openzeppelin-contracts/contracts/utils/structs/BitMaps.sol

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (utils/structs/BitMaps.sol)
pragma solidity ^0.8.20;

/**
 * @dev Library for managing uint256 to bool mapping in a compact and efficient way, provided the keys are sequential.
 * Largely inspired by Uniswap's https://github.com/Uniswap/merkle-distributor/blob/master/contracts/MerkleDistributor.sol[merkle-distributor].
 *
 * BitMaps pack 256 booleans across each bit of a single 256-bit slot of `uint256` type.
 * Hence booleans corresponding to 256 _sequential_ indices would only consume a single slot,
 * unlike the regular `bool` which would consume an entire slot for a single value.
 *
 * This results in gas savings in two ways:
 *
 * - Setting a zero value to non-zero only once every 256 times
 * - Accessing the same warm slot for every 256 _sequential_ indices
 */
library BitMaps {
    struct BitMap {
        mapping(uint256 bucket => uint256) _data;
    }

    /**
     * @dev Returns whether the bit at `index` is set.
     */
    function get(BitMap storage bitmap, uint256 index) internal view returns (bool) {
        uint256 bucket = index >> 8;
        uint256 mask = 1 << (index & 0xff);
        return bitmap._data[bucket] & mask != 0;
    }

    /**
     * @dev Sets the bit at `index` to the boolean `value`.
     */
    function setTo(BitMap storage bitmap, uint256 index, bool value) internal {
        if (value) {
            set(bitmap, index);
        } else {
            unset(bitmap, index);
        }
    }

    /**
     * @dev Sets the bit at `index`.
     */
    function set(BitMap storage bitmap, uint256 index) internal {
        uint256 bucket = index >> 8;
        uint256 mask = 1 << (index & 0xff);
        bitmap._data[bucket] |= mask;
    }

    /**
     * @dev Unsets the bit at `index`.
     */
    function unset(BitMap storage bitmap, uint256 index) internal {
        uint256 bucket = index >> 8;
        uint256 mask = 1 << (index & 0xff);
        bitmap._data[bucket] &= ~mask;
    }
}