contract.rad

contract PowMint(int REWARD, bytes36 CONTRACT_REF, bytes36 TOKEN_REF, int TARGET, bytes4 HEIGHT, int MAX_HEIGHT)
function (bytes4 nonce, bytes32 inputHash, bytes32 outputHash, int outputIndex) {
    // Height will be incremented on each spend
    bytes4 height = HEIGHT;

    // Remaining state is constant, but separated from the code script so code script hash is consistent for all contracts
    bytes36 contractRef = pushInputRefSingleton(CONTRACT_REF);
    bytes36 tokenRef = pushInputRef(TOKEN_REF);
    int maxHeight = MAX_HEIGHT;
    int reward = REWARD;
    int target = TARGET;
    stateSeparator;

    // PoW
    bytes hash = hash256(
        sha256(tx.inputs[this.activeInputIndex].outpointTransactionHash + contractRef) +
        sha256(inputHash + outputHash) +
        nonce
    ).reverse();

    bytes next8Bytes, bytes firstFourBytes = hash.split(20)[1].split(8);

    // Minimum difficulty requires first four bytes to be zero
    require(firstFourBytes == 0x00000000);

    // Numbers are signed so make sure it's a positive value less than the target
    int value = int(next8Bytes);
    require(value >= 0);
    require(value <= target);

    // Check input and output script hashes exist
    require(tx.inputs.codeScriptCount(inputHash) > 0);
    require(tx.outputs.codeScriptCount(outputHash) > 0);

    // Check reward outputs
    bytes32 rewardCSH = hash256(0xd0 + tokenRef + 0xdec0e9aa76e378e4a269e69d); // FT script
    require(tx.outputs.codeScriptValueSum(rewardCSH) == reward);

    // Restrict token ref usage
    int newHeight = int(height) + 1;
    bool finalMint = newHeight == maxHeight;
    require(tx.outputs.refOutputCount(tokenRef) == int(!finalMint) + tx.outputs.codeScriptCount(rewardCSH));

    if (finalMint) {
        // Contract must be burned to unspendable output on final mint
        require(tx.outputs[outputIndex].lockingBytecode == 0xd8 + contractRef + 0x6a);
    } else {
        // Restrict contract ref usage
        require(tx.outputs.refOutputCount(contractRef) == 1);

        // Create new state script
        bytes newState = 0x04 + bytes4(newHeight) + tx.inputs[this.activeInputIndex].stateScript.split(5)[1];
        require(tx.outputs[outputIndex].stateScript == newState);

        // Contract can't be changed
        require(tx.outputs[outputIndex].codeScript == tx.inputs[this.activeInputIndex].codeScript);
        require(tx.outputs[outputIndex].value == 1);
    }
}