base64 encoder

contracts/Base64.sol

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