zobrist hashing

1 files changed, 44 insertions, 0 deletions

diff --git a/src/engine/transposition_table.c b/src/engine/transposition_table.c
new file mode 100644
index 0000000..1afbc81
--- /dev/null
+++ b/src/engine/transposition_table.c
@@ -0,0 +1,44 @@
+#include "engine/transposition_table.h"
+
+void transposition_table_init() {
+  for (int i = 0; i < PIECE_TYPE_COUNT; i++) {
+    for (int j = 0; j < 64; j++) {
+      zobrist_keys.piece[i][j] = random_u64();
+    }
+  }
+  for (int i = 0; i < CASTLE_COUNT; i++) {
+    zobrist_keys.castle[i] = random_u64();
+  }
+  for (int i = 0; i < TURN_COUNT; i++) {
+    zobrist_keys.turn[i] = random_u64();
+  }
+  for (int i = 0; i < 64; i++) {
+    zobrist_keys.en_passant[i] = random_u64();
+  }
+}
+
+u64 zobrist_hash(position_t position) {
+  u64 output = 0;
+  for (int i = 0; i < 64; i++) {
+    int piece_type = find_piece_on_square(&position, i);
+    output ^= zobrist_keys.piece[piece_type][i];
+  }
+
+  if (position.castling & WHITE_SHORT_CASTLE) {
+    output ^= zobrist_keys.castle[0];
+  }
+  if (position.castling & WHITE_LONG_CASTLE) {
+    output ^= zobrist_keys.castle[1];
+  }
+  if (position.castling & BLACK_SHORT_CASTLE) {
+    output ^= zobrist_keys.castle[2];
+  }
+  if (position.castling & BLACK_LONG_CASTLE) {
+    output ^= zobrist_keys.castle[3];
+  }
+
+  output ^= zobrist_keys.turn[position.turn];
+  output ^= zobrist_keys.en_passant[position.passantable_file];
+
+  return output;
+}