Stockfish 18

Official release version of Stockfish 18

Bench: 2050811

---

Stockfish 18

Today, we have the pleasure of announcing Stockfish 18, a new major release. As
always, you can freely download it at [stockfishchess.org/download][1] and use
it as a drop-in replacement in the [GUI of your choice][2] to benefit from
stronger play and more accurate analysis.

Whether you can spare hours or days of CPU time, your help matters for the
ongoing development of Stockfish. Find out how you can help at
[stockfishchess.org/get-involved][3]. Join our [Discord server][4] to get in
touch with the community of developers and users of the project!

Quality of chess play

In tests against Stockfish 17, this new release brings an Elo gain of up to [46
points][5], and wins [four times as many game pairs][6] as it loses. Quality
improved throughout, including in [Fischer Random Chess][7].

Stockfish is stronger than any human, even when running on older or low-end
hardware. On the highest-end hardware, where Stockfish can search over [500
million positions per second][8], it continues to [dominate chess engine
tournaments][9].

Update highlights

Next-Generation Evaluation

This release introduces the SFNNv10 network architecture. The network’s input
layer has been augmented with 'Threat Inputs' features as part of a massive
community effort. These features allow the engine to 'see' which pieces are
threatened more naturally, resulting in more accurate evaluations.

Hardware and Performance Optimizations

A key highlight is the new 'Shared Memory' implementation, which allows
different Stockfish processes to share the same memory space for neural network
weights. This makes it the most efficient version for cloud analysis and
high-concurrency testing.

Significant efforts have also been made to utilize hardware more effectively by
adapting the code to make use of modern CPU instructions and refining how
threads interact during a search.

Search Improvements

Stockfish 18 features a heavily refined search, utilizing 'Correction History'
to dynamically adjust evaluations based on patterns found during the search
itself. These and other refinements allow the engine to detect stalemates and
evaluate fortresses significantly better than previous versions. A particularly
rare issue, involving threefold repetition detection, en passant, and pins, was
also fixed.

Refactored Training Workflow

The training of Stockfish's neural networks has transitioned to an automated
and reproducible model. This new framework allows the project to employ
standardized recipes to chain complex training stages together. This transition
facilitates the training of networks using over 100 billion positions of [Lc0
evaluation data][10].

Thank you

In this release in particular, we are deeply grateful to the contributors who
shared their research and ideas to help develop the new threat-input network
architecture.

The Stockfish project builds on a thriving community of enthusiasts (thanks to
everybody!) who contribute their expertise, time, and resources to build a free
and open-source chess engine that is robust, widely available, and very strong.

We would like to express our gratitude for the [14.6k stars][11] that light up
our GitHub project. Thank you for your support and encouragement – your
recognition means a lot to us. Programmers can contribute to the project either
directly to [Stockfish][12] (C++), to [Fishtest][13] (HTML, CSS, JavaScript,
and Python), to our trainer [nnue-pytorch][14] (C++ and Python), or to our
[website][15] (HTML, CSS/SCSS, and JavaScript).

The Stockfish team

[1]: https://stockfishchess.org/download
[2]: https://official-stockfish.github.io/docs/stockfish-wiki/Download-and-usage.html#download-a-chess-gui
[3]: https://stockfishchess.org/get-involved/
[4]: https://discord.gg/GWDRS3kU6R
[5]: https://tests.stockfishchess.org/tests/view/696a9e15cec152c6220c1d19
[6]: https://tests.stockfishchess.org/tests/view/696a9e4dcec152c6220c1d1b
[7]: https://tests.stockfishchess.org/tests/view/696a9e83cec152c6220c1d1d
[8]: https://openbenchmarking.org/test/pts/stockfish
[9]: https://en.wikipedia.org/wiki/Stockfish_(chess)#Competition_results
[10]: https://lczero.org/blog/2021/06/the-importance-of-open-data/
[11]: https://github.com/official-stockfish/Stockfish/stargazers
[12]: https://github.com/official-stockfish/Stockfish
[13]: https://github.com/official-stockfish/fishtest
[14]: https://github.com/official-stockfish/nnue-pytorch
[15]: https://github.com/official-stockfish/stockfish-web

.github/workflows/avx2_compilers.yml

@@ -0,0 +1,85 @@
+name: AVX2 Compiler Matrix
+
+on:
+  workflow_call:
+
+jobs:
+  avx2-compiler-matrix:
+    name: avx2 (${{ matrix.name }})
+    runs-on: ubuntu-latest
+    container:
+      image: ${{ matrix.image }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - { name: gcc-10, comp: gcc, cxx: g++, image: "gcc:10" }
+          - { name: gcc-11, comp: gcc, cxx: g++, image: "gcc:11" }
+          - { name: gcc-12, comp: gcc, cxx: g++, image: "gcc:12" }
+          - { name: gcc-13, comp: gcc, cxx: g++, image: "gcc:13" }
+          - { name: gcc-14, comp: gcc, cxx: g++, image: "gcc:14" }
+          - { name: gcc-15, comp: gcc, cxx: g++, image: "gcc:15" }
+
+          # Using silkeh/clang for older versions
+          - { name: clang-10, comp: clang, cxx: clang++, image: "silkeh/clang:10", is_clang: true, ver: "10" }
+          - { name: clang-11, comp: clang, cxx: clang++, image: "silkeh/clang:11", is_clang: true, ver: "11" }
+          - { name: clang-12, comp: clang, cxx: clang++, image: "silkeh/clang:12", is_clang: true, ver: "12" }
+          - { name: clang-13, comp: clang, cxx: clang++, image: "silkeh/clang:13", is_clang: true, ver: "13" }
+          - { name: clang-14, comp: clang, cxx: clang++, image: "silkeh/clang:14", is_clang: true, ver: "14" }
+          - { name: clang-15, comp: clang, cxx: clang++, image: "silkeh/clang:15", is_clang: true, ver: "15" }
+          - { name: clang-16, comp: clang, cxx: clang++, image: "silkeh/clang:16", is_clang: true, ver: "16" }
+          - { name: clang-17, comp: clang, cxx: clang++, image: "silkeh/clang:17", is_clang: true, ver: "17" }
+
+          - { name: clang-18, comp: clang, cxx: clang++-18, image: "ubuntu:rolling", is_clang: true, ver: "18" }
+          - { name: clang-19, comp: clang, cxx: clang++-19, image: "ubuntu:rolling", is_clang: true, ver: "19" }
+          - { name: clang-20, comp: clang, cxx: clang++-20, image: "ubuntu:rolling", is_clang: true, ver: "20" }
+          - { name: clang-21, comp: clang, cxx: clang++-21, image: "ubuntu:rolling", is_clang: true, ver: "21" }
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: |
+          if grep -q "buster" /etc/os-release; then
+            echo "Debian Buster detected. Switching to archive repositories..."
+            echo "deb http://archive.debian.org/debian buster main contrib non-free" > /etc/apt/sources.list
+            echo "deb http://archive.debian.org/debian-security buster/updates main contrib non-free" >> /etc/apt/sources.list
+            echo 'Acquire::Check-Valid-Until "false";' > /etc/apt/apt.conf.d/99-ignore-valid-until
+          fi
+
+          apt-get update
+          apt-get install -y curl git make
+
+      - name: Set up Clang
+        if: ${{ matrix.is_clang && matrix.image == 'ubuntu:rolling' }}
+        run: |
+          if [ "${{ matrix.ver }}" -le 20 ]; then
+            apt-get install -y clang-${{ matrix.ver }}
+          else
+            apt-get install -y \
+              clang-${{ matrix.ver }} \
+              llvm-${{ matrix.ver }}-dev \
+              llvm-${{ matrix.ver }}-linker-tools \
+              lld-${{ matrix.ver }}
+          fi
+
+      - name: Download network
+        working-directory: src
+        run: make net
+
+      - name: Build avx2 binary
+        working-directory: src
+        run: |
+          export CXXFLAGS="-Werror"
+          if [ "${{ matrix.ver }}" -ge 20 ]; then
+            export LDFLAGS="-fuse-ld=lld"
+            apt install -y lld
+          fi
+          make clean
+          make -j build ARCH=x86-64-avx2 COMP=${{ matrix.comp }} COMPCXX=${{ matrix.cxx }}
+
+      - name: Smoke test
+        working-directory: src
+        run: ./stockfish bench 16 1 6

.github/workflows/stockfish.yml

@@ -120,3 +120,5 @@ jobs:
       contents: write # For deleting/creating a (pre)release
     secrets:
       token: ${{ secrets.GITHUB_TOKEN }}
+  CompilerCheck:
+    uses: ./.github/workflows/avx2_compilers.yml

AUTHORS

@@ -111,6 +111,7 @@ Hongzhi Cheng
 Ivan Ivec (IIvec)
 Jacques B. (Timshel)
 Jake Senne (w1wwwwww)
+Jakub Ciolek (jake-ciolek)
 Jan Ondruš (hxim)
 Jared Kish (Kurtbusch, kurt22i)
 Jarrod Torriero (DU-jdto)

src/bitboard.cpp

@@ -49,12 +49,15 @@ std::string Bitboards::pretty(Bitboard b) {
 
     std::string s = "+---+---+---+---+---+---+---+---+\n";
 
-    for (Rank r = RANK_8; r >= RANK_1; --r)
+    for (Rank r = RANK_8;; --r)
     {
         for (File f = FILE_A; f <= FILE_H; ++f)
             s += b & make_square(f, r) ? "| X " : "|   ";
 
         s += "| " + std::to_string(1 + r) + "\n+---+---+---+---+---+---+---+---+\n";
+
+        if (r == RANK_1)
+            break;
     }
     s += "  a   b   c   d   e   f   g   h\n";
 

src/engine.cpp

@@ -52,19 +52,21 @@ constexpr auto StartFEN   = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq
 constexpr int  MaxHashMB  = Is64Bit ? 33554432 : 2048;
 int            MaxThreads = std::max(1024, 4 * int(get_hardware_concurrency()));
 
+// The default configuration will attempt to group L3 domains up to 32 threads.
+// This size was found to be a good balance between the Elo gain of increased
+// history sharing and the speed loss from more cross-cache accesses (see
+// PR#6526). The user can always explicitly override this behavior.
+constexpr NumaAutoPolicy DefaultNumaPolicy = BundledL3Policy{32};
+
 Engine::Engine(std::optional<std::string> path) :
     binaryDirectory(path ? CommandLine::get_binary_directory(*path) : ""),
-    numaContext(NumaConfig::from_system()),
+    numaContext(NumaConfig::from_system(DefaultNumaPolicy)),
     states(new std::deque<StateInfo>(1)),
     threads(),
-    networks(
-      numaContext,
-      // Heap-allocate because sizeof(NN::Networks) is large
-      std::make_unique<NN::Networks>(
-        std::make_unique<NN::NetworkBig>(NN::EvalFile{EvalFileDefaultNameBig, "None", ""},
-                                         NN::EmbeddedNNUEType::BIG),
-        std::make_unique<NN::NetworkSmall>(NN::EvalFile{EvalFileDefaultNameSmall, "None", ""},
-                                           NN::EmbeddedNNUEType::SMALL))) {
+    networks(numaContext,
+             // Heap-allocate because sizeof(NN::Networks) is large
+             std::make_unique<NN::Networks>(NN::EvalFile{EvalFileDefaultNameBig, "None", ""},
+                                            NN::EvalFile{EvalFileDefaultNameSmall, "None", ""})) {
 
     pos.set(StartFEN, false, &states->back());
 
@@ -217,12 +219,12 @@ void Engine::set_position(const std::string& fen, const std::vector<std::string>
 void Engine::set_numa_config_from_option(const std::string& o) {
     if (o == "auto" || o == "system")
     {
-        numaContext.set_numa_config(NumaConfig::from_system());
+        numaContext.set_numa_config(NumaConfig::from_system(DefaultNumaPolicy));
     }
     else if (o == "hardware")
     {
         // Don't respect affinity set in the system.
-        numaContext.set_numa_config(NumaConfig::from_system(false));
+        numaContext.set_numa_config(NumaConfig::from_system(DefaultNumaPolicy, false));
     }
     else if (o == "none")
     {

src/misc.cpp

@@ -40,7 +40,7 @@ namespace Stockfish {
 namespace {
 
 // Version number or dev.
-constexpr std::string_view version = "dev";
+constexpr std::string_view version = "18";
 
 // Our fancy logging facility. The trick here is to replace cin.rdbuf() and
 // cout.rdbuf() with two Tie objects that tie cin and cout to a file stream. We

src/misc.h

@@ -34,6 +34,7 @@
 #include <memory>
 #include <string>
 #include <string_view>
+#include <type_traits>
 #include <vector>
 
 #define stringify2(x) #x
@@ -305,24 +306,38 @@ inline uint64_t mul_hi64(uint64_t a, uint64_t b) {
 #endif
 }
 
-
-template<typename T>
-inline void hash_combine(std::size_t& seed, const T& v) {
-    std::hash<T> hasher;
-    seed ^= hasher(v) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
-}
-
-template<>
-inline void hash_combine(std::size_t& seed, const std::size_t& v) {
-    seed ^= v + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+inline std::uint64_t hash_bytes(const char* data, std::size_t size) {
+    // FNV-1a 64-bit
+    const char*   p = data;
+    std::uint64_t h = 14695981039346656037ull;
+    for (std::size_t i = 0; i < size; ++i)
+        h = (h ^ p[i]) * 1099511628211ull;
+    return h;
 }
 
 template<typename T>
 inline std::size_t get_raw_data_hash(const T& value) {
-    return std::hash<std::string_view>{}(
-      std::string_view(reinterpret_cast<const char*>(&value), sizeof(value)));
+    // We must have no padding bytes because we're reinterpreting as char
+    static_assert(std::has_unique_object_representations<T>());
+
+    return static_cast<std::size_t>(
+      hash_bytes(reinterpret_cast<const char*>(&value), sizeof(value)));
 }
 
+template<typename T>
+inline void hash_combine(std::size_t& seed, const T& v) {
+    std::size_t x;
+    // For primitive types we avoid using the default hasher, which may be
+    // nondeterministic across program invocations
+    if constexpr (std::is_integral<T>())
+        x = v;
+    else
+        x = std::hash<T>{}(v);
+    seed ^= x + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+}
+
+inline std::uint64_t hash_string(const std::string& sv) { return hash_bytes(sv.data(), sv.size()); }
+
 template<std::size_t Capacity>
 class FixedString {
    public:
@@ -450,7 +465,7 @@ void move_to_front(std::vector<T>& vec, Predicate pred) {
 template<std::size_t N>
 struct std::hash<Stockfish::FixedString<N>> {
     std::size_t operator()(const Stockfish::FixedString<N>& fstr) const noexcept {
-        return std::hash<std::string_view>{}((std::string_view) fstr);
+        return Stockfish::hash_bytes(fstr.data(), fstr.size());
     }
 };
 

src/movegen.cpp

@@ -47,10 +47,10 @@ template<Direction offset>
 inline Move* splat_pawn_moves(Move* moveList, Bitboard to_bb) {
     alignas(64) static constexpr auto SPLAT_TABLE = [] {
         std::array<Move, 64> table{};
-        for (int8_t i = 0; i < 64; i++)
+        for (int i = 0; i < 64; i++)
         {
-            Square from{std::clamp<int8_t>(i - offset, 0, 63)};
-            table[i] = {Move(from, Square{i})};
+            Square from{uint8_t(std::clamp(i - offset, 0, 63))};
+            table[i] = {Move(from, Square{uint8_t(i)})};
         }
         return table;
     }();
@@ -68,7 +68,7 @@ inline Move* splat_pawn_moves(Move* moveList, Bitboard to_bb) {
 inline Move* splat_moves(Move* moveList, Square from, Bitboard to_bb) {
     alignas(64) static constexpr auto SPLAT_TABLE = [] {
         std::array<Move, 64> table{};
-        for (int8_t i = 0; i < 64; i++)
+        for (uint8_t i = 0; i < 64; i++)
             table[i] = {Move(SQUARE_ZERO, Square{i})};
         return table;
     }();

src/nnue/features/full_threats.cpp

@@ -37,26 +37,6 @@ struct HelperOffsets {
     int cumulativePieceOffset, cumulativeOffset;
 };
 
-// Information on a particular pair of pieces and whether they should be excluded
-struct PiecePairData {
-    // Layout: bits 8..31 are the index contribution of this piece pair, bits 0 and 1 are exclusion info
-    uint32_t data;
-
-    constexpr PiecePairData() :
-        data(0) {}
-
-    constexpr PiecePairData(bool      excluded_pair,
-                            bool      semi_excluded_pair,
-                            IndexType feature_index_base) :
-        data((uint32_t(excluded_pair) << 1) | (uint32_t(semi_excluded_pair && !excluded_pair))
-             | (uint32_t(feature_index_base) << 8)) {}
-
-    // lsb: excluded if from < to; 2nd lsb: always excluded
-    constexpr uint8_t excluded_pair_info() const { return static_cast<uint8_t>(data); }
-
-    constexpr IndexType feature_index_base() const { return static_cast<IndexType>(data >> 8); }
-};
-
 constexpr std::array<Piece, 12> AllPieces = {
   W_PAWN, W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING,
   B_PAWN, B_KNIGHT, B_BISHOP, B_ROOK, B_QUEEN, B_KING,
@@ -173,7 +153,7 @@ constexpr auto helper_offsets = init_threat_offsets().first;
 constexpr auto offsets = init_threat_offsets().second;
 
 constexpr auto init_index_luts() {
-    std::array<std::array<PiecePairData, PIECE_NB>, PIECE_NB> indices{};
+    std::array<std::array<std::array<uint32_t, 2>, PIECE_NB>, PIECE_NB> indices{};
 
     for (Piece attacker : AllPieces)
     {
@@ -189,8 +169,10 @@ constexpr auto init_index_luts() {
                               + (color_of(attacked) * (numValidTargets[attacker] / 2) + map)
                                   * helper_offsets[attacker].cumulativePieceOffset;
 
-            bool excluded               = map < 0;
-            indices[attacker][attacked] = PiecePairData(excluded, semi_excluded, feature);
+            bool excluded                  = map < 0;
+            indices[attacker][attacked][0] = excluded ? FullThreats::Dimensions : feature;
+            indices[attacker][attacked][1] =
+              excluded || semi_excluded ? FullThreats::Dimensions : feature;
         }
     }
 
@@ -200,7 +182,7 @@ constexpr auto init_index_luts() {
 // The final index is calculated from summing data found in these two LUTs, as well
 // as offsets[attacker][from]
 
-// [attacker][attacked]
+// [attacker][attacked][from < to]
 constexpr auto index_lut1 = init_index_luts();
 // [attacker][from][to]
 constexpr auto index_lut2 = index_lut2_array();
@@ -216,17 +198,9 @@ inline sf_always_inline IndexType FullThreats::make_index(
     unsigned    attacker_oriented = attacker ^ swap;
     unsigned    attacked_oriented = attacked ^ swap;
 
-    const auto piecePairData = index_lut1[attacker_oriented][attacked_oriented];
-
-    const bool less_than = from_oriented < to_oriented;
-    if ((piecePairData.excluded_pair_info() + less_than) & 2)
-        return FullThreats::Dimensions;
-
-    const IndexType index = piecePairData.feature_index_base()
-                          + offsets[attacker_oriented][from_oriented]
-                          + index_lut2[attacker_oriented][from_oriented][to_oriented];
-    sf_assume(index < Dimensions);
-    return index;
+    return index_lut1[attacker_oriented][attacked_oriented][from_oriented < to_oriented]
+         + offsets[attacker_oriented][from_oriented]
+         + index_lut2[attacker_oriented][from_oriented][to_oriented];
 }
 
 // Get a list of indices for active features in ascending order

src/nnue/network.h

@@ -28,7 +28,6 @@
 #include <string>
 #include <string_view>
 #include <tuple>
-#include <utility>
 
 #include "../misc.h"
 #include "../types.h"
@@ -130,9 +129,9 @@ using NetworkSmall = Network<SmallNetworkArchitecture, SmallFeatureTransformer>;
 
 
 struct Networks {
-    Networks(std::unique_ptr<NetworkBig>&& nB, std::unique_ptr<NetworkSmall>&& nS) :
-        big(std::move(*nB)),
-        small(std::move(*nS)) {}
+    Networks(EvalFile bigFile, EvalFile smallFile) :
+        big(bigFile, EmbeddedNNUEType::BIG),
+        small(smallFile, EmbeddedNNUEType::SMALL) {}
 
     NetworkBig   big;
     NetworkSmall small;

src/nnue/nnue_common.h

@@ -169,52 +169,56 @@ inline void write_little_endian(std::ostream& stream, const IntType* values, std
             write_little_endian<IntType>(stream, values[i]);
 }
 
-
 // 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 IntType, std::size_t Count>
-inline void read_leb_128(std::istream& stream, std::array<IntType, Count>& out) {
+template<typename BufType, typename IntType, std::size_t Count>
+inline void read_leb_128_detail(std::istream&               stream,
+                                std::array<IntType, Count>& out,
+                                std::uint32_t&              bytes_left,
+                                BufType&                    buf,
+                                std::uint32_t&              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");
+
+    IntType result = 0;
+    size_t  shift = 0, i = 0;
+    while (i < Count)
+    {
+        if (buf_pos == buf.size())
+        {
+            stream.read(reinterpret_cast<char*>(buf.data()),
+                        std::min(std::size_t(bytes_left), buf.size()));
+            buf_pos = 0;
+        }
+
+        std::uint8_t byte = buf[buf_pos++];
+        --bytes_left;
+        result |= (byte & 0x7f) << (shift % 32);
+        shift += 7;
+
+        if ((byte & 0x80) == 0)
+        {
+            out[i++] = (shift >= 32 || (byte & 0x40) == 0) ? result : result | ~((1 << shift) - 1);
+            result   = 0;
+            shift    = 0;
+        }
+    }
+}
+
+template<typename... Arrays>
+inline void read_leb_128(std::istream& stream, Arrays&... outs) {
     // Check the presence of our LEB128 magic string
     char leb128MagicString[Leb128MagicStringSize];
     stream.read(leb128MagicString, Leb128MagicStringSize);
     assert(strncmp(Leb128MagicString, leb128MagicString, Leb128MagicStringSize) == 0);
 
-    static_assert(std::is_signed_v<IntType>, "Not implemented for unsigned types");
+    auto                           bytes_left = read_little_endian<std::uint32_t>(stream);
+    std::array<std::uint8_t, 8192> buf;
+    std::uint32_t                  buf_pos = buf.size();
 
-    const std::uint32_t BUF_SIZE = 4096;
-    std::uint8_t        buf[BUF_SIZE];
-
-    auto bytes_left = read_little_endian<std::uint32_t>(stream);
-
-    std::uint32_t buf_pos = BUF_SIZE;
-    for (std::size_t i = 0; i < Count; ++i)
-    {
-        IntType result = 0;
-        size_t  shift  = 0;
-        do
-        {
-            if (buf_pos == BUF_SIZE)
-            {
-                stream.read(reinterpret_cast<char*>(buf), std::min(bytes_left, BUF_SIZE));
-                buf_pos = 0;
-            }
-
-            std::uint8_t byte = buf[buf_pos++];
-            --bytes_left;
-            result |= (byte & 0x7f) << shift;
-            shift += 7;
-
-            if ((byte & 0x80) == 0)
-            {
-                out[i] = (sizeof(IntType) * 8 <= shift || (byte & 0x40) == 0)
-                         ? result
-                         : result | ~((1 << shift) - 1);
-                break;
-            }
-        } while (shift < sizeof(IntType) * 8);
-    }
+    (read_leb_128_detail(stream, outs, bytes_left, buf, buf_pos), ...);
 
     assert(bytes_left == 0);
 }

src/nnue/nnue_feature_transformer.h

@@ -132,7 +132,7 @@ class FeatureTransformer {
         permute<16>(biases, PackusEpi16Order);
         permute<16>(weights, PackusEpi16Order);
 
-        if (UseThreats)
+        if constexpr (UseThreats)
             permute<8>(threatWeights, PackusEpi16Order);
     }
 
@@ -140,7 +140,7 @@ class FeatureTransformer {
         permute<16>(biases, InversePackusEpi16Order);
         permute<16>(weights, InversePackusEpi16Order);
 
-        if (UseThreats)
+        if constexpr (UseThreats)
             permute<8>(threatWeights, InversePackusEpi16Order);
     }
 
@@ -152,40 +152,26 @@ class FeatureTransformer {
     }
 
     // Read network parameters
-    // TODO: This is ugly. Currently LEB128 on the entire L1 necessitates
-    // reading the weights into a combined array, and then splitting.
     bool read_parameters(std::istream& stream) {
-        read_leb_128<BiasType>(stream, biases);
+        read_leb_128(stream, biases);
 
-        if (UseThreats)
+        if constexpr (UseThreats)
         {
             read_little_endian<ThreatWeightType>(stream, threatWeights.data(),
                                                  ThreatInputDimensions * HalfDimensions);
-            read_leb_128<WeightType>(stream, weights);
+            read_leb_128(stream, weights);
 
-            auto combinedPsqtWeights =
-              std::make_unique<std::array<PSQTWeightType, TotalInputDimensions * PSQTBuckets>>();
-
-            read_leb_128<PSQTWeightType>(stream, *combinedPsqtWeights);
-
-            std::copy(combinedPsqtWeights->begin(),
-                      combinedPsqtWeights->begin() + ThreatInputDimensions * PSQTBuckets,
-                      std::begin(threatPsqtWeights));
-
-            std::copy(combinedPsqtWeights->begin() + ThreatInputDimensions * PSQTBuckets,
-                      combinedPsqtWeights->begin()
-                        + (ThreatInputDimensions + InputDimensions) * PSQTBuckets,
-                      std::begin(psqtWeights));
+            read_leb_128(stream, threatPsqtWeights, psqtWeights);
         }
         else
         {
-            read_leb_128<WeightType>(stream, weights);
-            read_leb_128<PSQTWeightType>(stream, psqtWeights);
+            read_leb_128(stream, weights);
+            read_leb_128(stream, psqtWeights);
         }
 
         permute_weights();
 
-        if (!UseThreats)
+        if constexpr (!UseThreats)
             scale_weights(true);
 
         return !stream.fail();
@@ -197,12 +183,12 @@ class FeatureTransformer {
 
         copy->unpermute_weights();
 
-        if (!UseThreats)
+        if constexpr (!UseThreats)
             copy->scale_weights(false);
 
         write_leb_128<BiasType>(stream, copy->biases);
 
-        if (UseThreats)
+        if constexpr (UseThreats)
         {
             write_little_endian<ThreatWeightType>(stream, copy->threatWeights.data(),
                                                   ThreatInputDimensions * HalfDimensions);
@@ -256,7 +242,7 @@ class FeatureTransformer {
         auto        psqt =
           (psqtAccumulation[perspectives[0]][bucket] - psqtAccumulation[perspectives[1]][bucket]);
 
-        if (UseThreats)
+        if constexpr (UseThreats)
         {
             const auto& threatPsqtAccumulation =
               (threatAccumulatorState.acc<HalfDimensions>()).psqtAccumulation;
@@ -348,7 +334,7 @@ class FeatureTransformer {
     #else
               6;
     #endif
-            if (UseThreats)
+            if constexpr (UseThreats)
             {
                 const vec_t* tin0 =
                   reinterpret_cast<const vec_t*>(&(threatAccumulation[perspectives[p]][0]));
@@ -400,7 +386,7 @@ class FeatureTransformer {
                 BiasType sum1 =
                   accumulation[static_cast<int>(perspectives[p])][j + HalfDimensions / 2];
 
-                if (UseThreats)
+                if constexpr (UseThreats)
                 {
                     BiasType sum0t = threatAccumulation[static_cast<int>(perspectives[p])][j + 0];
                     BiasType sum1t =

src/numa.h

@@ -371,6 +371,50 @@ inline WindowsAffinity get_process_affinity() {
     return affinity;
 }
 
+// Type machinery used to emulate Cache->GroupCount
+
+template<typename T, typename = void>
+struct HasGroupCount: std::false_type {};
+
+template<typename T>
+struct HasGroupCount<T, std::void_t<decltype(std::declval<T>().Cache.GroupCount)>>: std::true_type {
+};
+
+template<typename T, typename Pred, std::enable_if_t<HasGroupCount<T>::value, bool> = true>
+std::set<CpuIndex> readCacheMembers(const T* info, Pred&& is_cpu_allowed) {
+    std::set<CpuIndex> cpus;
+    // On Windows 10 this will read a 0 because GroupCount doesn't exist
+    int groupCount = std::max(info->Cache.GroupCount, WORD(1));
+    for (WORD procGroup = 0; procGroup < groupCount; ++procGroup)
+    {
+        for (BYTE number = 0; number < WIN_PROCESSOR_GROUP_SIZE; ++number)
+        {
+            WORD           groupNumber = info->Cache.GroupMasks[procGroup].Group;
+            const CpuIndex c = static_cast<CpuIndex>(groupNumber) * WIN_PROCESSOR_GROUP_SIZE
+                             + static_cast<CpuIndex>(number);
+            if (!(info->Cache.GroupMasks[procGroup].Mask & (1ULL << number)) || !is_cpu_allowed(c))
+                continue;
+            cpus.insert(c);
+        }
+    }
+    return cpus;
+}
+
+template<typename T, typename Pred, std::enable_if_t<!HasGroupCount<T>::value, bool> = true>
+std::set<CpuIndex> readCacheMembers(const T* info, Pred&& is_cpu_allowed) {
+    std::set<CpuIndex> cpus;
+    for (BYTE number = 0; number < WIN_PROCESSOR_GROUP_SIZE; ++number)
+    {
+        WORD           groupNumber = info->Cache.GroupMask.Group;
+        const CpuIndex c           = static_cast<CpuIndex>(groupNumber) * WIN_PROCESSOR_GROUP_SIZE
+                         + static_cast<CpuIndex>(number);
+        if (!(info->Cache.GroupMask.Mask & (1ULL << number)) || !is_cpu_allowed(c))
+            continue;
+        cpus.insert(c);
+    }
+    return cpus;
+}
+
 #endif
 
 #if defined(__linux__) && !defined(__ANDROID__)
@@ -447,14 +491,39 @@ class NumaReplicatedAccessToken {
     NumaIndex n;
 };
 
+struct L3Domain {
+    NumaIndex          systemNumaIndex{};
+    std::set<CpuIndex> cpus{};
+};
+
+// Use system NUMA nodes
+struct SystemNumaPolicy {};
+// Use system-reported L3 domains
+struct L3DomainsPolicy {};
+// Group system-reported L3 domains until they reach bundleSize
+struct BundledL3Policy {
+    size_t bundleSize;
+};
+
+using NumaAutoPolicy = std::variant<SystemNumaPolicy, L3DomainsPolicy, BundledL3Policy>;
+
 // Designed as immutable, because there is no good reason to alter an already
 // existing config in a way that doesn't require recreating it completely, and
 // it would be complex and expensive to maintain class invariants.
 // The CPU (processor) numbers always correspond to the actual numbering used
 // by the system. The NUMA node numbers MAY NOT correspond to the system's
-// numbering of the NUMA nodes. In particular, empty nodes may be removed, or
-// the user may create custom nodes. It is guaranteed that NUMA nodes are NOT
-// empty: every node exposed by NumaConfig has at least one processor assigned.
+// numbering of the NUMA nodes. In particular, by default, if the processor has
+// non-uniform cache access within a NUMA node (i.e., a non-unified L3 cache structure),
+// then L3 domains within a system NUMA node will be used to subdivide it
+// into multiple logical NUMA nodes in the config. Additionally, empty nodes may
+// be removed, or the user may create custom nodes.
+//
+// As a special case, when performing system-wide replication of read-only data
+// (i.e., LazyNumaReplicatedSystemWide), the system NUMA node is used, rather than
+// custom or L3-aware nodes. See that class's get_discriminator() function.
+//
+// It is guaranteed that NUMA nodes are NOT empty: every node exposed by NumaConfig
+// has at least one processor assigned.
 //
 // We use startup affinities so as not to modify its own behaviour in time.
 //
@@ -469,78 +538,19 @@ class NumaConfig {
         add_cpu_range_to_node(NumaIndex{0}, CpuIndex{0}, numCpus - 1);
     }
 
-    // This function queries the system for the mapping of processors to NUMA nodes.
-    // On Linux we read from standardized kernel sysfs, with a fallback to single NUMA
-    // node. On Windows we utilize GetNumaProcessorNodeEx, which has its quirks, see
-    // comment for Windows implementation of get_process_affinity.
-    static NumaConfig from_system([[maybe_unused]] bool respectProcessAffinity = true) {
+    // This function gets a NumaConfig based on the system's provided information.
+    // The available policies are documented above.
+    static NumaConfig from_system([[maybe_unused]] const NumaAutoPolicy& policy,
+                                  bool respectProcessAffinity = true) {
         NumaConfig cfg = empty();
 
-#if defined(__linux__) && !defined(__ANDROID__)
+#if !((defined(__linux__) && !defined(__ANDROID__)) || defined(_WIN64))
+        // Fallback for unsupported systems.
+        for (CpuIndex c = 0; c < SYSTEM_THREADS_NB; ++c)
+            cfg.add_cpu_to_node(NumaIndex{0}, c);
+#else
 
-        std::set<CpuIndex> allowedCpus;
-
-        if (respectProcessAffinity)
-            allowedCpus = STARTUP_PROCESSOR_AFFINITY;
-
-        auto is_cpu_allowed = [respectProcessAffinity, &allowedCpus](CpuIndex c) {
-            return !respectProcessAffinity || allowedCpus.count(c) == 1;
-        };
-
-        // On Linux things are straightforward, since there's no processor groups and
-        // any thread can be scheduled on all processors.
-        // We try to gather this information from the sysfs first
-        // https://www.kernel.org/doc/Documentation/ABI/stable/sysfs-devices-node
-
-        bool useFallback = false;
-        auto fallback    = [&]() {
-            useFallback = true;
-            cfg         = empty();
-        };
-
-        // /sys/devices/system/node/online contains information about active NUMA nodes
-        auto nodeIdsStr = read_file_to_string("/sys/devices/system/node/online");
-        if (!nodeIdsStr.has_value() || nodeIdsStr->empty())
-        {
-            fallback();
-        }
-        else
-        {
-            remove_whitespace(*nodeIdsStr);
-            for (size_t n : indices_from_shortened_string(*nodeIdsStr))
-            {
-                // /sys/devices/system/node/node.../cpulist
-                std::string path =
-                  std::string("/sys/devices/system/node/node") + std::to_string(n) + "/cpulist";
-                auto cpuIdsStr = read_file_to_string(path);
-                // Now, we only bail if the file does not exist. Some nodes may be
-                // empty, that's fine. An empty node still has a file that appears
-                // to have some whitespace, so we need to handle that.
-                if (!cpuIdsStr.has_value())
-                {
-                    fallback();
-                    break;
-                }
-                else
-                {
-                    remove_whitespace(*cpuIdsStr);
-                    for (size_t c : indices_from_shortened_string(*cpuIdsStr))
-                    {
-                        if (is_cpu_allowed(c))
-                            cfg.add_cpu_to_node(n, c);
-                    }
-                }
-            }
-        }
-
-        if (useFallback)
-        {
-            for (CpuIndex c = 0; c < SYSTEM_THREADS_NB; ++c)
-                if (is_cpu_allowed(c))
-                    cfg.add_cpu_to_node(NumaIndex{0}, c);
-        }
-
-#elif defined(_WIN64)
+    #if defined(_WIN64)
 
         std::optional<std::set<CpuIndex>> allowedCpus;
 
@@ -555,28 +565,38 @@ class NumaConfig {
             return !allowedCpus.has_value() || allowedCpus->count(c) == 1;
         };
 
-        WORD numProcGroups = GetActiveProcessorGroupCount();
-        for (WORD procGroup = 0; procGroup < numProcGroups; ++procGroup)
-        {
-            for (BYTE number = 0; number < WIN_PROCESSOR_GROUP_SIZE; ++number)
-            {
-                PROCESSOR_NUMBER procnum;
-                procnum.Group    = procGroup;
-                procnum.Number   = number;
-                procnum.Reserved = 0;
-                USHORT nodeNumber;
+    #elif defined(__linux__) && !defined(__ANDROID__)
 
-                const BOOL     status = GetNumaProcessorNodeEx(&procnum, &nodeNumber);
-                const CpuIndex c      = static_cast<CpuIndex>(procGroup) * WIN_PROCESSOR_GROUP_SIZE
-                                 + static_cast<CpuIndex>(number);
-                if (status != 0 && nodeNumber != std::numeric_limits<USHORT>::max()
-                    && is_cpu_allowed(c))
-                {
-                    cfg.add_cpu_to_node(nodeNumber, c);
-                }
+        std::set<CpuIndex> allowedCpus;
+
+        if (respectProcessAffinity)
+            allowedCpus = STARTUP_PROCESSOR_AFFINITY;
+
+        auto is_cpu_allowed = [respectProcessAffinity, &allowedCpus](CpuIndex c) {
+            return !respectProcessAffinity || allowedCpus.count(c) == 1;
+        };
+
+    #endif
+
+        bool l3Success = false;
+        if (!std::holds_alternative<SystemNumaPolicy>(policy))
+        {
+            size_t l3BundleSize = 0;
+            if (const auto* v = std::get_if<BundledL3Policy>(&policy))
+            {
+                l3BundleSize = v->bundleSize;
+            }
+            if (auto l3Cfg =
+                  try_get_l3_aware_config(respectProcessAffinity, l3BundleSize, is_cpu_allowed))
+            {
+                cfg       = std::move(*l3Cfg);
+                l3Success = true;
             }
         }
+        if (!l3Success)
+            cfg = from_system_numa(respectProcessAffinity, is_cpu_allowed);
 
+    #if defined(_WIN64)
         // Split the NUMA nodes to be contained within a group if necessary.
         // This is needed between Windows 10 Build 20348 and Windows 11, because
         // the new NUMA allocation behaviour was introduced while there was
@@ -623,12 +643,7 @@ class NumaConfig {
 
             cfg = std::move(splitCfg);
         }
-
-#else
-
-        // Fallback for unsupported systems.
-        for (CpuIndex c = 0; c < SYSTEM_THREADS_NB; ++c)
-            cfg.add_cpu_to_node(NumaIndex{0}, c);
+    #endif
 
 #endif
 
@@ -1041,6 +1056,227 @@ class NumaConfig {
 
         return indices;
     }
+
+    // This function queries the system for the mapping of processors to NUMA nodes.
+    // On Linux we read from standardized kernel sysfs, with a fallback to single NUMA
+    // node. On Windows we utilize GetNumaProcessorNodeEx, which has its quirks, see
+    // comment for Windows implementation of get_process_affinity.
+    template<typename Pred>
+    static NumaConfig from_system_numa([[maybe_unused]] bool   respectProcessAffinity,
+                                       [[maybe_unused]] Pred&& is_cpu_allowed) {
+        NumaConfig cfg = empty();
+
+#if defined(__linux__) && !defined(__ANDROID__)
+
+        // On Linux things are straightforward, since there's no processor groups and
+        // any thread can be scheduled on all processors.
+        // We try to gather this information from the sysfs first
+        // https://www.kernel.org/doc/Documentation/ABI/stable/sysfs-devices-node
+
+        bool useFallback = false;
+        auto fallback    = [&]() {
+            useFallback = true;
+            cfg         = empty();
+        };
+
+        // /sys/devices/system/node/online contains information about active NUMA nodes
+        auto nodeIdsStr = read_file_to_string("/sys/devices/system/node/online");
+        if (!nodeIdsStr.has_value() || nodeIdsStr->empty())
+        {
+            fallback();
+        }
+        else
+        {
+            remove_whitespace(*nodeIdsStr);
+            for (size_t n : indices_from_shortened_string(*nodeIdsStr))
+            {
+                // /sys/devices/system/node/node.../cpulist
+                std::string path =
+                  std::string("/sys/devices/system/node/node") + std::to_string(n) + "/cpulist";
+                auto cpuIdsStr = read_file_to_string(path);
+                // Now, we only bail if the file does not exist. Some nodes may be
+                // empty, that's fine. An empty node still has a file that appears
+                // to have some whitespace, so we need to handle that.
+                if (!cpuIdsStr.has_value())
+                {
+                    fallback();
+                    break;
+                }
+                else
+                {
+                    remove_whitespace(*cpuIdsStr);
+                    for (size_t c : indices_from_shortened_string(*cpuIdsStr))
+                    {
+                        if (is_cpu_allowed(c))
+                            cfg.add_cpu_to_node(n, c);
+                    }
+                }
+            }
+        }
+
+        if (useFallback)
+        {
+            for (CpuIndex c = 0; c < SYSTEM_THREADS_NB; ++c)
+                if (is_cpu_allowed(c))
+                    cfg.add_cpu_to_node(NumaIndex{0}, c);
+        }
+
+#elif defined(_WIN64)
+
+        WORD numProcGroups = GetActiveProcessorGroupCount();
+        for (WORD procGroup = 0; procGroup < numProcGroups; ++procGroup)
+        {
+            for (BYTE number = 0; number < WIN_PROCESSOR_GROUP_SIZE; ++number)
+            {
+                PROCESSOR_NUMBER procnum;
+                procnum.Group    = procGroup;
+                procnum.Number   = number;
+                procnum.Reserved = 0;
+                USHORT nodeNumber;
+
+                const BOOL     status = GetNumaProcessorNodeEx(&procnum, &nodeNumber);
+                const CpuIndex c      = static_cast<CpuIndex>(procGroup) * WIN_PROCESSOR_GROUP_SIZE
+                                 + static_cast<CpuIndex>(number);
+                if (status != 0 && nodeNumber != std::numeric_limits<USHORT>::max()
+                    && is_cpu_allowed(c))
+                {
+                    cfg.add_cpu_to_node(nodeNumber, c);
+                }
+            }
+        }
+
+#else
+
+        abort();  // should not reach here
+
+#endif
+
+        return cfg;
+    }
+
+    template<typename Pred>
+    static std::optional<NumaConfig> try_get_l3_aware_config(
+      bool respectProcessAffinity, size_t bundleSize, [[maybe_unused]] Pred&& is_cpu_allowed) {
+        // Get the normal system configuration so we know to which NUMA node
+        // each L3 domain belongs.
+        NumaConfig systemConfig =
+          NumaConfig::from_system(SystemNumaPolicy{}, respectProcessAffinity);
+        std::vector<L3Domain> l3Domains;
+
+#if defined(__linux__) && !defined(__ANDROID__)
+
+        std::set<CpuIndex> seenCpus;
+        auto               nextUnseenCpu = [&seenCpus]() {
+            for (CpuIndex i = 0;; ++i)
+                if (!seenCpus.count(i))
+                    return i;
+        };
+
+        while (true)
+        {
+            CpuIndex next = nextUnseenCpu();
+            auto     siblingsStr =
+              read_file_to_string("/sys/devices/system/cpu/cpu" + std::to_string(next)
+                                  + "/cache/index3/shared_cpu_list");
+
+            if (!siblingsStr.has_value() || siblingsStr->empty())
+            {
+                break;  // we have read all available CPUs
+            }
+
+            L3Domain domain;
+            for (size_t c : indices_from_shortened_string(*siblingsStr))
+            {
+                if (is_cpu_allowed(c))
+                {
+                    domain.systemNumaIndex = systemConfig.nodeByCpu.at(c);
+                    domain.cpus.insert(c);
+                }
+                seenCpus.insert(c);
+            }
+            if (!domain.cpus.empty())
+            {
+                l3Domains.emplace_back(std::move(domain));
+            }
+        }
+
+#elif defined(_WIN64)
+
+        DWORD bufSize = 0;
+        GetLogicalProcessorInformationEx(RelationCache, nullptr, &bufSize);
+        if (GetLastError() != ERROR_INSUFFICIENT_BUFFER)
+            return std::nullopt;
+
+        std::vector<char> buffer(bufSize);
+        auto info = reinterpret_cast<PSYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX>(buffer.data());
+        if (!GetLogicalProcessorInformationEx(RelationCache, info, &bufSize))
+            return std::nullopt;
+
+        while (reinterpret_cast<char*>(info) < buffer.data() + bufSize)
+        {
+            info = std::launder(info);
+            if (info->Relationship == RelationCache && info->Cache.Level == 3)
+            {
+                L3Domain domain{};
+                domain.cpus = readCacheMembers(info, is_cpu_allowed);
+                if (!domain.cpus.empty())
+                {
+                    domain.systemNumaIndex = systemConfig.nodeByCpu.at(*domain.cpus.begin());
+                    l3Domains.push_back(std::move(domain));
+                }
+            }
+            // Variable length data structure, advance to next
+            info = reinterpret_cast<PSYSTEM_LOGICAL_PROCESSOR_INFORMATION_EX>(
+              reinterpret_cast<char*>(info) + info->Size);
+        }
+#endif
+
+        if (!l3Domains.empty())
+            return {NumaConfig::from_l3_info(std::move(l3Domains), bundleSize)};
+
+        return std::nullopt;
+    }
+
+
+    static NumaConfig from_l3_info(std::vector<L3Domain>&& domains, size_t bundleSize) {
+        assert(!domains.empty());
+
+        std::map<NumaIndex, std::vector<L3Domain>> list;
+        for (auto& d : domains)
+            list[d.systemNumaIndex].emplace_back(std::move(d));
+
+        NumaConfig cfg = empty();
+        NumaIndex  n   = 0;
+        for (auto& [_, ds] : list)
+        {
+            bool changed;
+            // Scan through pairs and merge them. With roughly equal L3 sizes, should give
+            // a decent distribution.
+            do
+            {
+                changed = false;
+                for (size_t j = 0; j + 1 < ds.size(); ++j)
+                {
+                    if (ds[j].cpus.size() + ds[j + 1].cpus.size() <= bundleSize)
+                    {
+                        changed = true;
+                        ds[j].cpus.merge(ds[j + 1].cpus);
+                        ds.erase(ds.begin() + j + 1);
+                    }
+                }
+                // ds.size() has decreased if changed is true, so this loop will terminate
+            } while (changed);
+            for (const L3Domain& d : ds)
+            {
+                const NumaIndex dn = n++;
+                for (CpuIndex cpu : d.cpus)
+                {
+                    cfg.add_cpu_to_node(dn, cpu);
+                }
+            }
+        }
+        return cfg;
+    }
 };
 
 class NumaReplicationContext;
@@ -1345,12 +1581,12 @@ class LazyNumaReplicatedSystemWide: public NumaReplicatedBase {
 
     std::size_t get_discriminator(NumaIndex idx) const {
         const NumaConfig& cfg     = get_numa_config();
-        const NumaConfig& cfg_sys = NumaConfig::from_system(false);
+        const NumaConfig& cfg_sys = NumaConfig::from_system(SystemNumaPolicy{}, false);
         // as a discriminator, locate the hardware/system numadomain this cpuindex belongs to
         CpuIndex    cpu     = *cfg.nodes[idx].begin();  // get a CpuIndex from NumaIndex
         NumaIndex   sys_idx = cfg_sys.is_cpu_assigned(cpu) ? cfg_sys.nodeByCpu.at(cpu) : 0;
         std::string s       = cfg_sys.to_string() + "$" + std::to_string(sys_idx);
-        return std::hash<std::string>{}(s);
+        return static_cast<std::size_t>(hash_string(s));
     }
 
     void ensure_present(NumaIndex idx) const {

src/position.cpp

@@ -66,12 +66,15 @@ std::ostream& operator<<(std::ostream& os, const Position& pos) {
 
     os << "\n +---+---+---+---+---+---+---+---+\n";
 
-    for (Rank r = RANK_8; r >= RANK_1; --r)
+    for (Rank r = RANK_8;; --r)
     {
         for (File f = FILE_A; f <= FILE_H; ++f)
             os << " | " << PieceToChar[pos.piece_on(make_square(f, r))];
 
         os << " | " << (1 + r) << "\n +---+---+---+---+---+---+---+---+\n";
+
+        if (r == RANK_1)
+            break;
     }
 
     os << "   a   b   c   d   e   f   g   h\n"
@@ -416,7 +419,7 @@ string Position::fen() const {
     int                emptyCnt;
     std::ostringstream ss;
 
-    for (Rank r = RANK_8; r >= RANK_1; --r)
+    for (Rank r = RANK_8;; --r)
     {
         for (File f = FILE_A; f <= FILE_H; ++f)
         {
@@ -430,8 +433,9 @@ string Position::fen() const {
                 ss << PieceToChar[piece_on(make_square(f, r))];
         }
 
-        if (r > RANK_1)
-            ss << '/';
+        if (r == RANK_1)
+            break;
+        ss << '/';
     }
 
     ss << (sideToMove == WHITE ? " w " : " b ");
@@ -1477,10 +1481,13 @@ void Position::flip() {
     string            f, token;
     std::stringstream ss(fen());
 
-    for (Rank r = RANK_8; r >= RANK_1; --r)  // Piece placement
+    for (Rank r = RANK_8;; --r)  // Piece placement
     {
         std::getline(ss, token, r > RANK_1 ? '/' : ' ');
         f.insert(0, token + (f.empty() ? " " : "/"));
+
+        if (r == RANK_1)
+            break;
     }
 
     ss >> token;                        // Active color

src/search.cpp

@@ -1206,8 +1206,7 @@ moves_loop:  // When in check, search starts here
 
         // Increase reduction if next ply has a lot of fail high
         if ((ss + 1)->cutoffCnt > 1)
-            r += 120 + 1024 * ((ss + 1)->cutoffCnt > 2) + 100 * ((ss + 1)->cutoffCnt > 3)
-               + 1024 * allNode;
+            r += 256 + 1024 * ((ss + 1)->cutoffCnt > 2) + 1024 * allNode;
 
         // For first picked move (ttMove) reduce reduction
         if (move == ttData.move)
@@ -1433,6 +1432,7 @@ moves_loop:  // When in check, search starts here
 
         bonusScale = std::max(bonusScale, 0);
 
+        // scaledBonus ranges from 0 to roughly 2.3M, overflows happen for multipliers larger than 900
         const int scaledBonus = std::min(141 * depth - 87, 1351) * bonusScale;
 
         update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
@@ -1441,8 +1441,7 @@ moves_loop:  // When in check, search starts here
         mainHistory[~us][((ss - 1)->currentMove).raw()] << scaledBonus * 243 / 32768;
 
         if (type_of(pos.piece_on(prevSq)) != PAWN && ((ss - 1)->currentMove).type_of() != PROMOTION)
-            sharedHistory.pawn_entry(pos)[pos.piece_on(prevSq)][prevSq]
-              << scaledBonus * 1160 / 32768;
+            sharedHistory.pawn_entry(pos)[pos.piece_on(prevSq)][prevSq] << scaledBonus * 290 / 8192;
     }
 
     // Bonus for prior capture countermove that caused the fail low
@@ -1653,7 +1652,7 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta)
                 // we can prune this move.
                 if (!pos.see_ge(move, alpha - futilityBase))
                 {
-                    bestValue = std::min(alpha, futilityBase);
+                    bestValue = std::max(bestValue, std::min(alpha, futilityBase));
                     continue;
                 }
             }

src/shm.h

@@ -20,6 +20,7 @@
 #define SHM_H_INCLUDED
 
 #include <algorithm>
+#include <cinttypes>
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
@@ -35,7 +36,7 @@
 #include <utility>
 #include <variant>
 
-#if !defined(_WIN32) && !defined(__ANDROID__)
+#if defined(__linux__) && !defined(__ANDROID__)
     #include "shm_linux.h"
 #endif
 
@@ -59,7 +60,7 @@
         #define NOMINMAX
     #endif
     #include <windows.h>
-#else
+#elif defined(__linux__)
     #include <cstring>
     #include <fcntl.h>
     #include <pthread.h>
@@ -406,7 +407,7 @@ class SharedMemoryBackend {
     std::string last_error_message;
 };
 
-#elif !defined(__ANDROID__)
+#elif defined(__linux__) && !defined(__ANDROID__)
 
 template<typename T>
 class SharedMemoryBackend {
@@ -512,12 +513,9 @@ template<typename T>
 struct SystemWideSharedConstant {
    private:
     static std::string createHashString(const std::string& input) {
-        size_t hash = std::hash<std::string>{}(input);
-
-        std::stringstream ss;
-        ss << std::hex << std::setfill('0') << hash;
-
-        return ss.str();
+        char buf[1024];
+        std::snprintf(buf, sizeof(buf), "%016" PRIx64, hash_string(input));
+        return buf;
     }
 
    public:
@@ -534,13 +532,13 @@ struct SystemWideSharedConstant {
     // that are not present in the content, for example NUMA node allocation.
     SystemWideSharedConstant(const T& value, std::size_t discriminator = 0) {
         std::size_t content_hash    = std::hash<T>{}(value);
-        std::size_t executable_hash = std::hash<std::string>{}(getExecutablePathHash());
+        std::size_t executable_hash = hash_string(getExecutablePathHash());
 
-        std::string shm_name = std::string("Local\\sf_") + std::to_string(content_hash) + "$"
-                             + std::to_string(executable_hash) + "$"
-                             + std::to_string(discriminator);
+        char buf[1024];
+        std::snprintf(buf, sizeof(buf), "Local\\sf_%zu$%zu$%zu", content_hash, executable_hash, discriminator);
+        std::string shm_name = buf;
 
-#if !defined(_WIN32)
+#if defined(__linux__) && !defined(__ANDROID__)
         // POSIX shared memory names must start with a slash
         shm_name = "/sf_" + createHashString(shm_name);
 

src/shm_linux.h

@@ -19,6 +19,10 @@
 #ifndef SHM_LINUX_H_INCLUDED
 #define SHM_LINUX_H_INCLUDED
 
+#if !defined(__linux__) || defined(__ANDROID__)
+#error shm_linux.h should not be included on this platform.
+#endif
+
 #include <atomic>
 #include <cassert>
 #include <cerrno>
@@ -33,7 +37,6 @@
 #include <string>
 #include <inttypes.h>
 #include <type_traits>
-#include <unordered_set>
 
 #include <fcntl.h>
 #include <signal.h>
@@ -41,16 +44,10 @@
 #include <sys/mman.h>
 #include <sys/stat.h>
 #include <unistd.h>
+#include <limits.h>
+#define SF_MAX_SEM_NAME_LEN NAME_MAX
 
-#if defined(__NetBSD__) || defined(__DragonFly__) || defined(__linux__)
-    #include <limits.h>
-    #define SF_MAX_SEM_NAME_LEN NAME_MAX
-#elif defined(__APPLE__)
-    #define SF_MAX_SEM_NAME_LEN 31
-#else
-    #define SF_MAX_SEM_NAME_LEN 255
-#endif
-
+#include "misc.h"
 
 namespace Stockfish::shm {
 
@@ -67,48 +64,60 @@ struct ShmHeader {
 class SharedMemoryBase {
    public:
     virtual ~SharedMemoryBase()                      = default;
-    virtual void               close() noexcept      = 0;
+    virtual void               close(bool skip_unmap = false) noexcept      = 0;
     virtual const std::string& name() const noexcept = 0;
 };
 
 class SharedMemoryRegistry {
    private:
     static std::mutex                            registry_mutex_;
-    static std::unordered_set<SharedMemoryBase*> active_instances_;
+    static std::vector<SharedMemoryBase*> active_instances_;
 
    public:
     static void register_instance(SharedMemoryBase* instance) {
         std::scoped_lock lock(registry_mutex_);
-        active_instances_.insert(instance);
+        active_instances_.push_back(instance);
     }
 
     static void unregister_instance(SharedMemoryBase* instance) {
         std::scoped_lock lock(registry_mutex_);
-        active_instances_.erase(instance);
+        active_instances_.erase(
+            std::remove(active_instances_.begin(), active_instances_.end(), instance), active_instances_.end());
     }
 
-    static void cleanup_all() noexcept {
+    static void cleanup_all(bool skip_unmap = false) noexcept {
         std::scoped_lock lock(registry_mutex_);
         for (auto* instance : active_instances_)
-            instance->close();
+            instance->close(skip_unmap);
         active_instances_.clear();
     }
 };
 
 inline std::mutex                            SharedMemoryRegistry::registry_mutex_;
-inline std::unordered_set<SharedMemoryBase*> SharedMemoryRegistry::active_instances_;
+inline std::vector<SharedMemoryBase*> SharedMemoryRegistry::active_instances_;
 
 class CleanupHooks {
    private:
     static std::once_flag register_once_;
 
     static void handle_signal(int sig) noexcept {
-        SharedMemoryRegistry::cleanup_all();
-        _Exit(128 + sig);
+        // Search threads may still be running, so skip munmap (but still perform
+        // other cleanup actions). The memory mappings will be released on exit.
+        SharedMemoryRegistry::cleanup_all(true);
+
+        // Invoke the default handler, which will exit
+        struct sigaction sa;
+        sa.sa_handler = SIG_DFL;
+        sigemptyset(&sa.sa_mask);
+        sa.sa_flags = 0;
+        if (sigaction(sig, &sa, nullptr) == -1)
+            _Exit(128 + sig);
+
+        raise(sig);
     }
 
     static void register_signal_handlers() noexcept {
-        std::atexit([]() { SharedMemoryRegistry::cleanup_all(); });
+        std::atexit([]() { SharedMemoryRegistry::cleanup_all(true); });
 
         constexpr int signals[] = {SIGHUP,  SIGINT,  SIGQUIT, SIGILL, SIGABRT, SIGFPE,
                                    SIGSEGV, SIGTERM, SIGBUS,  SIGSYS, SIGXCPU, SIGXFSZ};
@@ -170,9 +179,10 @@ class SharedMemory: public detail::SharedMemoryBase {
     }
 
     static std::string make_sentinel_base(const std::string& name) {
-        uint64_t hash = std::hash<std::string>{}(name);
         char     buf[32];
-        std::snprintf(buf, sizeof(buf), "sfshm_%016" PRIx64, static_cast<uint64_t>(hash));
+        // Using std::to_string here causes non-deterministic PGO builds.
+        // snprintf, being part of libc, is insensitive to the formatted values.
+        std::snprintf(buf, sizeof(buf), "sfshm_%016" PRIu64, hash_string(name));
         return buf;
     }
 
@@ -318,7 +328,7 @@ class SharedMemory: public detail::SharedMemoryBase {
         }
     }
 
-    void close() noexcept override {
+    void close(bool skip_unmap = false) noexcept override {
         if (fd_ == -1 && mapped_ptr_ == nullptr)
             return;
 
@@ -345,7 +355,10 @@ class SharedMemory: public detail::SharedMemoryBase {
             decrement_refcount_relaxed();
         }
 
-        unmap_region();
+        if (skip_unmap)
+            mapped_ptr_ = nullptr;
+        else
+            unmap_region();
 
         if (remove_region)
             shm_unlink(name_.c_str());
@@ -359,7 +372,8 @@ class SharedMemory: public detail::SharedMemoryBase {
             fd_ = -1;
         }
 
-        reset();
+        if (!skip_unmap)
+            reset();
     }
 
     const std::string& name() const noexcept override { return name_; }
@@ -427,11 +441,10 @@ class SharedMemory: public detail::SharedMemoryBase {
     }
 
     std::string sentinel_full_path(pid_t pid) const {
-        std::string path = "/dev/shm/";
-        path += sentinel_base_;
-        path.push_back('.');
-        path += std::to_string(pid);
-        return path;
+        char buf[1024];
+        // See above snprintf comment
+        std::snprintf(buf, sizeof(buf), "/dev/shm/%s.%ld", sentinel_base_.c_str(), long(pid));
+        return buf;
     }
 
     void decrement_refcount_relaxed() noexcept {

src/syzygy/tbprobe.cpp

@@ -709,15 +709,11 @@ int map_score(TBTable<DTZ>* entry, File f, int value, WDLScore wdl) {
     return value + 1;
 }
 
-// A temporary fix for the compiler bug with AVX-512. (#4450)
-#ifdef USE_AVX512
-    #if defined(__clang__) && defined(__clang_major__) && __clang_major__ >= 15
-        #define CLANG_AVX512_BUG_FIX __attribute__((optnone))
-    #endif
-#endif
-
-#ifndef CLANG_AVX512_BUG_FIX
-    #define CLANG_AVX512_BUG_FIX
+// A temporary fix for the compiler bug with vectorization. (#4450)
+#if defined(__clang__) && defined(__clang_major__) && __clang_major__ >= 15
+    #define DISABLE_CLANG_LOOP_VEC _Pragma("clang loop vectorize(disable)")
+#else
+    #define DISABLE_CLANG_LOOP_VEC
 #endif
 
 // Compute a unique index out of a position and use it to probe the TB file. To
@@ -727,8 +723,7 @@ int map_score(TBTable<DTZ>* entry, File f, int value, WDLScore wdl) {
 //      idx = Binomial[1][s1] + Binomial[2][s2] + ... + Binomial[k][sk]
 //
 template<typename T, typename Ret = typename T::Ret>
-CLANG_AVX512_BUG_FIX Ret
-do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* result) {
+Ret do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* result) {
 
     Square     squares[TBPIECES];
     Piece      pieces[TBPIECES];
@@ -812,8 +807,11 @@ do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* result)
     // Now we map again the squares so that the square of the lead piece is in
     // the triangle A1-D1-D4.
     if (file_of(squares[0]) > FILE_D)
+    {
+        DISABLE_CLANG_LOOP_VEC
         for (int i = 0; i < size; ++i)
             squares[i] = flip_file(squares[i]);
+    }
 
     // Encode leading pawns starting with the one with minimum MapPawns[] and
     // proceeding in ascending order.
@@ -832,19 +830,26 @@ do_probe_table(const Position& pos, T* entry, WDLScore wdl, ProbeState* result)
     // In positions without pawns, we further flip the squares to ensure leading
     // piece is below RANK_5.
     if (rank_of(squares[0]) > RANK_4)
+    {
+        DISABLE_CLANG_LOOP_VEC
         for (int i = 0; i < size; ++i)
             squares[i] = flip_rank(squares[i]);
+    }
 
     // Look for the first piece of the leading group not on the A1-D4 diagonal
     // and ensure it is mapped below the diagonal.
+    DISABLE_CLANG_LOOP_VEC
     for (int i = 0; i < d->groupLen[0]; ++i)
     {
         if (!off_A1H8(squares[i]))
             continue;
 
         if (off_A1H8(squares[i]) > 0)  // A1-H8 diagonal flip: SQ_A3 -> SQ_C1
+        {
+            DISABLE_CLANG_LOOP_VEC
             for (int j = i; j < size; ++j)
                 squares[j] = Square(((squares[j] >> 3) | (squares[j] << 3)) & 63);
+        }
         break;
     }
 

src/thread.cpp

@@ -213,22 +213,31 @@ void ThreadPool::set(const NumaConfig&                           numaConfig,
 
         while (threads.size() < requested)
         {
-            const size_t    threadId = threads.size();
-            const NumaIndex numaId   = doBindThreads ? boundThreadToNumaNode[threadId] : 0;
-            auto            manager  = threadId == 0 ? std::unique_ptr<Search::ISearchManager>(
-                                             std::make_unique<Search::SearchManager>(updateContext))
-                                                     : std::make_unique<Search::NullSearchManager>();
+            const size_t    threadId      = threads.size();
+            const NumaIndex numaId        = doBindThreads ? boundThreadToNumaNode[threadId] : 0;
+            auto            create_thread = [&]() {
+                auto manager = threadId == 0
+                                          ? std::unique_ptr<Search::ISearchManager>(
+                                   std::make_unique<Search::SearchManager>(updateContext))
+                                          : std::make_unique<Search::NullSearchManager>();
 
-            // When not binding threads we want to force all access to happen
-            // from the same NUMA node, because in case of NUMA replicated memory
-            // accesses we don't want to trash cache in case the threads get scheduled
-            // on the same NUMA node.
-            auto binder = doBindThreads ? OptionalThreadToNumaNodeBinder(numaConfig, numaId)
-                                        : OptionalThreadToNumaNodeBinder(numaId);
+                // When not binding threads we want to force all access to happen
+                // from the same NUMA node, because in case of NUMA replicated memory
+                // accesses we don't want to trash cache in case the threads get scheduled
+                // on the same NUMA node.
+                auto binder = doBindThreads ? OptionalThreadToNumaNodeBinder(numaConfig, numaId)
+                                                       : OptionalThreadToNumaNodeBinder(numaId);
 
-            threads.emplace_back(std::make_unique<Thread>(sharedState, std::move(manager), threadId,
-                                                          counts[numaId]++, threadsPerNode[numaId],
-                                                          binder));
+                threads.emplace_back(std::make_unique<Thread>(sharedState, std::move(manager),
+                                                                         threadId, counts[numaId]++,
+                                                                         threadsPerNode[numaId], binder));
+            };
+
+            // Ensure the worker thread inherits the intended NUMA affinity at creation.
+            if (doBindThreads)
+                numaConfig.execute_on_numa_node(numaId, create_thread);
+            else
+                create_thread();
         }
 
         clear();

src/timeman.h

@@ -26,7 +26,7 @@
 namespace Stockfish {
 
 class OptionsMap;
-enum Color : int8_t;
+enum Color : uint8_t;
 
 namespace Search {
 struct LimitsType;

src/types.h

@@ -117,13 +117,13 @@ using Bitboard = uint64_t;
 constexpr int MAX_MOVES = 256;
 constexpr int MAX_PLY   = 246;
 
-enum Color : int8_t {
+enum Color : uint8_t {
     WHITE,
     BLACK,
     COLOR_NB = 2
 };
 
-enum CastlingRights : int8_t {
+enum CastlingRights : uint8_t {
     NO_CASTLING,
     WHITE_OO,
     WHITE_OOO = WHITE_OO << 1,
@@ -139,7 +139,7 @@ enum CastlingRights : int8_t {
     CASTLING_RIGHT_NB = 16
 };
 
-enum Bound : int8_t {
+enum Bound : uint8_t {
     BOUND_NONE,
     BOUND_UPPER,
     BOUND_LOWER,
@@ -190,13 +190,13 @@ constexpr Value QueenValue  = 2538;
 
 
 // clang-format off
-enum PieceType : std::int8_t {
+enum PieceType : std::uint8_t {
     NO_PIECE_TYPE, PAWN, KNIGHT, BISHOP, ROOK, QUEEN, KING,
     ALL_PIECES = 0,
     PIECE_TYPE_NB = 8
 };
 
-enum Piece : std::int8_t {
+enum Piece : std::uint8_t {
     NO_PIECE,
     W_PAWN = PAWN,     W_KNIGHT, W_BISHOP, W_ROOK, W_QUEEN, W_KING,
     B_PAWN = PAWN + 8, B_KNIGHT, B_BISHOP, B_ROOK, B_QUEEN, B_KING,
@@ -227,7 +227,7 @@ constexpr Depth DEPTH_UNSEARCHED   = -2;
 constexpr Depth DEPTH_ENTRY_OFFSET = -3;
 
 // clang-format off
-enum Square : int8_t {
+enum Square : uint8_t {
     SQ_A1, SQ_B1, SQ_C1, SQ_D1, SQ_E1, SQ_F1, SQ_G1, SQ_H1,
     SQ_A2, SQ_B2, SQ_C2, SQ_D2, SQ_E2, SQ_F2, SQ_G2, SQ_H2,
     SQ_A3, SQ_B3, SQ_C3, SQ_D3, SQ_E3, SQ_F3, SQ_G3, SQ_H3,
@@ -255,7 +255,7 @@ enum Direction : int8_t {
     NORTH_WEST = NORTH + WEST
 };
 
-enum File : int8_t {
+enum File : uint8_t {
     FILE_A,
     FILE_B,
     FILE_C,
@@ -267,7 +267,7 @@ enum File : int8_t {
     FILE_NB
 };
 
-enum Rank : int8_t {
+enum Rank : uint8_t {
     RANK_1,
     RANK_2,
     RANK_3,
@@ -406,7 +406,7 @@ constexpr Key make_key(uint64_t seed) {
 }
 
 
-enum MoveType {
+enum MoveType : uint16_t {
     NORMAL,
     PROMOTION  = 1 << 14,
     EN_PASSANT = 2 << 14,

src/uci.cpp

@@ -507,8 +507,8 @@ WinRateParams win_rate_params(const Position& pos) {
     double m = std::clamp(material, 17, 78) / 58.0;
 
     // Return a = p_a(material) and b = p_b(material), see github.com/official-stockfish/WDL_model
-    constexpr double as[] = {-13.50030198, 40.92780883, -36.82753545, 386.83004070};
-    constexpr double bs[] = {96.53354896, -165.79058388, 90.89679019, 49.29561889};
+    constexpr double as[] = {-72.32565836, 185.93832038, -144.58862193, 416.44950446};
+    constexpr double bs[] = {83.86794042, -136.06112997, 69.98820887, 47.62901433};
 
     double a = (((as[0] * m + as[1]) * m + as[2]) * m) + as[3];
     double b = (((bs[0] * m + bs[1]) * m + bs[2]) * m) + bs[3];

src/uci.h

@@ -33,7 +33,7 @@ namespace Stockfish {
 class Position;
 class Move;
 class Score;
-enum Square : int8_t;
+enum Square : uint8_t;
 using Value = int;
 
 class UCIEngine {