src/engine/transposition_table.c


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#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;
}