library MerkleTreiTree {
  static function addTxid(bytes txid, bytes oldMerkleRoot, bytes merklePath) : bytes {
    Ripemd160 oldMerkleValue = hash160(b'0000000000000000000000000000000000000000000000000000000000000000');
    Ripemd160 newMerkleValue = hash160(txid);
    int key = Utils.fromLEUnsigned(txid);
    loop (32) : i {
        int index = key % 256;
        key = key / 256;
        int rightNum = 255 - index;
        int start = (i * 5100);
        int pos = start + index * 20;
        bytes leftNeighbor = merklePath[start : pos];
        bytes rightNeighbor = merklePath[pos : pos + rightNum * 20];
        oldMerkleValue = hash160(leftNeighbor + oldMerkleValue + rightNeighbor);
        newMerkleValue = hash160(leftNeighbor + newMerkleValue + rightNeighbor);
      }
    require(newMerkleValue != oldMerkleRoot);
    require(oldMerkleValue == oldMerkleRoot);
    return newMerkleValue;
  }
}