From c9d9bddf3df97ef7987c9824747ec1602522b542 Mon Sep 17 00:00:00 2001
From: Aargh Rai <aargh.rai+git@gmail.com>
Date: Sat, 18 Jul 2026 18:45:15 +0530
Subject: zobrist hashing

---
 src/engine/moves/magic.c         | 14 +------------
 src/engine/transposition_table.c | 44 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 13 deletions(-)
 create mode 100644 src/engine/transposition_table.c

(limited to 'src/engine')

diff --git a/src/engine/moves/magic.c b/src/engine/moves/magic.c
index 43f4a32..74b2c72 100644
--- a/src/engine/moves/magic.c
+++ b/src/engine/moves/magic.c
@@ -1,4 +1,5 @@
 #include "engine/magic.h"
+#include "random.h"
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>
@@ -8,19 +9,6 @@ static magic_t bishop_table[64];
 static bitboard_t *rook_attacks_flat;
 static bitboard_t *bishop_attacks_flat;
 
-static u64 rng_state = 1070399;
-
-static u64 random_u64(void) {
-  rng_state ^= rng_state << 13;
-  rng_state ^= rng_state >> 7;
-  rng_state ^= rng_state << 17;
-  return rng_state;
-}
-
-static u64 random_magic(void) {
-  return random_u64() & random_u64() & random_u64();
-}
-
 static bitboard_t compute_rook_mask(int sq) {
   bitboard_t mask = 0;
   int rank = sq / 8, file = sq % 8;
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;
+}
-- 
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