From a0970bddbd9f6b97b6a12ba7f73fd1810a2e1e1b Mon Sep 17 00:00:00 2001
From: Aargh Rai <aargh.rai+git@gmail.com>
Date: Sun, 19 Jul 2026 17:52:26 +0530
Subject: ttable lookup & probe

---
 src/engine/ttable.c | 90 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 src/engine/ttable.c

(limited to 'src/engine/ttable.c')

diff --git a/src/engine/ttable.c b/src/engine/ttable.c
new file mode 100644
index 0000000..31bdd72
--- /dev/null
+++ b/src/engine/ttable.c
@@ -0,0 +1,90 @@
+#include "engine/ttable.h"
+
+void ttable_init() {
+  tbucket_t *table = calloc(TABLE_SIZE * sizeof(*table));
+
+  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;
+}
+
+void ttable_store(
+  ttable_t *ttable,
+  u64 key,
+  move_t move,
+  i16 score,
+  i16 eval,
+  u16 depth,
+  u16 generation,
+  u8 flag
+) {
+    tbucket_t *bucket = ttable + (key & MASK);
+    tentry_t *best = bucket.entries;
+
+    for (int i = 1; i < TT_BUCKET_SIZE; i++) {
+      if (bucket.entries[i].depth >= best->depth) continue;
+      best = bucket.entries + i;
+    }
+
+    tentry_t object;
+    object.move = move;
+    object.score = score;
+    object.eval = eval;
+    object.depth = depth;
+    object.flag = flag;
+    object.generation = generation;
+
+    memcpy(best, &object, sizeof(object));
+    atomic_store_explicit(&best->key, key, memory_order_release);
+}
+
+tentry_t *ttable_probe(ttable_t *table, u64 key) {
+    tbucket_t *bucket = ttable + key & MASK;
+
+    for (int i = 0; i < TT_BUCKET_SIZE; i++) {
+      if (atomic_load_explicit(
+        &(bucket.entries + i)->key,
+        memory_order_acquire
+      ) != key) continue;
+      return bucket.entries + i;
+    }
+
+    return NULL;
+}
-- 
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