2 files changed, 83 insertions, 0 deletions
diff --git a/src/zobrist/zobrist.cpp b/src/zobrist/zobrist.cpp
new file mode 100644
index 0000000..cfc7769
--- /dev/null
+++ b/src/zobrist/zobrist.cpp
@@ -0,0 +1,72 @@
+#include "zobrist.hpp"
+#include "board.hpp"
+
+#include <random>
+
+uint64_t PieceKeys[2][7][64];
+uint64_t SideKey;
+uint64_t CastleKeys[16];
+uint64_t EnPassantKeys[8];
+
+void InitZobrist() {
+  std::mt19937_64 rng(1234567); // fixed seed
+
+  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();
+      }
+    }
+  }
+
+  SideKey = rng();
+
+  for (int i = 0; i < 16; i++) {
+    CastleKeys[i] = rng();
+  }
+
+  for (int i = 0; i < 8; i++) {
+    EnPassantKeys[i] = rng();
+  }
+}
+
+uint64_t GenerateZobristKey(Game *b) {
+  uint64_t key = 0;
+
+  for (int square = 0; square < 64; square++) {
+    Piece p = b->pieces[square];
+
+    if (p.type == NONEPIECE)
+      continue;
+
+    key ^= PieceKeys[p.color][p.type][square];
+  }
+
+  // side to move
+  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];
+
+  // en passant
+  if (b->canEnpassant) {
+    key ^= EnPassantKeys[b->enPassant.file];
+  }
+
+  return key;
+}
diff --git a/src/zobrist/zobrist.hpp b/src/zobrist/zobrist.hpp
new file mode 100644
index 0000000..8de9d42
--- /dev/null
+++ b/src/zobrist/zobrist.hpp
@@ -0,0 +1,11 @@
+#pragma once
+#include "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];
+
+void InitZobrist();
+uint64_t GenerateZobristKey(Game *b);