openzeppelin-contracts/contracts/governance/Governor.sol

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.1) (governance/Governor.sol)

pragma solidity ^0.8.19;

import {IERC721Receiver} from "../token/ERC721/IERC721Receiver.sol";
import {IERC1155Receiver} from "../token/ERC1155/IERC1155Receiver.sol";
import {EIP712} from "../utils/cryptography/EIP712.sol";
import {SignatureChecker} from "../utils/cryptography/SignatureChecker.sol";
import {IERC165, ERC165} from "../utils/introspection/ERC165.sol";
import {SafeCast} from "../utils/math/SafeCast.sol";
import {DoubleEndedQueue} from "../utils/structs/DoubleEndedQueue.sol";
import {Address} from "../utils/Address.sol";
import {Context} from "../utils/Context.sol";
import {Nonces} from "../utils/Nonces.sol";
import {IGovernor, IERC6372} from "./IGovernor.sol";

/**
 * @dev Core of the governance system, designed to be extended though various modules.
 *
 * This contract is abstract and requires several functions to be implemented in various modules:
 *
 * - A counting module must implement {quorum}, {_quorumReached}, {_voteSucceeded} and {_countVote}
 * - A voting module must implement {_getVotes}
 * - Additionally, {votingPeriod} must also be implemented
 *
 * _Available since v4.3._
 */
abstract contract Governor is Context, ERC165, EIP712, Nonces, IGovernor, IERC721Receiver, IERC1155Receiver {
    using DoubleEndedQueue for DoubleEndedQueue.Bytes32Deque;

    bytes32 public constant BALLOT_TYPEHASH =
        keccak256("Ballot(uint256 proposalId,uint8 support,address voter,uint256 nonce)");
    bytes32 public constant EXTENDED_BALLOT_TYPEHASH =
        keccak256(
            "ExtendedBallot(uint256 proposalId,uint8 support,address voter,uint256 nonce,string reason,bytes params)"
        );

    // solhint-disable var-name-mixedcase
    struct ProposalCore {
        address proposer;
        uint48 voteStart;
        uint32 voteDuration;
        bool executed;
        bool canceled;
    }
    // solhint-enable var-name-mixedcase

    bytes32 private constant _ALL_PROPOSAL_STATES_BITMAP = bytes32((2 ** (uint8(type(ProposalState).max) + 1)) - 1);
    string private _name;

    mapping(uint256 => ProposalCore) private _proposals;

    // This queue keeps track of the governor operating on itself. Calls to functions protected by the
    // {onlyGovernance} modifier needs to be whitelisted in this queue. Whitelisting is set in {_beforeExecute},
    // consumed by the {onlyGovernance} modifier and eventually reset in {_afterExecute}. This ensures that the
    // execution of {onlyGovernance} protected calls can only be achieved through successful proposals.
    DoubleEndedQueue.Bytes32Deque private _governanceCall;

    /**
     * @dev Restricts a function so it can only be executed through governance proposals. For example, governance
     * parameter setters in {GovernorSettings} are protected using this modifier.
     *
     * The governance executing address may be different from the Governor's own address, for example it could be a
     * timelock. This can be customized by modules by overriding {_executor}. The executor is only able to invoke these
     * functions during the execution of the governor's {execute} function, and not under any other circumstances. Thus,
     * for example, additional timelock proposers are not able to change governance parameters without going through the
     * governance protocol (since v4.6).
     */
    modifier onlyGovernance() {
        if (_executor() != _msgSender()) {
            revert GovernorOnlyExecutor(_msgSender());
        }
        if (_executor() != address(this)) {
            bytes32 msgDataHash = keccak256(_msgData());
            // loop until popping the expected operation - throw if deque is empty (operation not authorized)
            while (_governanceCall.popFront() != msgDataHash) {}
        }
        _;
    }

    /**
     * @dev Sets the value for {name} and {version}
     */
    constructor(string memory name_) EIP712(name_, version()) {
        _name = name_;
    }

    /**
     * @dev Function to receive ETH that will be handled by the governor (disabled if executor is a third party contract)
     */
    receive() external payable virtual {
        if (_executor() != address(this)) {
            revert GovernorDisabledDeposit();
        }
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC165) returns (bool) {
        bytes4 governorCancelId = this.cancel.selector ^ this.proposalProposer.selector;

        bytes4 governorParamsId = this.castVoteWithReasonAndParams.selector ^
            this.castVoteWithReasonAndParamsBySig.selector ^
            this.getVotesWithParams.selector;

        // The original interface id in v4.3.
        bytes4 governor43Id = type(IGovernor).interfaceId ^
            type(IERC6372).interfaceId ^
            governorCancelId ^
            governorParamsId;

        // An updated interface id in v4.6, with params added.
        bytes4 governor46Id = type(IGovernor).interfaceId ^ type(IERC6372).interfaceId ^ governorCancelId;

        // For the updated interface id in v4.9, we use governorCancelId directly.

        return
            interfaceId == governor43Id ||
            interfaceId == governor46Id ||
            interfaceId == governorCancelId ||
            interfaceId == type(IERC1155Receiver).interfaceId ||
            super.supportsInterface(interfaceId);
    }

    /**
     * @dev See {IGovernor-name}.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IGovernor-version}.
     */
    function version() public view virtual override returns (string memory) {
        return "1";
    }

    /**
     * @dev See {IGovernor-hashProposal}.
     *
     * The proposal id is produced by hashing the ABI encoded `targets` array, the `values` array, the `calldatas` array
     * and the descriptionHash (bytes32 which itself is the keccak256 hash of the description string). This proposal id
     * can be produced from the proposal data which is part of the {ProposalCreated} event. It can even be computed in
     * advance, before the proposal is submitted.
     *
     * Note that the chainId and the governor address are not part of the proposal id computation. Consequently, the
     * same proposal (with same operation and same description) will have the same id if submitted on multiple governors
     * across multiple networks. This also means that in order to execute the same operation twice (on the same
     * governor) the proposer will have to change the description in order to avoid proposal id conflicts.
     */
    function hashProposal(
        address[] memory targets,
        uint256[] memory values,
        bytes[] memory calldatas,
        bytes32 descriptionHash
    ) public pure virtual override returns (uint256) {
        return uint256(keccak256(abi.encode(targets, values, calldatas, descriptionHash)));
    }

    /**
     * @dev See {IGovernor-state}.
     */
    function state(uint256 proposalId) public view virtual override returns (ProposalState) {
        // ProposalCore is just one slot. We can load it from storage to memory with a single sload and use memory
        // object as a cache. This avoid duplicating expensive sloads.
        ProposalCore memory proposal = _proposals[proposalId];

        if (proposal.executed) {
            return ProposalState.Executed;
        }

        if (proposal.canceled) {
            return ProposalState.Canceled;
        }

        uint256 snapshot = proposalSnapshot(proposalId);

        if (snapshot == 0) {
            revert GovernorNonexistentProposal(proposalId);
        }

        uint256 currentTimepoint = clock();

        if (snapshot >= currentTimepoint) {
            return ProposalState.Pending;
        }

        uint256 deadline = proposalDeadline(proposalId);

        if (deadline >= currentTimepoint) {
            return ProposalState.Active;
        }

        if (_quorumReached(proposalId) && _voteSucceeded(proposalId)) {
            return ProposalState.Succeeded;
        } else {
            return ProposalState.Defeated;
        }
    }

    /**
     * @dev Part of the Governor Bravo's interface: _"The number of votes required in order for a voter to become a proposer"_.
     */
    function proposalThreshold() public view virtual returns (uint256) {
        return 0;
    }

    /**
     * @dev See {IGovernor-proposalSnapshot}.
     */
    function proposalSnapshot(uint256 proposalId) public view virtual override returns (uint256) {
        return _proposals[proposalId].voteStart;
    }

    /**
     * @dev See {IGovernor-proposalDeadline}.
     */
    function proposalDeadline(uint256 proposalId) public view virtual override returns (uint256) {
        return _proposals[proposalId].voteStart + _proposals[proposalId].voteDuration;
    }

    /**
     * @dev Returns the account that created a given proposal.
     */
    function proposalProposer(uint256 proposalId) public view virtual override returns (address) {
        return _proposals[proposalId].proposer;
    }

    /**
     * @dev Amount of votes already cast passes the threshold limit.
     */
    function _quorumReached(uint256 proposalId) internal view virtual returns (bool);

    /**
     * @dev Is the proposal successful or not.
     */
    function _voteSucceeded(uint256 proposalId) internal view virtual returns (bool);

    /**
     * @dev Get the voting weight of `account` at a specific `timepoint`, for a vote as described by `params`.
     */
    function _getVotes(address account, uint256 timepoint, bytes memory params) internal view virtual returns (uint256);

    /**
     * @dev Register a vote for `proposalId` by `account` with a given `support`, voting `weight` and voting `params`.
     *
     * Note: Support is generic and can represent various things depending on the voting system used.
     */
    function _countVote(
        uint256 proposalId,
        address account,
        uint8 support,
        uint256 weight,
        bytes memory params
    ) internal virtual;

    /**
     * @dev Default additional encoded parameters used by castVote methods that don't include them
     *
     * Note: Should be overridden by specific implementations to use an appropriate value, the
     * meaning of the additional params, in the context of that implementation
     */
    function _defaultParams() internal view virtual returns (bytes memory) {
        return "";
    }

    /**
     * @dev See {IGovernor-propose}. This function has opt-in frontrunning protection, described in {_isValidDescriptionForProposer}.
     */
    function propose(
        address[] memory targets,
        uint256[] memory values,
        bytes[] memory calldatas,
        string memory description
    ) public virtual override returns (uint256) {
        address proposer = _msgSender();
        require(_isValidDescriptionForProposer(proposer, description), "Governor: proposer restricted");

        uint256 currentTimepoint = clock();

        // Avoid stack too deep
        {
            uint256 proposerVotes = getVotes(proposer, currentTimepoint - 1);
            uint256 votesThreshold = proposalThreshold();
            if (proposerVotes < votesThreshold) {
                revert GovernorInsufficientProposerVotes(proposer, proposerVotes, votesThreshold);
            }
        }

        uint256 proposalId = hashProposal(targets, values, calldatas, keccak256(bytes(description)));

        if (targets.length != values.length || targets.length != calldatas.length || targets.length == 0) {
            revert GovernorInvalidProposalLength(targets.length, calldatas.length, values.length);
        }
        if (_proposals[proposalId].voteStart != 0) {
            revert GovernorUnexpectedProposalState(proposalId, state(proposalId), bytes32(0));
        }

        uint256 snapshot = currentTimepoint + votingDelay();
        uint256 duration = votingPeriod();

        _proposals[proposalId] = ProposalCore({
            proposer: proposer,
            voteStart: SafeCast.toUint48(snapshot),
            voteDuration: SafeCast.toUint32(duration),
            executed: false,
            canceled: false
        });

        emit ProposalCreated(
            proposalId,
            proposer,
            targets,
            values,
            new string[](targets.length),
            calldatas,
            snapshot,
            snapshot + duration,
            description
        );

        return proposalId;
    }

    /**
     * @dev See {IGovernor-execute}.
     */
    function execute(
        address[] memory targets,
        uint256[] memory values,
        bytes[] memory calldatas,
        bytes32 descriptionHash
    ) public payable virtual override returns (uint256) {
        uint256 proposalId = hashProposal(targets, values, calldatas, descriptionHash);

        ProposalState currentState = state(proposalId);
        if (currentState != ProposalState.Succeeded && currentState != ProposalState.Queued) {
            revert GovernorUnexpectedProposalState(
                proposalId,
                currentState,
                _encodeStateBitmap(ProposalState.Succeeded) | _encodeStateBitmap(ProposalState.Queued)
            );
        }
        _proposals[proposalId].executed = true;

        emit ProposalExecuted(proposalId);

        _beforeExecute(proposalId, targets, values, calldatas, descriptionHash);
        _execute(proposalId, targets, values, calldatas, descriptionHash);
        _afterExecute(proposalId, targets, values, calldatas, descriptionHash);

        return proposalId;
    }

    /**
     * @dev See {IGovernor-cancel}.
     */
    function cancel(
        address[] memory targets,
        uint256[] memory values,
        bytes[] memory calldatas,
        bytes32 descriptionHash
    ) public virtual override returns (uint256) {
        uint256 proposalId = hashProposal(targets, values, calldatas, descriptionHash);
        ProposalState currentState = state(proposalId);
        if (currentState != ProposalState.Pending) {
            revert GovernorUnexpectedProposalState(proposalId, currentState, _encodeStateBitmap(ProposalState.Pending));
        }
        if (_msgSender() != proposalProposer(proposalId)) {
            revert GovernorOnlyProposer(_msgSender());
        }
        return _cancel(targets, values, calldatas, descriptionHash);
    }

    /**
     * @dev Internal execution mechanism. Can be overridden to implement different execution mechanism
     */
    function _execute(
        uint256 /* proposalId */,
        address[] memory targets,
        uint256[] memory values,
        bytes[] memory calldatas,
        bytes32 /*descriptionHash*/
    ) internal virtual {
        for (uint256 i = 0; i < targets.length; ++i) {
            (bool success, bytes memory returndata) = targets[i].call{value: values[i]}(calldatas[i]);
            Address.verifyCallResult(success, returndata);
        }
    }

    /**
     * @dev Hook before execution is triggered.
     */
    function _beforeExecute(
        uint256 /* proposalId */,
        address[] memory targets,
        uint256[] memory /* values */,
        bytes[] memory calldatas,
        bytes32 /*descriptionHash*/
    ) internal virtual {
        if (_executor() != address(this)) {
            for (uint256 i = 0; i < targets.length; ++i) {
                if (targets[i] == address(this)) {
                    _governanceCall.pushBack(keccak256(calldatas[i]));
                }
            }
        }
    }

    /**
     * @dev Hook after execution is triggered.
     */
    function _afterExecute(
        uint256 /* proposalId */,
        address[] memory /* targets */,
        uint256[] memory /* values */,
        bytes[] memory /* calldatas */,
        bytes32 /*descriptionHash*/
    ) internal virtual {
        if (_executor() != address(this)) {
            if (!_governanceCall.empty()) {
                _governanceCall.clear();
            }
        }
    }

    /**
     * @dev Internal cancel mechanism: locks up the proposal timer, preventing it from being re-submitted. Marks it as
     * canceled to allow distinguishing it from executed proposals.
     *
     * Emits a {IGovernor-ProposalCanceled} event.
     */
    function _cancel(
        address[] memory targets,
        uint256[] memory values,
        bytes[] memory calldatas,
        bytes32 descriptionHash
    ) internal virtual returns (uint256) {
        uint256 proposalId = hashProposal(targets, values, calldatas, descriptionHash);

        ProposalState currentState = state(proposalId);

        bytes32 forbiddenStates = _encodeStateBitmap(ProposalState.Canceled) |
            _encodeStateBitmap(ProposalState.Expired) |
            _encodeStateBitmap(ProposalState.Executed);
        if (forbiddenStates & _encodeStateBitmap(currentState) != 0) {
            revert GovernorUnexpectedProposalState(
                proposalId,
                currentState,
                _ALL_PROPOSAL_STATES_BITMAP ^ forbiddenStates
            );
        }
        _proposals[proposalId].canceled = true;

        emit ProposalCanceled(proposalId);

        return proposalId;
    }

    /**
     * @dev See {IGovernor-getVotes}.
     */
    function getVotes(address account, uint256 timepoint) public view virtual override returns (uint256) {
        return _getVotes(account, timepoint, _defaultParams());
    }

    /**
     * @dev See {IGovernor-getVotesWithParams}.
     */
    function getVotesWithParams(
        address account,
        uint256 timepoint,
        bytes memory params
    ) public view virtual override returns (uint256) {
        return _getVotes(account, timepoint, params);
    }

    /**
     * @dev See {IGovernor-castVote}.
     */
    function castVote(uint256 proposalId, uint8 support) public virtual override returns (uint256) {
        address voter = _msgSender();
        return _castVote(proposalId, voter, support, "");
    }

    /**
     * @dev See {IGovernor-castVoteWithReason}.
     */
    function castVoteWithReason(
        uint256 proposalId,
        uint8 support,
        string calldata reason
    ) public virtual override returns (uint256) {
        address voter = _msgSender();
        return _castVote(proposalId, voter, support, reason);
    }

    /**
     * @dev See {IGovernor-castVoteWithReasonAndParams}.
     */
    function castVoteWithReasonAndParams(
        uint256 proposalId,
        uint8 support,
        string calldata reason,
        bytes memory params
    ) public virtual override returns (uint256) {
        address voter = _msgSender();
        return _castVote(proposalId, voter, support, reason, params);
    }

    /**
     * @dev See {IGovernor-castVoteBySig}.
     */
    function castVoteBySig(
        uint256 proposalId,
        uint8 support,
        address voter,
        bytes memory signature
    ) public virtual override returns (uint256) {
        bool valid = SignatureChecker.isValidSignatureNow(
            voter,
            _hashTypedDataV4(keccak256(abi.encode(BALLOT_TYPEHASH, proposalId, support, voter, _useNonce(voter)))),
            signature
        );

        if (!valid) {
            revert GovernorInvalidSignature(voter);
        }

        return _castVote(proposalId, voter, support, "");
    }

    /**
     * @dev See {IGovernor-castVoteWithReasonAndParamsBySig}.
     */
    function castVoteWithReasonAndParamsBySig(
        uint256 proposalId,
        uint8 support,
        address voter,
        string calldata reason,
        bytes memory params,
        bytes memory signature
    ) public virtual override returns (uint256) {
        bool valid = SignatureChecker.isValidSignatureNow(
            voter,
            _hashTypedDataV4(
                keccak256(
                    abi.encode(
                        EXTENDED_BALLOT_TYPEHASH,
                        proposalId,
                        support,
                        voter,
                        _useNonce(voter),
                        keccak256(bytes(reason)),
                        keccak256(params)
                    )
                )
            ),
            signature
        );

        if (!valid) {
            revert GovernorInvalidSignature(voter);
        }

        return _castVote(proposalId, voter, support, reason, params);
    }

    /**
     * @dev Internal vote casting mechanism: Check that the vote is pending, that it has not been cast yet, retrieve
     * voting weight using {IGovernor-getVotes} and call the {_countVote} internal function. Uses the _defaultParams().
     *
     * Emits a {IGovernor-VoteCast} event.
     */
    function _castVote(
        uint256 proposalId,
        address account,
        uint8 support,
        string memory reason
    ) internal virtual returns (uint256) {
        return _castVote(proposalId, account, support, reason, _defaultParams());
    }

    /**
     * @dev Internal vote casting mechanism: Check that the vote is pending, that it has not been cast yet, retrieve
     * voting weight using {IGovernor-getVotes} and call the {_countVote} internal function.
     *
     * Emits a {IGovernor-VoteCast} event.
     */
    function _castVote(
        uint256 proposalId,
        address account,
        uint8 support,
        string memory reason,
        bytes memory params
    ) internal virtual returns (uint256) {
        ProposalState currentState = state(proposalId);
        if (currentState != ProposalState.Active) {
            revert GovernorUnexpectedProposalState(proposalId, currentState, _encodeStateBitmap(ProposalState.Active));
        }

        uint256 weight = _getVotes(account, proposalSnapshot(proposalId), params);
        _countVote(proposalId, account, support, weight, params);

        if (params.length == 0) {
            emit VoteCast(account, proposalId, support, weight, reason);
        } else {
            emit VoteCastWithParams(account, proposalId, support, weight, reason, params);
        }

        return weight;
    }

    /**
     * @dev Relays a transaction or function call to an arbitrary target. In cases where the governance executor
     * is some contract other than the governor itself, like when using a timelock, this function can be invoked
     * in a governance proposal to recover tokens or Ether that was sent to the governor contract by mistake.
     * Note that if the executor is simply the governor itself, use of `relay` is redundant.
     */
    function relay(address target, uint256 value, bytes calldata data) external payable virtual onlyGovernance {
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        Address.verifyCallResult(success, returndata);
    }

    /**
     * @dev Address through which the governor executes action. Will be overloaded by module that execute actions
     * through another contract such as a timelock.
     */
    function _executor() internal view virtual returns (address) {
        return address(this);
    }

    /**
     * @dev See {IERC721Receiver-onERC721Received}.
     * Receiving tokens is disabled if the governance executor is other than the governor itself (eg. when using with a timelock).
     */
    function onERC721Received(address, address, uint256, bytes memory) public virtual returns (bytes4) {
        if (_executor() != address(this)) {
            revert GovernorDisabledDeposit();
        }
        return this.onERC721Received.selector;
    }

    /**
     * @dev See {IERC1155Receiver-onERC1155Received}.
     * Receiving tokens is disabled if the governance executor is other than the governor itself (eg. when using with a timelock).
     */
    function onERC1155Received(address, address, uint256, uint256, bytes memory) public virtual returns (bytes4) {
        if (_executor() != address(this)) {
            revert GovernorDisabledDeposit();
        }
        return this.onERC1155Received.selector;
    }

    /**
     * @dev See {IERC1155Receiver-onERC1155BatchReceived}.
     * Receiving tokens is disabled if the governance executor is other than the governor itself (eg. when using with a timelock).
     */
    function onERC1155BatchReceived(
        address,
        address,
        uint256[] memory,
        uint256[] memory,
        bytes memory
    ) public virtual returns (bytes4) {
        if (_executor() != address(this)) {
            revert GovernorDisabledDeposit();
        }
        return this.onERC1155BatchReceived.selector;
    }

    /**
     * @dev Encodes a `ProposalState` into a `bytes32` representation where each bit enabled corresponds to
     * the underlying position in the `ProposalState` enum. For example:
     *
     * 0x000...10000
     *   ^^^^^^------ ...
     *         ^----- Succeeded
     *          ^---- Defeated
     *           ^--- Canceled
     *            ^-- Active
     *             ^- Pending
     */
    function _encodeStateBitmap(ProposalState proposalState) internal pure returns (bytes32) {
        return bytes32(1 << uint8(proposalState));
    }

    /*
     * @dev Check if the proposer is authorized to submit a proposal with the given description.
     *
     * If the proposal description ends with `#proposer=0x???`, where `0x???` is an address written as a hex string
     * (case insensitive), then the submission of this proposal will only be authorized to said address.
     *
     * This is used for frontrunning protection. By adding this pattern at the end of their proposal, one can ensure
     * that no other address can submit the same proposal. An attacker would have to either remove or change that part,
     * which would result in a different proposal id.
     *
     * If the description does not match this pattern, it is unrestricted and anyone can submit it. This includes:
     * - If the `0x???` part is not a valid hex string.
     * - If the `0x???` part is a valid hex string, but does not contain exactly 40 hex digits.
     * - If it ends with the expected suffix followed by newlines or other whitespace.
     * - If it ends with some other similar suffix, e.g. `#other=abc`.
     * - If it does not end with any such suffix.
     */
    function _isValidDescriptionForProposer(
        address proposer,
        string memory description
    ) internal view virtual returns (bool) {
        uint256 len = bytes(description).length;

        // Length is too short to contain a valid proposer suffix
        if (len < 52) {
            return true;
        }

        // Extract what would be the `#proposer=0x` marker beginning the suffix
        bytes12 marker;
        assembly {
            // - Start of the string contents in memory = description + 32
            // - First character of the marker = len - 52
            //   - Length of "#proposer=0x0000000000000000000000000000000000000000" = 52
            // - We read the memory word starting at the first character of the marker:
            //   - (description + 32) + (len - 52) = description + (len - 20)
            // - Note: Solidity will ignore anything past the first 12 bytes
            marker := mload(add(description, sub(len, 20)))
        }

        // If the marker is not found, there is no proposer suffix to check
        if (marker != bytes12("#proposer=0x")) {
            return true;
        }

        // Parse the 40 characters following the marker as uint160
        uint160 recovered = 0;
        for (uint256 i = len - 40; i < len; ++i) {
            (bool isHex, uint8 value) = _tryHexToUint(bytes(description)[i]);
            // If any of the characters is not a hex digit, ignore the suffix entirely
            if (!isHex) {
                return true;
            }
            recovered = (recovered << 4) | value;
        }

        return recovered == uint160(proposer);
    }

    /**
     * @dev Try to parse a character from a string as a hex value. Returns `(true, value)` if the char is in
     * `[0-9a-fA-F]` and `(false, 0)` otherwise. Value is guaranteed to be in the range `0 <= value < 16`
     */
    function _tryHexToUint(bytes1 char) private pure returns (bool, uint8) {
        uint8 c = uint8(char);
        unchecked {
            // Case 0-9
            if (47 < c && c < 58) {
                return (true, c - 48);
            }
            // Case A-F
            else if (64 < c && c < 71) {
                return (true, c - 55);
            }
            // Case a-f
            else if (96 < c && c < 103) {
                return (true, c - 87);
            }
            // Else: not a hex char
            else {
                return (false, 0);
            }
        }
    }
}