adding zobrist hashing

7 files changed, 611 insertions, 55 deletions

diff --git a/scripts/tests/zobrist.bash b/scripts/tests/zobrist.bash
new file mode 100755
index 0000000..7545f6d
--- /dev/null
+++ b/scripts/tests/zobrist.bash
@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+
+status=0
+
+testZobrist() {
+    local name="$1"
+    local fen="$2"
+    local moves="$3"
+    local expected="$4"
+
+    echo ""
+
+    result=$(./build/mono zobrist "$fen" $moves)
+    if [ "$result" = "$expected" ]; then
+        echo "PASS: $name"
+    else
+        echo "FAIL: $name"
+        echo "  Expected: $expected"
+        echo "  Got:      $result"
+        status=1
+    fi
+}
+
+configs=(
+    # starting position
+    "startpos|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1||5060803636482931868"
+    # single moves
+    "1.d4|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|d2d4|9443689642921087454"
+    "1.e4|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|e2e4|9384546495678726550"
+    "1.c4|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|c2c4|14562399549841627035"
+    # two moves
+    "1.e4 e5|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|e2e4 e7e5|595762792459712928"
+    "1.e4 c5|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|e2e4 c7c5|7227515431820872427"
+    "1.e4 e6|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|e2e4 e7e6|17603279437685838276"
+    "1.e4 c6|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|e2e4 c7c6|1172755318016414253"
+    "1.d4 d5|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|d2d4 d7d5|460664201775194104"
+    # three moves
+    "1.e4 e5 2.Nf3|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|e2e4 e7e5 g1f3|15213300192948443293"
+    "1.d4 d5 2.c4|rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1|d2d4 d7d5 c2c4|9963937660605248767"
+    # different starting FEN
+    "Kiwipete|r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - 0 1||14109232545397825053"
+)
+
+for config in "${configs[@]}"; do
+    IFS='|' read -r name fen moves expected <<< "$config"
+    testZobrist "$name" "$fen" "$moves" "$expected"
+    if [ $status -ne 0 ]; then
+        exit "$status"
+    fi
+done
diff --git a/src/book.cpp b/src/book.cpp
new file mode 100644
index 0000000..e1cd127
--- /dev/null
+++ b/src/book.cpp
@@ -0,0 +1,149 @@
+#include "book.hpp"
+
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <cstdlib>
+#include <fstream>
+#include <iostream>
+#include <random>
+#include <vector>
+
+#include "board/board.hpp"
+
+constexpr int BOOK_DEPTH = 16;
+
+struct BookEntry {
+  uint64_t key;
+  uint16_t move;
+  uint16_t weight;
+  uint32_t learn;
+};
+
+static std::vector<BookEntry> book;
+
+static std::mt19937 rng{std::random_device{}()};
+
+void InitBook(const std::string &path) {
+  std::ifstream file(path, std::ios::binary);
+  if (!file.is_open()) {
+    std::cerr << "info string Could not open book file: " << path << "\n";
+    return;
+  }
+
+  file.seekg(0, std::ios::end);
+  size_t fileSize = static_cast<size_t>(file.tellg());
+  file.seekg(0, std::ios::beg);
+
+  if (fileSize == 0 || fileSize % sizeof(BookEntry) != 0) {
+    std::cerr << "info string Invalid book file size\n";
+    return;
+  }
+
+  size_t numEntries = fileSize / sizeof(BookEntry);
+  book.resize(numEntries);
+  file.read(reinterpret_cast<char *>(book.data()),
+            static_cast<std::streamsize>(fileSize));
+
+  if (!file) {
+    std::cerr << "info string Failed to read book file\n";
+    book.clear();
+    return;
+  }
+
+  // Byteswap if needed (Polyglot books are big-endian)
+  for (auto &entry : book) {
+    uint64_t k = entry.key;
+    entry.key = ((k & 0x00000000000000FFULL) << 56) |
+                ((k & 0x000000000000FF00ULL) << 40) |
+                ((k & 0x0000000000FF0000ULL) << 24) |
+                ((k & 0x00000000FF000000ULL) << 8) |
+                ((k & 0x000000FF00000000ULL) >> 8) |
+                ((k & 0x0000FF0000000000ULL) >> 24) |
+                ((k & 0x00FF000000000000ULL) >> 40) |
+                ((k & 0xFF00000000000000ULL) >> 56);
+
+    uint16_t m = entry.move;
+    entry.move = static_cast<uint16_t>((m >> 8) | (m << 8));
+
+    uint16_t w = entry.weight;
+    entry.weight = static_cast<uint16_t>((w >> 8) | (w << 8));
+
+    uint32_t l = entry.learn;
+    entry.learn = ((l & 0x000000FFU) << 24) | ((l & 0x0000FF00U) << 8) |
+                  ((l & 0x00FF0000U) >> 8) | ((l & 0xFF000000U) >> 24);
+  }
+
+  std::cerr << "info string Book loaded: " << book.size() << " entries\n";
+}
+
+// Convert Polyglot move to Mono internal move format.
+// Polyglot: bits 0-5=to, 6-11=from, 12-14=promo (0=N,1=B,2=R,3=Q)
+// Mono:     bits 0-1=promo (00=N,11=B,01=R,10=Q), 2-7=from, 8-13=to
+static uint16_t PolyglotToMono(uint16_t polyglotMove) {
+  uint8_t to = polyglotMove & 63;
+  uint8_t from = (polyglotMove >> 6) & 63;
+  uint8_t promo = (polyglotMove >> 12) & 7;
+
+  PieceType promotion = NONEPIECE;
+  switch (promo) {
+  case 0:
+    promotion = KNIGHT;
+    break;
+  case 1:
+    promotion = BISHOP;
+    break;
+  case 2:
+    promotion = ROOK;
+    break;
+  case 3:
+    promotion = QUEEN;
+    break;
+  default:
+    break;
+  }
+
+  return CreateMove(from, to, promotion);
+}
+
+uint16_t ProbeBook(uint64_t key) {
+  if (book.empty()) {
+    return 0;
+  }
+
+  // Binary search for first matching entry
+  auto it = std::lower_bound(
+      book.begin(), book.end(), key,
+      [](const BookEntry &a, uint64_t k) { return a.key < k; });
+
+  // Collect all matching entries
+  std::vector<const BookEntry *> matches;
+  while (it != book.end() && it->key == key) {
+    matches.push_back(&(*it));
+    ++it;
+  }
+
+  if (matches.empty()) {
+    return 0;
+  }
+
+  // Weighted random selection
+  int totalWeight = 0;
+  for (const auto *e : matches) {
+    totalWeight += e->weight;
+  }
+
+  std::uniform_int_distribution<int> dist(0, totalWeight - 1);
+  int r = dist(rng);
+
+  for (const auto *e : matches) {
+    r -= e->weight;
+    if (r < 0) {
+      return PolyglotToMono(e->move);
+    }
+  }
+
+  return PolyglotToMono(matches.back()->move);
+}
+
+int GetBookDepth() { return BOOK_DEPTH; }
diff --git a/src/book.hpp b/src/book.hpp
new file mode 100644
index 0000000..4382dc7
--- /dev/null
+++ b/src/book.hpp
@@ -0,0 +1,7 @@
+#pragma once
+#include <cstdint>
+#include <string>
+
+void InitBook(const std::string &path);
+uint16_t ProbeBook(uint64_t key);
+int GetBookDepth();
diff --git a/src/main.cpp b/src/main.cpp
index ade22c9..1fa0701 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -7,12 +7,14 @@
 #include <string>
 
 #include "board/board.hpp"
+#include "board/fen.hpp"
 #include "misc.hpp"
+#include "moves.hpp"
 #include "uci.hpp"
 #include "zobrist.hpp"
 
 static void perft(int argc, char *argv[]) {
-  if (argc != 4 || std::string(argv[1]) != "perft") {
+  if (argc < 4 || std::string(argv[1]) != "perft") {
     std::cout << "Usage: ./mono\n";
     std::cout << "       ./mono perft <non-negative depth> <fen>\n";
     exit(1);
@@ -42,14 +44,37 @@ static void perft(int argc, char *argv[]) {
   std::cout << oss.str() << "\n";
 }
 
+static void zobristCmd(int argc, char *argv[]) {
+  if (argc < 3 || std::string(argv[1]) != "zobrist") {
+    std::cout << "Usage: ./mono zobrist <fen> [moves...]\n";
+    exit(1);
+  }
+
+  std::string fen = argv[2];
+  Game game = initBoard(fen, nullptr);
+
+  for (int i = 3; i < argc; ++i) {
+    uint16_t move = UciToMove(argv[i]);
+    MakeMove(move, &game);
+  }
+
+  uint64_t hash = GenerateZobristKey(&game);
+  std::cout << hash << "\n";
+}
+
 int main(int argc, char *argv[]) {
   InitZobrist();
 
-  if (argc == 4) {
+  if (argc >= 2 && std::string(argv[1]) == "perft") {
     perft(argc, argv);
     return 0;
   }
 
+  if (argc >= 2 && std::string(argv[1]) == "zobrist") {
+    zobristCmd(argc, argv);
+    return 0;
+  }
+
   std::cout << engine_info();
   Uci();
   return 0;
diff --git a/src/uci.cpp b/src/uci.cpp
index 6c035d5..23e8419 100644
--- a/src/uci.cpp
+++ b/src/uci.cpp
@@ -14,6 +14,7 @@
 #include "board/board.hpp"
 #include "board/fen.hpp"
 #include "bot.hpp"
+#include "book.hpp"
 #include "misc.hpp"
 #include "moves.hpp"
 #include "uci.hpp"
@@ -222,13 +223,25 @@ static void GoCommand(Game *game, std::string &cmd) {
     std::cout << "Fatal: Depth must be positive integer";
     exit(1);
   }
-  move_options options = {
-      .wtime = wtime,
-      .btime = btime,
-      .wncr = wncr,
-      .bncr = bncr,
-  };
-  uint16_t best = GetBestMove(game, depth, options);
+
+  // Try opening book first
+  uint16_t bookMove = 0;
+  if (game->MoveClock < GetBookDepth()) {
+    bookMove = ProbeBook(GenerateZobristKey(game));
+  }
+
+  uint16_t best;
+  if (bookMove != 0) {
+    best = bookMove;
+  } else {
+    move_options options = {
+        .wtime = wtime,
+        .btime = btime,
+        .wncr = wncr,
+        .bncr = bncr,
+    };
+    best = GetBestMove(game, depth, options);
+  }
 
   Piece piece = game->pieces[getFromValueFromMove(best)];
 
@@ -309,6 +322,8 @@ void Uci() {
   Game game = initBoard(starting_fen, &transpositions);
   std::string cmd;
 
+  InitBook("book.bin");
+
   while (getline(std::cin, cmd)) {
     if (cmd == "quit") {
       return;
@@ -342,5 +357,9 @@ void Uci() {
     if (cmd == "moves") {
       movesCommnad(&game);
     }
+    if (cmd == "hash") {
+      uint64_t hash = GenerateZobristKey(&game);
+      std::cout << hash << "\n";
+    }
   }
 }
diff --git a/src/zobrist.cpp b/src/zobrist.cpp
index 8c50d3d..5250687 100644
--- a/src/zobrist.cpp
+++ b/src/zobrist.cpp
@@ -1,34 +1,350 @@
 #include "zobrist.hpp"
 #include "board/board.hpp"
-
+#include <cassert>
 #include <cstdint>
-#include <random>
 
-uint64_t PieceKeys[2][7][64];
-uint64_t SideKey;
-uint64_t CastleKeys[16];
-uint64_t EnPassantKeys[8];
+static uint64_t PieceKeys[2][7][64];
+static uint64_t SideKey;
+static uint64_t CastleKeys[4];
+static uint64_t EnPassantKeys[8];
+
+// Polyglot book format random numbers.
+// Layout: [0..767] piece keys (type*2+color)*64+square, [768..771] castling
+// WK/WQ/BK/BQ, [772..779] en passant file a-h, [780] side to move.
+static const uint64_t PolyglotRandom64[781] = {
+    0x9D39247E33776D41, 0x2AF7398005AAA5C7, 0x44DB015024623547,
+    0x9C15F73E62A76AE2, 0x75834465489C0C89, 0x3290AC3A203001BF,
+    0x0FBBAD1F61042279, 0xE83A908FF2FB60CA, 0x0D7E765D58755C10,
+    0x1A083822CEAFE02D, 0x9605D5F0E25EC3B0, 0xD021FF5CD13A2ED5,
+    0x40BDF15D4A672E32, 0x011355146FD56395, 0x5DB4832046F3D9E5,
+    0x239F8B2D7FF719CC, 0x05D1A1AE85B49AA1, 0x679F848F6E8FC971,
+    0x7449BBFF801FED0B, 0x7D11CDB1C3B7ADF0, 0x82C7709E781EB7CC,
+    0xF3218F1C9510786C, 0x331478F3AF51BBE6, 0x4BB38DE5E7219443,
+    0xAA649C6EBCFD50FC, 0x8DBD98A352AFD40B, 0x87D2074B81D79217,
+    0x19F3C751D3E92AE1, 0xB4AB30F062B19ABF, 0x7B0500AC42047AC4,
+    0xC9452CA81A09D85D, 0x24AA6C514DA27500, 0x4C9F34427501B447,
+    0x14A68FD73C910841, 0xA71B9B83461CBD93, 0x03488B95B0F1850F,
+    0x637B2B34FF93C040, 0x09D1BC9A3DD90A94, 0x3575668334A1DD3B,
+    0x735E2B97A4C45A23, 0x18727070F1BD400B, 0x1FCBACD259BF02E7,
+    0xD310A7C2CE9B6555, 0xBF983FE0FE5D8244, 0x9F74D14F7454A824,
+    0x51EBDC4AB9BA3035, 0x5C82C505DB9AB0FA, 0xFCF7FE8A3430B241,
+    0x3253A729B9BA3DDE, 0x8C74C368081B3075, 0xB9BC6C87167C33E7,
+    0x7EF48F2B83024E20, 0x11D505D4C351BD7F, 0x6568FCA92C76A243,
+    0x4DE0B0F40F32A7B8, 0x96D693460CC37E5D, 0x42E240CB63689F2F,
+    0x6D2BDCDAE2919661, 0x42880B0236E4D951, 0x5F0F4A5898171BB6,
+    0x39F890F579F92F88, 0x93C5B5F47356388B, 0x63DC359D8D231B78,
+    0xEC16CA8AEA98AD76, 0x5355F900C2A82DC7, 0x07FB9F855A997142,
+    0x5093417AA8A7ED5E, 0x7BCBC38DA25A7F3C, 0x19FC8A768CF4B6D4,
+    0x637A7780DECFC0D9, 0x8249A47AEE0E41F7, 0x79AD695501E7D1E8,
+    0x14ACBAF4777D5776, 0xF145B6BECCDEA195, 0xDABF2AC8201752FC,
+    0x24C3C94DF9C8D3F6, 0xBB6E2924F03912EA, 0x0CE26C0B95C980D9,
+    0xA49CD132BFBF7CC4, 0xE99D662AF4243939, 0x27E6AD7891165C3F,
+    0x8535F040B9744FF1, 0x54B3F4FA5F40D873, 0x72B12C32127FED2B,
+    0xEE954D3C7B411F47, 0x9A85AC909A24EAA1, 0x70AC4CD9F04F21F5,
+    0xF9B89D3E99A075C2, 0x87B3E2B2B5C907B1, 0xA366E5B8C54F48B8,
+    0xAE4A9346CC3F7CF2, 0x1920C04D47267BBD, 0x87BF02C6B49E2AE9,
+    0x092237AC237F3859, 0xFF07F64EF8ED14D0, 0x8DE8DCA9F03CC54E,
+    0x9C1633264DB49C89, 0xB3F22C3D0B0B38ED, 0x390E5FB44D01144B,
+    0x5BFEA5B4712768E9, 0x1E1032911FA78984, 0x9A74ACB964E78CB3,
+    0x4F80F7A035DAFB04, 0x6304D09A0B3738C4, 0x2171E64683023A08,
+    0x5B9B63EB9CEFF80C, 0x506AACF489889342, 0x1881AFC9A3A701D6,
+    0x6503080440750644, 0xDFD395339CDBF4A7, 0xEF927DBCF00C20F2,
+    0x7B32F7D1E03680EC, 0xB9FD7620E7316243, 0x05A7E8A57DB91B77,
+    0xB5889C6E15630A75, 0x4A750A09CE9573F7, 0xCF464CEC899A2F8A,
+    0xF538639CE705B824, 0x3C79A0FF5580EF7F, 0xEDE6C87F8477609D,
+    0x799E81F05BC93F31, 0x86536B8CF3428A8C, 0x97D7374C60087B73,
+    0xA246637CFF328532, 0x043FCAE60CC0EBA0, 0x920E449535DD359E,
+    0x70EB093B15B290CC, 0x73A1921916591CBD, 0x56436C9FE1A1AA8D,
+    0xEFAC4B70633B8F81, 0xBB215798D45DF7AF, 0x45F20042F24F1768,
+    0x930F80F4E8EB7462, 0xFF6712FFCFD75EA1, 0xAE623FD67468AA70,
+    0xDD2C5BC84BC8D8FC, 0x7EED120D54CF2DD9, 0x22FE545401165F1C,
+    0xC91800E98FB99929, 0x808BD68E6AC10365, 0xDEC468145B7605F6,
+    0x1BEDE3A3AEF53302, 0x43539603D6C55602, 0xAA969B5C691CCB7A,
+    0xA87832D392EFEE56, 0x65942C7B3C7E11AE, 0xDED2D633CAD004F6,
+    0x21F08570F420E565, 0xB415938D7DA94E3C, 0x91B859E59ECB6350,
+    0x10CFF333E0ED804A, 0x28AED140BE0BB7DD, 0xC5CC1D89724FA456,
+    0x5648F680F11A2741, 0x2D255069F0B7DAB3, 0x9BC5A38EF729ABD4,
+    0xEF2F054308F6A2BC, 0xAF2042F5CC5C2858, 0x480412BAB7F5BE2A,
+    0xAEF3AF4A563DFE43, 0x19AFE59AE451497F, 0x52593803DFF1E840,
+    0xF4F076E65F2CE6F0, 0x11379625747D5AF3, 0xBCE5D2248682C115,
+    0x9DA4243DE836994F, 0x066F70B33FE09017, 0x4DC4DE189B671A1C,
+    0x51039AB7712457C3, 0xC07A3F80C31FB4B4, 0xB46EE9C5E64A6E7C,
+    0xB3819A42ABE61C87, 0x21A007933A522A20, 0x2DF16F761598AA4F,
+    0x763C4A1371B368FD, 0xF793C46702E086A0, 0xD7288E012AEB8D31,
+    0xDE336A2A4BC1C44B, 0x0BF692B38D079F23, 0x2C604A7A177326B3,
+    0x4850E73E03EB6064, 0xCFC447F1E53C8E1B, 0xB05CA3F564268D99,
+    0x9AE182C8BC9474E8, 0xA4FC4BD4FC5558CA, 0xE755178D58FC4E76,
+    0x69B97DB1A4C03DFE, 0xF9B5B7C4ACC67C96, 0xFC6A82D64B8655FB,
+    0x9C684CB6C4D24417, 0x8EC97D2917456ED0, 0x6703DF9D2924E97E,
+    0xC547F57E42A7444E, 0x78E37644E7CAD29E, 0xFE9A44E9362F05FA,
+    0x08BD35CC38336615, 0x9315E5EB3A129ACE, 0x94061B871E04DF75,
+    0xDF1D9F9D784BA010, 0x3BBA57B68871B59D, 0xD2B7ADEEDED1F73F,
+    0xF7A255D83BC373F8, 0xD7F4F2448C0CEB81, 0xD95BE88CD210FFA7,
+    0x336F52F8FF4728E7, 0xA74049DAC312AC71, 0xA2F61BB6E437FDB5,
+    0x4F2A5CB07F6A35B3, 0x87D380BDA5BF7859, 0x16B9F7E06C453A21,
+    0x7BA2484C8A0FD54E, 0xF3A678CAD9A2E38C, 0x39B0BF7DDE437BA2,
+    0xFCAF55C1BF8A4424, 0x18FCF680573FA594, 0x4C0563B89F495AC3,
+    0x40E087931A00930D, 0x8CFFA9412EB642C1, 0x68CA39053261169F,
+    0x7A1EE967D27579E2, 0x9D1D60E5076F5B6F, 0x3810E399B6F65BA2,
+    0x32095B6D4AB5F9B1, 0x35CAB62109DD038A, 0xA90B24499FCFAFB1,
+    0x77A225A07CC2C6BD, 0x513E5E634C70E331, 0x4361C0CA3F692F12,
+    0xD941ACA44B20A45B, 0x528F7C8602C5807B, 0x52AB92BEB9613989,
+    0x9D1DFA2EFC557F73, 0x722FF175F572C348, 0x1D1260A51107FE97,
+    0x7A249A57EC0C9BA2, 0x04208FE9E8F7F2D6, 0x5A110C6058B920A0,
+    0x0CD9A497658A5698, 0x56FD23C8F9715A4C, 0x284C847B9D887AAE,
+    0x04FEABFBBDB619CB, 0x742E1E651C60BA83, 0x9A9632E65904AD3C,
+    0x881B82A13B51B9E2, 0x506E6744CD974924, 0xB0183DB56FFC6A79,
+    0x0ED9B915C66ED37E, 0x5E11E86D5873D484, 0xF678647E3519AC6E,
+    0x1B85D488D0F20CC5, 0xDAB9FE6525D89021, 0x0D151D86ADB73615,
+    0xA865A54EDCC0F019, 0x93C42566AEF98FFB, 0x99E7AFEABE000731,
+    0x48CBFF086DDF285A, 0x7F9B6AF1EBF78BAF, 0x58627E1A149BBA21,
+    0x2CD16E2ABD791E33, 0xD363EFF5F0977996, 0x0CE2A38C344A6EED,
+    0x1A804AADB9CFA741, 0x907F30421D78C5DE, 0x501F65EDB3034D07,
+    0x37624AE5A48FA6E9, 0x957BAF61700CFF4E, 0x3A6C27934E31188A,
+    0xD49503536ABCA345, 0x088E049589C432E0, 0xF943AEE7FEBF21B8,
+    0x6C3B8E3E336139D3, 0x364F6FFA464EE52E, 0xD60F6DCEDC314222,
+    0x56963B0DCA418FC0, 0x16F50EDF91E513AF, 0xEF1955914B609F93,
+    0x565601C0364E3228, 0xECB53939887E8175, 0xBAC7A9A18531294B,
+    0xB344C470397BBA52, 0x65D34954DAF3CEBD, 0xB4B81B3FA97511E2,
+    0xB422061193D6F6A7, 0x071582401C38434D, 0x7A13F18BBEDC4FF5,
+    0xBC4097B116C524D2, 0x59B97885E2F2EA28, 0x99170A5DC3115544,
+    0x6F423357E7C6A9F9, 0x325928EE6E6F8794, 0xD0E4366228B03343,
+    0x565C31F7DE89EA27, 0x30F5611484119414, 0xD873DB391292ED4F,
+    0x7BD94E1D8E17DEBC, 0xC7D9F16864A76E94, 0x947AE053EE56E63C,
+    0xC8C93882F9475F5F, 0x3A9BF55BA91F81CA, 0xD9A11FBB3D9808E4,
+    0x0FD22063EDC29FCA, 0xB3F256D8ACA0B0B9, 0xB03031A8B4516E84,
+    0x35DD37D5871448AF, 0xE9F6082B05542E4E, 0xEBFAFA33D7254B59,
+    0x9255ABB50D532280, 0xB9AB4CE57F2D34F3, 0x693501D628297551,
+    0xC62C58F97DD949BF, 0xCD454F8F19C5126A, 0xBBE83F4ECC2BDECB,
+    0xDC842B7E2819E230, 0xBA89142E007503B8, 0xA3BC941D0A5061CB,
+    0xE9F6760E32CD8021, 0x09C7E552BC76492F, 0x852F54934DA55CC9,
+    0x8107FCCF064FCF56, 0x098954D51FFF6580, 0x23B70EDB1955C4BF,
+    0xC330DE426430F69D, 0x4715ED43E8A45C0A, 0xA8D7E4DAB780A08D,
+    0x0572B974F03CE0BB, 0xB57D2E985E1419C7, 0xE8D9ECBE2CF3D73F,
+    0x2FE4B17170E59750, 0x11317BA87905E790, 0x7FBF21EC8A1F45EC,
+    0x1725CABFCB045B00, 0x964E915CD5E2B207, 0x3E2B8BCBF016D66D,
+    0xBE7444E39328A0AC, 0xF85B2B4FBCDE44B7, 0x49353FEA39BA63B1,
+    0x1DD01AAFCD53486A, 0x1FCA8A92FD719F85, 0xFC7C95D827357AFA,
+    0x18A6A990C8B35EBD, 0xCCCB7005C6B9C28D, 0x3BDBB92C43B17F26,
+    0xAA70B5B4F89695A2, 0xE94C39A54A98307F, 0xB7A0B174CFF6F36E,
+    0xD4DBA84729AF48AD, 0x2E18BC1AD9704A68, 0x2DE0966DAF2F8B1C,
+    0xB9C11D5B1E43A07E, 0x64972D68DEE33360, 0x94628D38D0C20584,
+    0xDBC0D2B6AB90A559, 0xD2733C4335C6A72F, 0x7E75D99D94A70F4D,
+    0x6CED1983376FA72B, 0x97FCAACBF030BC24, 0x7B77497B32503B12,
+    0x8547EDDFB81CCB94, 0x79999CDFF70902CB, 0xCFFE1939438E9B24,
+    0x829626E3892D95D7, 0x92FAE24291F2B3F1, 0x63E22C147B9C3403,
+    0xC678B6D860284A1C, 0x5873888850659AE7, 0x0981DCD296A8736D,
+    0x9F65789A6509A440, 0x9FF38FED72E9052F, 0xE479EE5B9930578C,
+    0xE7F28ECD2D49EECD, 0x56C074A581EA17FE, 0x5544F7D774B14AEF,
+    0x7B3F0195FC6F290F, 0x12153635B2C0CF57, 0x7F5126DBBA5E0CA7,
+    0x7A76956C3EAFB413, 0x3D5774A11D31AB39, 0x8A1B083821F40CB4,
+    0x7B4A38E32537DF62, 0x950113646D1D6E03, 0x4DA8979A0041E8A9,
+    0x3BC36E078F7515D7, 0x5D0A12F27AD310D1, 0x7F9D1A2E1EBE1327,
+    0xDA3A361B1C5157B1, 0xDCDD7D20903D0C25, 0x36833336D068F707,
+    0xCE68341F79893389, 0xAB9090168DD05F34, 0x43954B3252DC25E5,
+    0xB438C2B67F98E5E9, 0x10DCD78E3851A492, 0xDBC27AB5447822BF,
+    0x9B3CDB65F82CA382, 0xB67B7896167B4C84, 0xBFCED1B0048EAC50,
+    0xA9119B60369FFEBD, 0x1FFF7AC80904BF45, 0xAC12FB171817EEE7,
+    0xAF08DA9177DDA93D, 0x1B0CAB936E65C744, 0xB559EB1D04E5E932,
+    0xC37B45B3F8D6F2BA, 0xC3A9DC228CAAC9E9, 0xF3B8B6675A6507FF,
+    0x9FC477DE4ED681DA, 0x67378D8ECCEF96CB, 0x6DD856D94D259236,
+    0xA319CE15B0B4DB31, 0x073973751F12DD5E, 0x8A8E849EB32781A5,
+    0xE1925C71285279F5, 0x74C04BF1790C0EFE, 0x4DDA48153C94938A,
+    0x9D266D6A1CC0542C, 0x7440FB816508C4FE, 0x13328503DF48229F,
+    0xD6BF7BAEE43CAC40, 0x4838D65F6EF6748F, 0x1E152328F3318DEA,
+    0x8F8419A348F296BF, 0x72C8834A5957B511, 0xD7A023A73260B45C,
+    0x94EBC8ABCFB56DAE, 0x9FC10D0F989993E0, 0xDE68A2355B93CAE6,
+    0xA44CFE79AE538BBE, 0x9D1D84FCCE371425, 0x51D2B1AB2DDFB636,
+    0x2FD7E4B9E72CD38C, 0x65CA5B96B7552210, 0xDD69A0D8AB3B546D,
+    0x604D51B25FBF70E2, 0x73AA8A564FB7AC9E, 0x1A8C1E992B941148,
+    0xAAC40A2703D9BEA0, 0x764DBEAE7FA4F3A6, 0x1E99B96E70A9BE8B,
+    0x2C5E9DEB57EF4743, 0x3A938FEE32D29981, 0x26E6DB8FFDF5ADFE,
+    0x469356C504EC9F9D, 0xC8763C5B08D1908C, 0x3F6C6AF859D80055,
+    0x7F7CC39420A3A545, 0x9BFB227EBDF4C5CE, 0x89039D79D6FC5C5C,
+    0x8FE88B57305E2AB6, 0xA09E8C8C35AB96DE, 0xFA7E393983325753,
+    0xD6B6D0ECC617C699, 0xDFEA21EA9E7557E3, 0xB67C1FA481680AF8,
+    0xCA1E3785A9E724E5, 0x1CFC8BED0D681639, 0xD18D8549D140CAEA,
+    0x4ED0FE7E9DC91335, 0xE4DBF0634473F5D2, 0x1761F93A44D5AEFE,
+    0x53898E4C3910DA55, 0x734DE8181F6EC39A, 0x2680B122BAA28D97,
+    0x298AF231C85BAFAB, 0x7983EED3740847D5, 0x66C1A2A1A60CD889,
+    0x9E17E49642A3E4C1, 0xEDB454E7BADC0805, 0x50B704CAB602C329,
+    0x4CC317FB9CDDD023, 0x66B4835D9EAFEA22, 0x219B97E26FFC81BD,
+    0x261E4E4C0A333A9D, 0x1FE2CCA76517DB90, 0xD7504DFA8816EDBB,
+    0xB9571FA04DC089C8, 0x1DDC0325259B27DE, 0xCF3F4688801EB9AA,
+    0xF4F5D05C10CAB243, 0x38B6525C21A42B0E, 0x36F60E2BA4FA6800,
+    0xEB3593803173E0CE, 0x9C4CD6257C5A3603, 0xAF0C317D32ADAA8A,
+    0x258E5A80C7204C4B, 0x8B889D624D44885D, 0xF4D14597E660F855,
+    0xD4347F66EC8941C3, 0xE699ED85B0DFB40D, 0x2472F6207C2D0484,
+    0xC2A1E7B5B459AEB5, 0xAB4F6451CC1D45EC, 0x63767572AE3D6174,
+    0xA59E0BD101731A28, 0x116D0016CB948F09, 0x2CF9C8CA052F6E9F,
+    0x0B090A7560A968E3, 0xABEEDDB2DDE06FF1, 0x58EFC10B06A2068D,
+    0xC6E57A78FBD986E0, 0x2EAB8CA63CE802D7, 0x14A195640116F336,
+    0x7C0828DD624EC390, 0xD74BBE77E6116AC7, 0x804456AF10F5FB53,
+    0xEBE9EA2ADF4321C7, 0x03219A39EE587A30, 0x49787FEF17AF9924,
+    0xA1E9300CD8520548, 0x5B45E522E4B1B4EF, 0xB49C3B3995091A36,
+    0xD4490AD526F14431, 0x12A8F216AF9418C2, 0x001F837CC7350524,
+    0x1877B51E57A764D5, 0xA2853B80F17F58EE, 0x993E1DE72D36D310,
+    0xB3598080CE64A656, 0x252F59CF0D9F04BB, 0xD23C8E176D113600,
+    0x1BDA0492E7E4586E, 0x21E0BD5026C619BF, 0x3B097ADAF088F94E,
+    0x8D14DEDB30BE846E, 0xF95CFFA23AF5F6F4, 0x3871700761B3F743,
+    0xCA672B91E9E4FA16, 0x64C8E531BFF53B55, 0x241260ED4AD1E87D,
+    0x106C09B972D2E822, 0x7FBA195410E5CA30, 0x7884D9BC6CB569D8,
+    0x0647DFEDCD894A29, 0x63573FF03E224774, 0x4FC8E9560F91B123,
+    0x1DB956E450275779, 0xB8D91274B9E9D4FB, 0xA2EBEE47E2FBFCE1,
+    0xD9F1F30CCD97FB09, 0xEFED53D75FD64E6B, 0x2E6D02C36017F67F,
+    0xA9AA4D20DB084E9B, 0xB64BE8D8B25396C1, 0x70CB6AF7C2D5BCF0,
+    0x98F076A4F7A2322E, 0xBF84470805E69B5F, 0x94C3251F06F90CF3,
+    0x3E003E616A6591E9, 0xB925A6CD0421AFF3, 0x61BDD1307C66E300,
+    0xBF8D5108E27E0D48, 0x240AB57A8B888B20, 0xFC87614BAF287E07,
+    0xEF02CDD06FFDB432, 0xA1082C0466DF6C0A, 0x8215E577001332C8,
+    0xD39BB9C3A48DB6CF, 0x2738259634305C14, 0x61CF4F94C97DF93D,
+    0x1B6BACA2AE4E125B, 0x758F450C88572E0B, 0x959F587D507A8359,
+    0xB063E962E045F54D, 0x60E8ED72C0DFF5D1, 0x7B64978555326F9F,
+    0xFD080D236DA814BA, 0x8C90FD9B083F4558, 0x106F72FE81E2C590,
+    0x7976033A39F7D952, 0xA4EC0132764CA04B, 0x733EA705FAE4FA77,
+    0xB4D8F77BC3E56167, 0x9E21F4F903B33FD9, 0x9D765E419FB69F6D,
+    0xD30C088BA61EA5EF, 0x5D94337FBFAF7F5B, 0x1A4E4822EB4D7A59,
+    0x6FFE73E81B637FB3, 0xDDF957BC36D8B9CA, 0x64D0E29EEA8838B3,
+    0x08DD9BDFD96B9F63, 0x087E79E5A57D1D13, 0xE328E230E3E2B3FB,
+    0x1C2559E30F0946BE, 0x720BF5F26F4D2EAA, 0xB0774D261CC609DB,
+    0x443F64EC5A371195, 0x4112CF68649A260E, 0xD813F2FAB7F5C5CA,
+    0x660D3257380841EE, 0x59AC2C7873F910A3, 0xE846963877671A17,
+    0x93B633ABFA3469F8, 0xC0C0F5A60EF4CDCF, 0xCAF21ECD4377B28C,
+    0x57277707199B8175, 0x506C11B9D90E8B1D, 0xD83CC2687A19255F,
+    0x4A29C6465A314CD1, 0xED2DF21216235097, 0xB5635C95FF7296E2,
+    0x22AF003AB672E811, 0x52E762596BF68235, 0x9AEBA33AC6ECC6B0,
+    0x944F6DE09134DFB6, 0x6C47BEC883A7DE39, 0x6AD047C430A12104,
+    0xA5B1CFDBA0AB4067, 0x7C45D833AFF07862, 0x5092EF950A16DA0B,
+    0x9338E69C052B8E7B, 0x455A4B4CFE30E3F5, 0x6B02E63195AD0CF8,
+    0x6B17B224BAD6BF27, 0xD1E0CCD25BB9C169, 0xDE0C89A556B9AE70,
+    0x50065E535A213CF6, 0x9C1169FA2777B874, 0x78EDEFD694AF1EED,
+    0x6DC93D9526A50E68, 0xEE97F453F06791ED, 0x32AB0EDB696703D3,
+    0x3A6853C7E70757A7, 0x31865CED6120F37D, 0x67FEF95D92607890,
+    0x1F2B1D1F15F6DC9C, 0xB69E38A8965C6B65, 0xAA9119FF184CCCF4,
+    0xF43C732873F24C13, 0xFB4A3D794A9A80D2, 0x3550C2321FD6109C,
+    0x371F77E76BB8417E, 0x6BFA9AAE5EC05779, 0xCD04F3FF001A4778,
+    0xE3273522064480CA, 0x9F91508BFFCFC14A, 0x049A7F41061A9E60,
+    0xFCB6BE43A9F2FE9B, 0x08DE8A1C7797DA9B, 0x8F9887E6078735A1,
+    0xB5B4071DBFC73A66, 0x230E343DFBA08D33, 0x43ED7F5A0FAE657D,
+    0x3A88A0FBBCB05C63, 0x21874B8B4D2DBC4F, 0x1BDEA12E35F6A8C9,
+    0x53C065C6C8E63528, 0xE34A1D250E7A8D6B, 0xD6B04D3B7651DD7E,
+    0x5E90277E7CB39E2D, 0x2C046F22062DC67D, 0xB10BB459132D0A26,
+    0x3FA9DDFB67E2F199, 0x0E09B88E1914F7AF, 0x10E8B35AF3EEAB37,
+    0x9EEDECA8E272B933, 0xD4C718BC4AE8AE5F, 0x81536D601170FC20,
+    0x91B534F885818A06, 0xEC8177F83F900978, 0x190E714FADA5156E,
+    0xB592BF39B0364963, 0x89C350C893AE7DC1, 0xAC042E70F8B383F2,
+    0xB49B52E587A1EE60, 0xFB152FE3FF26DA89, 0x3E666E6F69AE2C15,
+    0x3B544EBE544C19F9, 0xE805A1E290CF2456, 0x24B33C9D7ED25117,
+    0xE74733427B72F0C1, 0x0A804D18B7097475, 0x57E3306D881EDB4F,
+    0x4AE7D6A36EB5DBCB, 0x2D8D5432157064C8, 0xD1E649DE1E7F268B,
+    0x8A328A1CEDFE552C, 0x07A3AEC79624C7DA, 0x84547DDC3E203C94,
+    0x990A98FD5071D263, 0x1A4FF12616EEFC89, 0xF6F7FD1431714200,
+    0x30C05B1BA332F41C, 0x8D2636B81555A786, 0x46C9FEB55D120902,
+    0xCCEC0A73B49C9921, 0x4E9D2827355FC492, 0x19EBB029435DCB0F,
+    0x4659D2B743848A2C, 0x963EF2C96B33BE31, 0x74F85198B05A2E7D,
+    0x5A0F544DD2B1FB18, 0x03727073C2E134B1, 0xC7F6AA2DE59AEA61,
+    0x352787BAA0D7C22F, 0x9853EAB63B5E0B35, 0xABBDCDD7ED5C0860,
+    0xCF05DAF5AC8D77B0, 0x49CAD48CEBF4A71E, 0x7A4C10EC2158C4A6,
+    0xD9E92AA246BF719E, 0x13AE978D09FE5557, 0x730499AF921549FF,
+    0x4E4B705B92903BA4, 0xFF577222C14F0A3A, 0x55B6344CF97AAFAE,
+    0xB862225B055B6960, 0xCAC09AFBDDD2CDB4, 0xDAF8E9829FE96B5F,
+    0xB5FDFC5D3132C498, 0x310CB380DB6F7503, 0xE87FBB46217A360E,
+    0x2102AE466EBB1148, 0xF8549E1A3AA5E00D, 0x07A69AFDCC42261A,
+    0xC4C118BFE78FEAAE, 0xF9F4892ED96BD438, 0x1AF3DBE25D8F45DA,
+    0xF5B4B0B0D2DEEEB4, 0x962ACEEFA82E1C84, 0x046E3ECAAF453CE9,
+    0xF05D129681949A4C, 0x964781CE734B3C84, 0x9C2ED44081CE5FBD,
+    0x522E23F3925E319E, 0x177E00F9FC32F791, 0x2BC60A63A6F3B3F2,
+    0x222BBFAE61725606, 0x486289DDCC3D6780, 0x7DC7785B8EFDFC80,
+    0x8AF38731C02BA980, 0x1FAB64EA29A2DDF7, 0xE4D9429322CD065A,
+    0x9DA058C67844F20C, 0x24C0E332B70019B0, 0x233003B5A6CFE6AD,
+    0xD586BD01C5C217F6, 0x5E5637885F29BC2B, 0x7EBA726D8C94094B,
+    0x0A56A5F0BFE39272, 0xD79476A84EE20D06, 0x9E4C1269BAA4BF37,
+    0x17EFEE45B0DEE640, 0x1D95B0A5FCF90BC6, 0x93CBE0B699C2585D,
+    0x65FA4F227A2B6D79, 0xD5F9E858292504D5, 0xC2B5A03F71471A6F,
+    0x59300222B4561E00, 0xCE2F8642CA0712DC, 0x7CA9723FBB2E8988,
+    0x2785338347F2BA08, 0xC61BB3A141E50E8C, 0x150F361DAB9DEC26,
+    0x9F6A419D382595F4, 0x64A53DC924FE7AC9, 0x142DE49FFF7A7C3D,
+    0x0C335248857FA9E7, 0x0A9C32D5EAE45305, 0xE6C42178C4BBB92E,
+    0x71F1CE2490D20B07, 0xF1BCC3D275AFE51A, 0xE728E8C83C334074,
+    0x96FBF83A12884624, 0x81A1549FD6573DA5, 0x5FA7867CAF35E149,
+    0x56986E2EF3ED091B, 0x917F1DD5F8886C61, 0xD20D8C88C8FFE65F,
+    0x31D71DCE64B2C310, 0xF165B587DF898190, 0xA57E6339DD2CF3A0,
+    0x1EF6E6DBB1961EC9, 0x70CC73D90BC26E24, 0xE21A6B35DF0C3AD7,
+    0x003A93D8B2806962, 0x1C99DED33CB890A1, 0xCF3145DE0ADD4289,
+    0xD0E4427A5514FB72, 0x77C621CC9FB3A483, 0x67A34DAC4356550B,
+    0xF8D626AAAF278509,
+};
+
+static bool IsEnpassantLegal(Game *g) {
+  if (!g->canEnpassant) {
+    return false;
+  }
+
+  // Polyglot spec: en passant key is included only if the player to move
+  // has a pawn adjacent to the en passant target square.
+  int epFile = g->enPassant.file;
+  int epRank = g->enPassant.rank;
+
+  // The capturing pawn sits one rank away from the ep target:
+  //   white to move: pawn is one rank below (epRank - 1)
+  //   black to move: pawn is one rank above (epRank + 1)
+  int pawnRank = g->turn ? (epRank - 1) : (epRank + 1);
+
+  if (pawnRank < 0 || pawnRank > 7) {
+    return false;
+  }
 
+  bool leftSide = false;
+  bool rightSide = false;
+
+  if (epFile > 0) {
+    leftSide = (g->PieceBitboards[g->turn][PAWN] &
+                (1ULL << (pawnRank * 8 + epFile - 1))) > 0;
+  }
+  if (epFile < 7) {
+    rightSide = (g->PieceBitboards[g->turn][PAWN] &
+                 (1ULL << (pawnRank * 8 + epFile + 1))) > 0;
+  }
+
+  return leftSide || rightSide;
+}
+
+// PolyglotRandom64 layout (standard Polyglot spec):
+//   [0..767]   piece keys, kind = (pieceType-1)*2 + color:
+//              [0-63] black pawn, [64-127] white pawn, [128-191] black knight,
+//              [192-255] white knight, [256-319] black bishop, [320-383] white bishop,
+//              [384-447] black rook, [448-511] white rook, [512-575] black queen,
+//              [576-639] white queen, [640-703] black king, [704-767] white king
+//   [768]      white kingside castling
+//   [769]      white queenside castling
+//   [770]      black kingside castling
+//   [771]      black queenside castling
+//   [772..779] en passant file a-h
+//   [780]      side to move (XORed when white to move)
 void InitZobrist() {
-  std::mt19937_64 rng(1234567); // fixed seed
+  int idx = 0;
 
-  for (int color = 0; color < 2; color++) {
-    for (int piece = 0; piece < 7; piece++) {
-      for (int square = 0; square < 64; square++) {
-        PieceKeys[color][piece][square] = rng();
-      }
+  // Piece keys: interleaved by kind = (pieceType-1)*2 + color
+  for (int kind = 0; kind < 12; ++kind) {
+    int color = kind % 2;          // 0=black, 1=white
+    int pieceType = (kind / 2) + 1; // PAWN=1..KING=6
+    for (int square = 0; square < 64; ++square) {
+      PieceKeys[color][pieceType][square] = PolyglotRandom64[idx++];
     }
   }
 
-  SideKey = rng();
-
-  for (int i = 0; i < 16; i++) {
-    CastleKeys[i] = rng();
+  // Castling keys (one per right, indices 768-771)
+  for (int i = 0; i < 4; ++i) {
+    CastleKeys[i] = PolyglotRandom64[idx++];
   }
 
-  for (int i = 0; i < 8; i++) {
-    EnPassantKeys[i] = rng();
+  // En passant keys (one per file, indices 772-779)
+  for (int file = 0; file < 8; ++file) {
+    EnPassantKeys[file] = PolyglotRandom64[idx++];
   }
+
+  // Side to move key (index 780)
+  SideKey = PolyglotRandom64[idx];
 }
 
 uint64_t GenerateZobristKey(Game *b) {
@@ -36,36 +352,30 @@ uint64_t GenerateZobristKey(Game *b) {
 
   for (int square = 0; square < 64; square++) {
     Piece p = b->pieces[square];
-
-    if (p.type == NONEPIECE)
+    if (p.type == NONEPIECE) {
       continue;
-
+    }
     key ^= PieceKeys[p.color][p.type][square];
   }
 
-  // side to move
-  if (b->turn)
+  if (b->turn) {
     key ^= SideKey;
+  }
 
-  // castling
-  int castle = 0;
-
-  if (b->whiteCastleKing)
-    castle |= 1;
-
-  if (b->whiteCastleQueen)
-    castle |= 2;
-
-  if (b->blackCastleKing)
-    castle |= 4;
-
-  if (b->blackCastleQueen)
-    castle |= 8;
-
-  key ^= CastleKeys[castle];
+  if (b->whiteCastleKing) {
+    key ^= CastleKeys[0];
+  }
+  if (b->whiteCastleQueen) {
+    key ^= CastleKeys[1];
+  }
+  if (b->blackCastleKing) {
+    key ^= CastleKeys[2];
+  }
+  if (b->blackCastleQueen) {
+    key ^= CastleKeys[3];
+  }
 
-  // en passant
-  if (b->canEnpassant) {
+  if (b->canEnpassant && IsEnpassantLegal(b)) {
     key ^= EnPassantKeys[b->enPassant.file];
   }
 
diff --git a/src/zobrist.hpp b/src/zobrist.hpp
index 575d912..e23facf 100644
--- a/src/zobrist.hpp
+++ b/src/zobrist.hpp
@@ -1,11 +1,7 @@
 #pragma once
-#include "board/board.hpp"
 #include <cstdint>
 
-extern uint64_t PieceKeys[2][7][64];
-extern uint64_t SideKey;
-extern uint64_t CastleKeys[16];
-extern uint64_t EnPassantKeys[8];
+struct Game;
 
 void InitZobrist();
 uint64_t GenerateZobristKey(Game *b);