pyth-crosschain/target_chains/ethereum/entropy_sdk/solidity/Prng.sol

28 lines
858 B
Solidity

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;
/// A pseudorandom number generator powered by a seed.
/// This
library Prng {
uint256 public constant MAX_UINT_256 = (uint256) (~(uint256)(0));
function next(PrngState memory state) public returns (PrngState memory nextState, uint256 val) {
val = (uint256) (state.rand);
nextState = PrngState(keccak256(abi.encodePacked((state.rand))));
}
function draw(PrngState memory state, uint256 max) public returns (PrngState memory nextState, uint256 val) {
uint256 bits;
nextState = state;
do {
(nextState, bits) = next(nextState);
val = bits % max;
// FIXME: check boundary condition. this may be off by 1
} while (bits - val > MAX_UINT_256 - max);
}
}
struct PrngState {
bytes32 rand;
}