Solidity Gambling Smart Contract

Gambling.sol

contract Gamble {
    function Gamble() {
        owner = msg.sender;
        address nameReg = 0x72ba7d8e73fe8eb666ea66babc8116a41bfb10e2;
        nameReg.callstring32string32("register", "UltimateGamble");
    }
    function gamble(uint luckyNumber) {
        value = value+ msg.value;
        hash randomness = sha3(block.prevhash ^ hash(msg.sender) ^ luckyNumber);
        if (msg.value >= 1000000000000000000 && ((randomness & 0xff) < hash(0x20))) {
            lostValue = lostValue + value / 2;
            msg.sender.send(value - (value / 2));
            value = 0;
        }
    }
    function withdraw() {
          owner.send(lostValue);
          lostValue = 0;
    }
    uint value;
}