base64.sol

// SPDX-License-Identifier: MIT

/// @title Base64
/// @author Brecht Devos - <brecht@loopring.org>
/// @notice Provides a function for encoding some bytes in base64
library Base64 {
    string internal constant TABLE = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

    function encode(bytes memory data) internal pure returns (string memory) {
        if (data.length == 0) return '';

        // load the table into memory
        string memory table = TABLE;

        // multiply by 4/3 rounded up
        uint256 encodedLen = 4 * ((data.length + 2) / 3);

        // add some extra buffer at the end required for the writing
        string memory result = new string(encodedLen + 32);

        assembly {
        // set the actual output length
            mstore(result, encodedLen)

        // prepare the lookup table
            let tablePtr := add(table, 1)

        // input ptr
            let dataPtr := data
            let endPtr := add(dataPtr, mload(data))

        // result ptr, jump over length
            let resultPtr := add(result, 32)

        // run over the input, 3 bytes at a time
            for {} lt(dataPtr, endPtr) {}
            {
                dataPtr := add(dataPtr, 3)

            // read 3 bytes
                let input := mload(dataPtr)

            // write 4 characters
                mstore(resultPtr, shl(248, mload(add(tablePtr, and(shr(18, input), 0x3F)))))
                resultPtr := add(resultPtr, 1)
                mstore(resultPtr, shl(248, mload(add(tablePtr, and(shr(12, input), 0x3F)))))
                resultPtr := add(resultPtr, 1)
                mstore(resultPtr, shl(248, mload(add(tablePtr, and(shr( 6, input), 0x3F)))))
                resultPtr := add(resultPtr, 1)
                mstore(resultPtr, shl(248, mload(add(tablePtr, and(        input,  0x3F)))))
                resultPtr := add(resultPtr, 1)
            }

        // padding with '='
            switch mod(mload(data), 3)
            case 1 { mstore(sub(resultPtr, 2), shl(240, 0x3d3d)) }
            case 2 { mstore(sub(resultPtr, 1), shl(248, 0x3d)) }
        }

        return result;
    }
}