fhevm-solidity/contracts/OptimisticRequire.sol

// SPDX-License-Identifier: BSD-3-Clause-Clear

pragma solidity >=0.8.13 <0.8.20;

import "../lib/TFHE.sol";

// Example use of optimistic ciphertext requires. Aims to show the different gas usage
// as compared to syncrhonous non-optimistic and plaintext ones.
contract OptimisticRequire {
    euint32 internal ct1;
    euint32 internal ct2;
    uint256 internal value;
    uint256 internal iterations;

    constructor() {}

    function init(bytes calldata ctBytes, uint256 _iterations) public {
        ct1 = TFHE.asEuint32(ctBytes);
        ct2 = TFHE.asEuint32(ctBytes);
        iterations = _iterations;
        value = 1;
    }

    function doWorkToPayGas() internal {
        uint256 newValue = value;
        for (uint256 i = 0; i < iterations; i++) {
            newValue += 2;
        }
        value = newValue;
    }

    function getValue() public view returns (uint256) {
        return value;
    }

    // Charge full gas as both requires are true.
    function optReqTrue() public {
        // True.
        TFHE.optReq(TFHE.le(ct1, ct2));

        // True.
        TFHE.optReq(TFHE.le(ct1, ct2));

        // Mutate state to pay for gas.
        doWorkToPayGas();
    }

    // Charge full gas as we are using optimistic requires.
    function optReqFalse() public {
        // True.
        TFHE.optReq(TFHE.le(ct1, ct2));

        // False.
        TFHE.optReq(TFHE.lt(ct1, ct2));

        // Mutate state to pay for gas - we will pay for it, because we are using optimistic requires.
        doWorkToPayGas();
    }

    // Charge less than full gas, because the non-optimistic ciphertext require aborts early.
    function reqFalse() public {
        // True.
        TFHE.req(TFHE.le(ct1, ct2));

        // False.
        TFHE.req(TFHE.lt(ct1, ct2));

        // Try to mutate state to pay for gas - we won't reach that point due to the false require.
        doWorkToPayGas();
    }

    // Must behave as reqFalse() in terms of gas.
    // Since gas estimation would always fail, call it without it by providing a gas value and observe transaction gas usage.
    function requireFalse() public {
        // False.
        require(false);

        // Try to mutate state to pay for gas - we won't reach that point due to the false require.
        doWorkToPayGas();
    }
}