diff --git a/contracts/standard/rng/BlockhashRNGFallbackRange.sol b/contracts/standard/rng/BlockhashRNGFallbackRange.sol new file mode 100644 index 00000000..7913a970 --- /dev/null +++ b/contracts/standard/rng/BlockhashRNGFallbackRange.sol @@ -0,0 +1,45 @@ + /** + * @authors: [@remedcu] + * @reviewers: [@clesaege] + * @auditors: [] + * @bounties: [] + * @deployments: [] + */ + +pragma solidity ^0.4.15; + +import "./BlockhashRNG.sol"; + +/** + * @title Random Number Generator using blockhash with fallback from the last 256 blockhash mined. + * @author Shebin John - + * + * Random Number Generator returning the blockhash with a backup behaviour. + * This contract implements the RNG standard and gives parties incentives to save the blockhash to avoid it to become unreachable after 256 blocks. + * In case no one called it within the 256 blocks, it returns the blockhash from any one of the last mined 256 blocks. + * Thus allowing the contract to still return a value even after 256 blocks. + * Allows saving the random number for use in the future. + * The first party to call the save function gets the reward. + * This contract must be used when returning 0 is a worse failure mode than returning another blockhash. + * Note that if someone calls it within the timeframe, this contracts acts exactly as BlockHashRNG. + */ +contract BlockHashRNGFallback is BlockHashRNG { + + /** @dev Save the random number for this blockhash and give the reward to the caller. + * @param _block Block the random number is linked to. + */ + function saveRN(uint _block) public { + if (_block < block.number && randomNumber[_block] == 0) { // If the random number is not already set and can be. + // Returns the blockhash of _block if accessible (one of the last 256 blocks). + // If the blockhash hasn't been saved in time, return a blockhash of a block in range as a fallback. + randomNumber[_block] = uint(blockhash((block.number-1) - (block.number-1-_block)%256)); + } + + if (randomNumber[_block] != 0) { // If the random number is set. + uint rewardToSend = reward[_block]; + reward[_block] = 0; + msg.sender.send(rewardToSend); // Note that the use of send is on purpose as we don't want to block in case the msg.sender has a fallback issue. + } + } + +}