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93 lines
3.5 KiB
Solidity
93 lines
3.5 KiB
Solidity
2 years ago
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// SPDX-License-Identifier: MIT
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// OpenZeppelin Contracts (last updated v4.7.0) (utils/Base64.sol)
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pragma solidity ^0.8.0;
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/**
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* @dev Provides a set of functions to operate with Base64 strings.
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*
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* _Available since v4.5._
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*/
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library Base64 {
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/**
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* @dev Base64 Encoding/Decoding Table
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*/
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string internal constant _TABLE = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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/**
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* @dev Converts a `bytes` to its Bytes64 `string` representation.
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*/
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function encode(bytes memory data) internal pure returns (string memory) {
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/**
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* Inspired by Brecht Devos (Brechtpd) implementation - MIT licence
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* https://github.com/Brechtpd/base64/blob/e78d9fd951e7b0977ddca77d92dc85183770daf4/base64.sol
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*/
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if (data.length == 0) return "";
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// Loads the table into memory
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string memory table = _TABLE;
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// Encoding takes 3 bytes chunks of binary data from `bytes` data parameter
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// and split into 4 numbers of 6 bits.
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// The final Base64 length should be `bytes` data length multiplied by 4/3 rounded up
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// - `data.length + 2` -> Round up
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// - `/ 3` -> Number of 3-bytes chunks
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// - `4 *` -> 4 characters for each chunk
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string memory result = new string(4 * ((data.length + 2) / 3));
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/// @solidity memory-safe-assembly
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assembly {
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// Prepare the lookup table (skip the first "length" byte)
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let tablePtr := add(table, 1)
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// Prepare result pointer, jump over length
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let resultPtr := add(result, 32)
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// Run over the input, 3 bytes at a time
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for {
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let dataPtr := data
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let endPtr := add(data, mload(data))
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} lt(dataPtr, endPtr) {
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} {
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// Advance 3 bytes
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dataPtr := add(dataPtr, 3)
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let input := mload(dataPtr)
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// To write each character, shift the 3 bytes (18 bits) chunk
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// 4 times in blocks of 6 bits for each character (18, 12, 6, 0)
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// and apply logical AND with 0x3F which is the number of
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// the previous character in the ASCII table prior to the Base64 Table
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// The result is then added to the table to get the character to write,
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// and finally write it in the result pointer but with a left shift
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// of 256 (1 byte) - 8 (1 ASCII char) = 248 bits
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mstore8(resultPtr, mload(add(tablePtr, and(shr(18, input), 0x3F))))
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resultPtr := add(resultPtr, 1) // Advance
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mstore8(resultPtr, mload(add(tablePtr, and(shr(12, input), 0x3F))))
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resultPtr := add(resultPtr, 1) // Advance
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mstore8(resultPtr, mload(add(tablePtr, and(shr(6, input), 0x3F))))
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resultPtr := add(resultPtr, 1) // Advance
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mstore8(resultPtr, mload(add(tablePtr, and(input, 0x3F))))
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resultPtr := add(resultPtr, 1) // Advance
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}
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// When data `bytes` is not exactly 3 bytes long
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// it is padded with `=` characters at the end
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switch mod(mload(data), 3)
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case 1 {
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mstore8(sub(resultPtr, 1), 0x3d)
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mstore8(sub(resultPtr, 2), 0x3d)
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}
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case 2 {
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mstore8(sub(resultPtr, 1), 0x3d)
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}
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}
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return result;
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}
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}
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