GoCryptobotRandom.sol

uint commitmentNumber;
bytes32 randomBytes;

function commitment() public onlyOperator {
    commitmentNumber = block.number;
}

function _initRandom() internal {
    require(commitmentNumber < block.number);

    if (commitmentNumber < block.number - 255) {
        randomBytes = block.blockhash(block.number - 1);
    } else {
        randomBytes = block.blockhash(commitmentNumber);
    }
}

function _random256() internal returns(uint256) {
    randomBytes = keccak256(randomBytes);
    return uint256(randomBytes);
}