackBefore, whiteAfter, blackAfter, added);
+    generate(whiteBefore & ~whiteAfter, blackBefore & ~blackAfter, whiteBefore, blackBefore,
+             removed);
+}
+
+}  // namespace Stockfish::Eval::NNUE::Features

src/nnue/features/pp_3wide.h

@@ -0,0 +1,61 @@
+/*
+  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
+  Copyright (C) 2004-2026 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
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  Stockfish is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef NNUE_FEATURES_PP_3WIDE_INCLUDED
+#define NNUE_FEATURES_PP_3WIDE_INCLUDED
+
+#include "../../misc.h"
+#include "../../types.h"
+#include "../nnue_common.h"
+
+namespace Stockfish {
+class Position;
+}
+
+namespace Stockfish::Eval::NNUE::Features {
+
+class PP_3Wide {
+   public:
+    static constexpr u32 HashValue = 0x86f2b1ddu;
+
+    static constexpr IndexType PawnIds    = COLOR_NB * 48;
+    static constexpr IndexType Dimensions = PawnIds * (PawnIds - 1) / 2;
+
+    // Pawn pair feature indices are concatenated to threats, so this must equal ThreatFeatureSet::Dimensions;
+    // see nnue_feature_transformer.h
+    static constexpr IndexType IndexBase = 59808;
+    using IndexList                      = ValueList<u16, 256>;
+    using DiffType                       = DirtyPawnPairs;
+
+    static IndexType make_index(
+      Color perspective, Color color, Square from, Square to, Color pairedColor, Square ksq);
+
+    static void append_active_indices(Color perspective, const Position& pos, IndexList& active);
+
+    static void append_changed_indices(Color                   perspective,
+                                       Square                  ksq,
+                                       const DiffType&         diff,
+                                       IndexList&              removed,
+                                       IndexList&              added,
+                                       const ThreatWeightType* prefetchBase   = nullptr,
+                                       IndexType               prefetchStride = 0);
+};
+
+}  // namespace Stockfish::Eval::NNUE::Features
+
+#endif  // #ifndef NNUE_FEATURES_PP_3WIDE_INCLUDED

src/nnue/nnue_accumulator.cpp

@@ -57,17 +57,19 @@ AccumulatorState& AccumulatorStack::mut_latest() noexcept { return accumulators[
 void AccumulatorStack::reset() noexcept {
     accumulators[0].dirtyPiece = {};
     new (&accumulators[0].dirtyThreats) DirtyThreats;
+    new (&accumulators[0].dirtyPawnPairs) DirtyPawnPairs;
     accumulators[0].computed.fill(false);
     size = 1;
 }
 
-std::pair<DirtyPiece&, DirtyThreats&> AccumulatorStack::push() noexcept {
+Dirties& AccumulatorStack::push() noexcept {
     assert(size < MaxSize);
     auto& st = accumulators[size];
     st.computed.fill(false);
     new (&st.dirtyThreats) DirtyThreats;
+    new (&st.dirtyPawnPairs) DirtyPawnPairs;
     size++;
-    return {st.dirtyPiece, st.dirtyThreats};
+    return st;
 }
 
 void AccumulatorStack::pop() noexcept {
@@ -177,8 +179,8 @@ void apply_combined(Color                              perspective,
     vec_t      acc[Tiling::NumRegs];
     psqt_vec_t psqt[Tiling::NumPsqtRegs];
 
-    const auto* psqWeights    = &featureTransformer.weights[0];
+    const auto* psqWeights         = &featureTransformer.weights[0];
-    const auto* threatWeights = &featureTransformer.threatWeights[0];
+    const auto* threatAndPpWeights = &featureTransformer.threatAndPpWeights[0];
 
     for (IndexType j = 0; j < Dimensions / Tiling::TileHeight; ++j)
     {
@@ -208,7 +210,7 @@ void apply_combined(Color                              perspective,
         for (int i = 0; i < thrRemoved.ssize(); ++i)
         {
             auto* column = reinterpret_cast<const vec_i8_t*>(
-              &threatWeights[thrRemoved[i] * Dimensions + tileOff]);
+              &threatAndPpWeights[thrRemoved[i] * Dimensions + tileOff]);
 
     #ifdef USE_NEON
             for (IndexType k = 0; k < Tiling::NumRegs; k += 2)
@@ -224,8 +226,8 @@ void apply_combined(Color                              perspective,
 
         for (int i = 0; i < thrAdded.ssize(); ++i)
         {
-            auto* column =
+            auto* column = reinterpret_cast<const vec_i8_t*>(
-              reinterpret_cast<const vec_i8_t*>(&threatWeights[thrAdded[i] * Dimensions + tileOff]);
+              &threatAndPpWeights[thrAdded[i] * Dimensions + tileOff]);
 
     #ifdef USE_NEON
             for (IndexType k = 0; k < Tiling::NumRegs; k += 2)
@@ -271,7 +273,8 @@ void apply_combined(Color                              perspective,
         for (int i = 0; i < thrRemoved.ssize(); ++i)
         {
             auto* columnPsqt = reinterpret_cast<const psqt_vec_t*>(
-              &featureTransformer.threatPsqtWeights[thrRemoved[i] * PSQTBuckets + psqtTileOff]);
+              &featureTransformer
+                 .threatAndPpPsqtWeights[thrRemoved[i] * PSQTBuckets + psqtTileOff]);
             for (usize k = 0; k < Tiling::NumPsqtRegs; ++k)
                 psqt[k] = vec_sub_psqt_32(psqt[k], columnPsqt[k]);
         }
@@ -279,7 +282,7 @@ void apply_combined(Color                              perspective,
         for (int i = 0; i < thrAdded.ssize(); ++i)
         {
             auto* columnPsqt = reinterpret_cast<const psqt_vec_t*>(
-              &featureTransformer.threatPsqtWeights[thrAdded[i] * PSQTBuckets + psqtTileOff]);
+              &featureTransformer.threatAndPpPsqtWeights[thrAdded[i] * PSQTBuckets + psqtTileOff]);
             for (usize k = 0; k < Tiling::NumPsqtRegs; ++k)
                 psqt[k] = vec_add_psqt_32(psqt[k], columnPsqt[k]);
         }
@@ -293,9 +296,9 @@ void apply_combined(Color                              perspective,
     usize tileOffset = 0;
 
     const auto* psqWeights        = &featureTransformer.weights[0];
-    const auto* threatWeights     = &featureTransformer.threatWeights[0];
+    const auto* threatWeights     = &featureTransformer.threatAndPpWeights[0];
     const auto* psqtWeights       = &featureTransformer.psqtWeights[0];
-    const auto* threatPsqtWeights = &featureTransformer.threatPsqtWeights[0];
+    const auto* threatPsqtWeights = &featureTransformer.threatAndPpPsqtWeights[0];
 
     while (tileOffset < Dimensions)
     {
@@ -373,18 +376,18 @@ void apply_combined(Color                              perspective,
     {
         const IndexType offset = Dimensions * index;
         for (IndexType j = 0; j < Dimensions; ++j)
-            toAcc[j] -= featureTransformer.threatWeights[offset + j];
+            toAcc[j] -= featureTransformer.threatAndPpWeights[offset + j];
         for (usize k = 0; k < PSQTBuckets; ++k)
-            toPsqtAcc[k] -= featureTransformer.threatPsqtWeights[index * PSQTBuckets + k];
+            toPsqtAcc[k] -= featureTransformer.threatAndPpPsqtWeights[index * PSQTBuckets + k];
     }
 
     for (const auto index : thrAdded)
     {
         const IndexType offset = Dimensions * index;
         for (IndexType j = 0; j < Dimensions; ++j)
-            toAcc[j] += featureTransformer.threatWeights[offset + j];
+            toAcc[j] += featureTransformer.threatAndPpWeights[offset + j];
         for (usize k = 0; k < PSQTBuckets; ++k)
-            toPsqtAcc[k] += featureTransformer.threatPsqtWeights[index * PSQTBuckets + k];
+            toPsqtAcc[k] += featureTransformer.threatAndPpPsqtWeights[index * PSQTBuckets + k];
     }
 
 #endif
@@ -407,22 +410,28 @@ void update_accumulator_incremental(Color                     perspective,
     PSQFeatureSet::IndexList    psqRemoved, psqAdded;
     ThreatFeatureSet::IndexList thrRemoved, thrAdded;
 
-    const auto& dirtyPiece   = Forward ? target_state.dirtyPiece : computed.dirtyPiece;
+    const auto& dirtyPiece     = Forward ? target_state.dirtyPiece : computed.dirtyPiece;
-    const auto& dirtyThreats = Forward ? target_state.dirtyThreats : computed.dirtyThreats;
+    const auto& dirtyThreats   = Forward ? target_state.dirtyThreats : computed.dirtyThreats;
+    const auto& dirtyPawnPairs = Forward ? target_state.dirtyPawnPairs : computed.dirtyPawnPairs;
 
-    const auto* pfBase   = &featureTransformer.threatWeights[0];
+    // Used solely for prefetching
-    IndexType   pfStride = FeatureTransformer::OutputDimensions;
+    const auto* threatPpBase = &featureTransformer.threatAndPpWeights[0];
+    IndexType   pfStride     = FeatureTransformer::OutputDimensions;
 
     if constexpr (Forward)
     {
         ThreatFeatureSet::append_changed_indices(perspective, ksq, dirtyThreats, thrRemoved,
-                                                 thrAdded, pfBase, pfStride);
+                                                 thrAdded, threatPpBase, pfStride);
+        PairFeatureSet::append_changed_indices(perspective, ksq, dirtyPawnPairs, thrRemoved,
+                                               thrAdded, threatPpBase, pfStride);
         PSQFeatureSet::append_changed_indices(perspective, ksq, dirtyPiece, psqRemoved, psqAdded);
     }
     else
     {
         ThreatFeatureSet::append_changed_indices(perspective, ksq, dirtyThreats, thrAdded,
-                                                 thrRemoved, pfBase, pfStride);
+                                                 thrRemoved, threatPpBase, pfStride);
+        PairFeatureSet::append_changed_indices(perspective, ksq, dirtyPawnPairs, thrAdded,
+                                               thrRemoved, threatPpBase, pfStride);
         PSQFeatureSet::append_changed_indices(perspective, ksq, dirtyPiece, psqAdded, psqRemoved);
     }
 
@@ -575,6 +584,7 @@ void update_accumulator_refresh_cache(Color                     perspective,
 
     ThreatFeatureSet::IndexList active;
     ThreatFeatureSet::append_active_indices(perspective, pos, active);
+    PairFeatureSet::append_active_indices(perspective, pos, active);
 
     accumulator.computed[perspective] = true;
 
@@ -582,8 +592,8 @@ void update_accumulator_refresh_cache(Color                     perspective,
     vec_t      acc[Tiling::NumRegs];
     psqt_vec_t psqt[Tiling::NumPsqtRegs];
 
-    const auto* weights       = &featureTransformer.weights[0];
+    const auto* weights            = &featureTransformer.weights[0];
-    const auto* threatWeights = &featureTransformer.threatWeights[0];
+    const auto* threatAndPpWeights = &featureTransformer.threatAndPpWeights[0];
 
     for (IndexType j = 0; j < Dimensions / Tiling::TileHeight; ++j)
     {
@@ -614,8 +624,8 @@ void update_accumulator_refresh_cache(Color                     perspective,
 
         for (int i = 0; i < active.ssize(); ++i)
         {
-            auto* column =
+            auto* column = reinterpret_cast<const vec_i8_t*>(
-              reinterpret_cast<const vec_i8_t*>(&threatWeights[active[i] * Dimensions + tileOff]);
+              &threatAndPpWeights[active[i] * Dimensions + tileOff]);
 
     #ifdef USE_NEON
             for (IndexType k = 0; k < Tiling::NumRegs; k += 2)
@@ -664,7 +674,7 @@ void update_accumulator_refresh_cache(Color                     perspective,
         for (int i = 0; i < active.ssize(); ++i)
         {
             auto* columnPsqt = reinterpret_cast<const psqt_vec_t*>(
-              &featureTransformer.threatPsqtWeights[active[i] * PSQTBuckets + psqtTileOff]);
+              &featureTransformer.threatAndPpPsqtWeights[active[i] * PSQTBuckets + psqtTileOff]);
             for (usize k = 0; k < Tiling::NumPsqtRegs; ++k)
                 psqt[k] = vec_add_psqt_32(psqt[k], columnPsqt[k]);
         }
@@ -676,9 +686,9 @@ void update_accumulator_refresh_cache(Color                     perspective,
 #elif defined(USE_RVV)
 
     const auto* weights           = &featureTransformer.weights[0];
-    const auto* threatWeights     = &featureTransformer.threatWeights[0];
+    const auto* threatWeights     = &featureTransformer.threatAndPpWeights[0];
     const auto* psqtWeights       = &featureTransformer.psqtWeights[0];
-    const auto* threatPsqtWeights = &featureTransformer.threatPsqtWeights[0];
+    const auto* threatPsqtWeights = &featureTransformer.threatAndPpPsqtWeights[0];
 
     usize tileOffset = 0;
 
@@ -763,11 +773,11 @@ void update_accumulator_refresh_cache(Color                     perspective,
 
         for (IndexType j = 0; j < Dimensions; ++j)
             accumulator.accumulation[perspective][j] +=
-              featureTransformer.threatWeights[offset + j];
+              featureTransformer.threatAndPpWeights[offset + j];
 
         for (usize k = 0; k < PSQTBuckets; ++k)
             accumulator.psqtAccumulation[perspective][k] +=
-              featureTransformer.threatPsqtWeights[index * PSQTBuckets + k];
+              featureTransformer.threatAndPpPsqtWeights[index * PSQTBuckets + k];
     }
 
 #endif

src/nnue/nnue_accumulator.h

@@ -24,7 +24,6 @@
 #include <array>
 #include <cstddef>
 #include <cstring>
-#include <utility>
 
 #include "../types.h"
 #include "../misc.h"
@@ -90,10 +89,7 @@ struct AccumulatorCaches {
 };
 
 
-struct AccumulatorState: public Accumulator {
+struct AccumulatorState: public Accumulator, Dirties {};
-    DirtyPiece   dirtyPiece;
-    DirtyThreats dirtyThreats;
-};
 
 class AccumulatorStack {
    public:
@@ -101,9 +97,9 @@ class AccumulatorStack {
 
     [[nodiscard]] const AccumulatorState& latest() const noexcept;
 
-    void                                  reset() noexcept;
+    void     reset() noexcept;
-    std::pair<DirtyPiece&, DirtyThreats&> push() noexcept;
+    Dirties& push() noexcept;
-    void                                  pop() noexcept;
+    void     pop() noexcept;
 
     void evaluate(const Position&           pos,
                   const FeatureTransformer& featureTransformer,

src/nnue/nnue_architecture.h

@@ -26,6 +26,7 @@
 
 #include "features/half_ka_v2_hm.h"
 #include "features/full_threats.h"
+#include "features/pp_3wide.h"
 #include "layers/affine_transform.h"
 #include "layers/affine_transform_sparse_input.h"
 #include "layers/clipped_relu.h"
@@ -37,6 +38,7 @@ namespace Stockfish::Eval::NNUE {
 
 // Input features used in evaluation function
 using ThreatFeatureSet = Features::FullThreats;
+using PairFeatureSet   = Features::PP_3Wide;
 using PSQFeatureSet    = Features::HalfKAv2_hm;
 
 // Number of input feature dimensions after conversion

src/nnue/nnue_common.h

@@ -187,12 +187,9 @@ inline void write_little_endian(std::ostream& stream, const IntType* values, usi
 // Read N signed integers from the stream s, putting them in the array out.
 // The stream is assumed to be compressed using the signed LEB128 format.
 // See https://en.wikipedia.org/wiki/LEB128 for a description of the compression scheme.
-template<typename BufType, typename IntType, usize Count>
+template<typename BufType, typename IntType>
-inline void read_leb_128_detail(std::istream&               stream,
+inline void read_leb_128_detail(
-                                std::array<IntType, Count>& out,
+  std::istream& stream, IntType* out, usize Count, u32& bytes_left, BufType& buf, u32& buf_pos) {
-                                u32&                        bytes_left,
-                                BufType&                    buf,
-                                u32&                        buf_pos) {
 
     static_assert(std::is_signed_v<IntType>, "Not implemented for unsigned types");
     static_assert(sizeof(IntType) <= 4, "Not implemented for types larger than 32 bit");
@@ -233,7 +230,24 @@ inline void read_leb_128(std::istream& stream, Arrays&... outs) {
     std::array<u8, 8192> buf;
     u32                  buf_pos = u32(buf.size());
 
-    (read_leb_128_detail(stream, outs, bytes_left, buf, buf_pos), ...);
+    (read_leb_128_detail(stream, outs.data(), outs.size(), bytes_left, buf, buf_pos), ...);
+
+    assert(bytes_left == 0);
+}
+
+
+template<typename IntType>
+inline void read_leb_128(std::istream& stream, IntType* out, usize expected) {
+    // Check the presence of our LEB128 magic string
+    char leb128MagicString[Leb128MagicStringSize];
+    stream.read(leb128MagicString, Leb128MagicStringSize);
+    assert(strncmp(Leb128MagicString, leb128MagicString, Leb128MagicStringSize) == 0);
+
+    auto                 bytes_left = read_little_endian<u32>(stream);
+    std::array<u8, 8192> buf;
+    u32                  buf_pos = u32(buf.size());
+
+    read_leb_128_detail(stream, out, expected, bytes_left, buf, buf_pos);
 
     assert(bytes_left == 0);
 }
@@ -243,8 +257,8 @@ inline void read_leb_128(std::istream& stream, Arrays&... outs) {
 // This takes N integers from array values, compresses them with
 // the LEB128 algorithm and writes the result on the stream s.
 // See https://en.wikipedia.org/wiki/LEB128 for a description of the compression scheme.
-template<typename IntType, usize Count>
+template<typename IntType>
-inline void write_leb_128(std::ostream& stream, const std::array<IntType, Count>& values) {
+inline void write_leb_128(std::ostream& stream, const IntType* values, usize Count) {
 
     // Write our LEB128 magic string
     stream.write(Leb128MagicString, Leb128MagicStringSize);
@@ -303,6 +317,11 @@ inline void write_leb_128(std::ostream& stream, const std::array<IntType, Count>
     flush();
 }
 
+template<typename IntType, usize Count>
+inline void write_leb_128(std::ostream& stream, const std::array<IntType, Count>& values) {
+    write_leb_128(stream, values.data(), Count);
+}
+
 }  // namespace Stockfish::Eval::NNUE
 
 #endif  // #ifndef NNUE_COMMON_H_INCLUDED

src/nnue/nnue_feature_transformer.h

@@ -87,7 +87,9 @@ class FeatureTransformer {
 
     // Number of input/output dimensions
     static constexpr IndexType ThreatInputDimensions = ThreatFeatureSet::Dimensions;
-    static constexpr IndexType InputDimensions  = PSQFeatureSet::Dimensions + ThreatInputDimensions;
+    static constexpr IndexType PairInputDimensions   = PairFeatureSet::Dimensions;
+    static constexpr IndexType InputDimensions =
+      PSQFeatureSet::Dimensions + ThreatInputDimensions + PairInputDimensions;
     static constexpr IndexType OutputDimensions = HalfDimensions;
 
     // Size of forward propagation buffer
@@ -128,7 +130,8 @@ class FeatureTransformer {
 
     // Hash value embedded in the evaluation file
     static constexpr u32 get_hash_value() {
-        return combine_hash({ThreatFeatureSet::HashValue, PSQFeatureSet::HashValue})
+        return combine_hash(
+                 {ThreatFeatureSet::HashValue, PairFeatureSet::HashValue, PSQFeatureSet::HashValue})
              ^ (OutputDimensions * 2);
     }
 
@@ -136,22 +139,42 @@ class FeatureTransformer {
         permute<16>(biases, PackusEpi16Order);
         permute<16>(weights, PackusEpi16Order);
 
-        permute<8>(threatWeights, PackusEpi16Order);
+        permute<8>(threatAndPpWeights, PackusEpi16Order);
     }
 
     void unpermute_weights() {
         permute<16>(biases, InversePackusEpi16Order);
         permute<16>(weights, InversePackusEpi16Order);
-        permute<8>(threatWeights, InversePackusEpi16Order);
+        permute<8>(threatAndPpWeights, InversePackusEpi16Order);
     }
 
+    auto threatWeights() { return threatAndPpWeights.data(); }
+    auto threatWeights() const { return threatAndPpWeights.data(); }
+    auto ppWeights() { return &threatAndPpWeights[ThreatFeatureSet::Dimensions * HalfDimensions]; }
+    auto ppWeights() const {
+        return &threatAndPpWeights[ThreatFeatureSet::Dimensions * HalfDimensions];
+    }
+
+    auto threatPsqtWeights() { return threatAndPpPsqtWeights.data(); }
+    auto threatPsqtWeights() const { return threatAndPpPsqtWeights.data(); }
+    auto ppPsqtWeights() {
+        return &threatAndPpPsqtWeights[ThreatFeatureSet::Dimensions * PSQTBuckets];
+    }
+    auto ppPsqtWeights() const {
+        return &threatAndPpPsqtWeights[ThreatFeatureSet::Dimensions * PSQTBuckets];
+    }
+
+
     // Read network parameters
     bool read_parameters(std::istream& stream) {
         read_leb_128(stream, biases);
 
-        read_little_endian<ThreatWeightType>(stream, threatWeights.data(),
+        read_little_endian<ThreatWeightType>(stream, threatWeights(),
                                              ThreatInputDimensions * HalfDimensions);
-        read_leb_128(stream, threatPsqtWeights);
+        read_leb_128(stream, threatPsqtWeights(), ThreatFeatureSet::Dimensions * PSQTBuckets);
+        read_little_endian<ThreatWeightType>(stream, ppWeights(),
+                                             PairInputDimensions * HalfDimensions);
+        read_leb_128(stream, ppPsqtWeights(), PairFeatureSet::Dimensions * PSQTBuckets);
 
         read_leb_128(stream, weights);
         read_leb_128(stream, psqtWeights);
@@ -170,9 +193,14 @@ class FeatureTransformer {
         write_leb_128<BiasType>(stream, copy->biases);
 
 
-        write_little_endian<ThreatWeightType>(stream, copy->threatWeights.data(),
+        write_little_endian<ThreatWeightType>(stream, copy->threatWeights(),
                                               ThreatInputDimensions * HalfDimensions);
-        write_leb_128<PSQTWeightType>(stream, copy->threatPsqtWeights);
+        write_leb_128<PSQTWeightType>(stream, copy->threatPsqtWeights(),
+                                      ThreatFeatureSet::Dimensions * PSQTBuckets);
+        write_little_endian<ThreatWeightType>(stream, copy->ppWeights(),
+                                              PairInputDimensions * HalfDimensions);
+        write_leb_128<PSQTWeightType>(stream, copy->ppPsqtWeights(),
+                                      PairFeatureSet::Dimensions * PSQTBuckets);
 
         write_leb_128<WeightType>(stream, copy->weights);
         write_leb_128<PSQTWeightType>(stream, copy->psqtWeights);
@@ -187,8 +215,8 @@ class FeatureTransformer {
         hash_combine(h, get_raw_data_hash(weights));
         hash_combine(h, get_raw_data_hash(psqtWeights));
 
-        hash_combine(h, get_raw_data_hash(threatWeights));
+        hash_combine(h, get_raw_data_hash(threatAndPpWeights));
-        hash_combine(h, get_raw_data_hash(threatPsqtWeights));
+        hash_combine(h, get_raw_data_hash(threatAndPpPsqtWeights));
 
         hash_combine(h, get_hash_value());
 
@@ -399,12 +427,20 @@ class FeatureTransformer {
     alignas(CacheLineSize) std::array<BiasType, HalfDimensions> biases;
     alignas(
       CacheLineSize) std::array<WeightType, HalfDimensions * PSQFeatureSet::Dimensions> weights;
+
+    // Threats and pawn-pair features are concatenated into one array to allow for a single index to address either.
+    // The first pawn-pair feature is at index ThreatFeatureSet::Dimensions.
+    static_assert(PairFeatureSet::IndexBase == ThreatFeatureSet::Dimensions);
+
+    alignas(CacheLineSize) std::array<ThreatWeightType,
+                                      (ThreatFeatureSet::Dimensions + PairFeatureSet::Dimensions)
+                                        * HalfDimensions> threatAndPpWeights;
     alignas(CacheLineSize)
-      std::array<ThreatWeightType, HalfDimensions * ThreatFeatureSet::Dimensions> threatWeights;
+      std::array<PSQTWeightType, PSQTBuckets * PSQFeatureSet::Dimensions> psqtWeights;
-    alignas(CacheLineSize)
+    // As above
-      std::array<PSQTWeightType, PSQFeatureSet::Dimensions * PSQTBuckets> psqtWeights;
+    alignas(CacheLineSize) std::array<PSQTWeightType,
-    alignas(CacheLineSize)
+                                      (ThreatFeatureSet::Dimensions + PairFeatureSet::Dimensions)
-      std::array<PSQTWeightType, ThreatFeatureSet::Dimensions * PSQTBuckets> threatPsqtWeights;
+                                        * PSQTBuckets> threatAndPpPsqtWeights;
 };
 
 }  // namespace Stockfish::Eval::NNUE

src/position.cpp

@@ -817,8 +817,7 @@ bool Position::gives_check(Move m) const {
 void Position::do_move(Move                      m,
                        StateInfo&                newSt,
                        bool                      givesCheck,
-                       DirtyPiece&               dp,
+                       Dirties&                  dirties,
-                       DirtyThreats&             dts,
                        const TranspositionTable* tt      = nullptr,
                        const SharedHistories*    history = nullptr) {
 
@@ -840,6 +839,13 @@ void Position::do_move(Move                      m,
     ++st->rule50;
     ++st->pliesFromNull;
 
+    auto& dpps = dirties.dirtyPawnPairs;
+    auto& dts  = dirties.dirtyThreats;
+    auto& dp   = dirties.dirtyPiece;
+
+    dpps.before[WHITE] = pieces(WHITE, PAWN);
+    dpps.before[BLACK] = pieces(BLACK, PAWN);
+
     Color  us       = sideToMove;
     Color  them     = ~us;
     Square from     = m.from_sq();
@@ -1065,6 +1071,9 @@ void Position::do_move(Move                      m,
 
     assert(pos_is_ok());
 
+    dpps.after[WHITE] = pieces(WHITE, PAWN);
+    dpps.after[BLACK] = pieces(BLACK, PAWN);
+
     assert(dp.pc != NO_PIECE);
     assert(!(bool(captured) || m.type_of() == CASTLING) ^ (dp.remove_sq != SQ_NONE));
     assert(dp.from != SQ_NONE);
@@ -1238,32 +1247,14 @@ void Position::update_piece_threats(Piece               pc,
     Bitboard threatened       = attacks_bb(pc, s, occupied) & occupiedNoK;
     Bitboard incoming_threats = PseudoAttacks[KNIGHT][s] & knights;
 
-    // Compute both incoming and outgoing pawn threats. Incoming pawn pushers are only
+    if (type_of(pc) == KNIGHT || type_of(pc) == ROOK)
-    // added if 'pc' is a pawn.
+        incoming_threats |=
-    Bitboard pawnThreats = 0;
-    if (type_of(pc) == PAWN)
-    {
-        Bitboard whiteAttacks = PawnPushOrAttacks[WHITE][s];
-        Bitboard blackAttacks = PawnPushOrAttacks[BLACK][s];
-
-        threatened |= (color_of(pc) == WHITE ? whiteAttacks : blackAttacks) & pieces(PAWN);
-
-        pawnThreats = whiteAttacks & blackPawns;
-        pawnThreats |= blackAttacks & whitePawns;
-    }
-    else
-    {
-        pawnThreats =
           (attacks_bb<PAWN>(s, WHITE) & blackPawns) | (attacks_bb<PAWN>(s, BLACK) & whitePawns);
-    }
-
-    if (type_of(pc) == PAWN || type_of(pc) == KNIGHT || type_of(pc) == ROOK)
-        incoming_threats |= pawnThreats;
 
     switch (type_of(pc))
     {
     case PAWN :
-        threatened &= pieces(PAWN, KNIGHT, ROOK);
+        threatened &= pieces(KNIGHT, ROOK);
         break;
     case BISHOP :
     case ROOK :

src/position.h

@@ -147,8 +147,7 @@ class Position {
     void do_move(Move                      m,
                  StateInfo&                newSt,
                  bool                      givesCheck,
-                 DirtyPiece&               dp,
+                 Dirties&                  dirties,
-                 DirtyThreats&             dts,
                  const TranspositionTable* tt,
                  const SharedHistories*    worker);
     void undo_move(Move m);
@@ -221,16 +220,15 @@ class Position {
     std::array<Bitboard, PIECE_TYPE_NB> byTypeBB;
     std::array<Bitboard, COLOR_NB>      byColorBB;
 
-    int          pieceCount[PIECE_NB];
+    int        pieceCount[PIECE_NB];
-    int          castlingRightsMask[SQUARE_NB];
+    int        castlingRightsMask[SQUARE_NB];
-    Square       castlingRookSquare[CASTLING_RIGHT_NB];
+    Square     castlingRookSquare[CASTLING_RIGHT_NB];
-    Bitboard     castlingPath[CASTLING_RIGHT_NB];
+    Bitboard   castlingPath[CASTLING_RIGHT_NB];
-    StateInfo*   st;
+    StateInfo* st;
-    int          gamePly;
+    int        gamePly;
-    Color        sideToMove;
+    Color      sideToMove;
-    bool         chess960;
+    bool       chess960;
-    DirtyPiece   scratch_dp;
+    Dirties    scratchDirties;
-    DirtyThreats scratch_dts;
 };
 
 std::ostream& operator<<(std::ostream& os, const Position& pos);
@@ -437,8 +435,9 @@ inline void Position::swap_piece(Square s, Piece pc, DirtyThreats* const dts) {
 }
 
 inline void Position::do_move(Move m, StateInfo& newSt, const TranspositionTable* tt = nullptr) {
-    new (&scratch_dts) DirtyThreats;
+    new (&scratchDirties.dirtyThreats) DirtyThreats;
-    do_move(m, newSt, gives_check(m), scratch_dp, scratch_dts, tt, nullptr);
+    new (&scratchDirties.dirtyPawnPairs) DirtyPawnPairs;
+    do_move(m, newSt, gives_check(m), scratchDirties, tt, nullptr);
 }
 
 inline StateInfo* Position::state() const { return st; }

src/search.cpp

@@ -644,12 +644,13 @@ void Search::Worker::do_move(
     bool capture = pos.capture_stage(move);
     ++nodes;
 
-    auto [dirtyPiece, dirtyThreats] = accumulatorStack.push();
+    Dirties& dirties = accumulatorStack.push();
-    pos.do_move(move, st, givesCheck, dirtyPiece, dirtyThreats, &tt, &sharedHistory);
+    pos.do_move(move, st, givesCheck, dirties, &tt, &sharedHistory);
 
     if (ss != nullptr)
     {
-        ss->currentMove = move;
+        auto& dirtyPiece = dirties.dirtyPiece;
+        ss->currentMove  = move;
         ss->continuationHistory =
           &continuationHistory[ss->inCheck][capture][dirtyPiece.pc][move.to_sq()];
         ss->continuationCorrectionHistory =

src/types.h

@@ -344,6 +344,17 @@ struct DirtyThreats {
     DirtyThreatList list;
 };
 
+struct DirtyPawnPairs {
+    Bitboard before[COLOR_NB];
+    Bitboard after[COLOR_NB];
+};
+
+struct Dirties {
+    DirtyPiece     dirtyPiece;
+    DirtyThreats   dirtyThreats;
+    DirtyPawnPairs dirtyPawnPairs;
+};
+
     #define ENABLE_INCR_OPERATORS_ON(T) \
         constexpr T& operator++(T& d) { return d = T(int(d) + 1); } \
         constexpr T& operator--(T& d) { return d = T(int(d) - 1); }