@uzmoi/clockwork-base32/dist/decode.js

A fast and minimal implementation of Clockwork Base32 for TypeScript

import { encodeSymbols } from "./encode.js";
/**
 * Decode Clockwork Base32.
 *
 * @throws {RangeError} If byteOffset is invalid or the buffer is not long enough.
 * @throws {SyntaxError} If input contains invalid characters.
 *
 * @see https://gist.github.com/szktty/228f85794e4187882a77734c89c384a8
 */
export const decode = (string, buffer, byteOffset) => {
    const length = string.length * (5 / 8);
    const u8array = buffer == null
        ? new Uint8Array(length)
        : new Uint8Array(buffer, byteOffset, length);
    let index = 0;
    let state = 0;
    let offset = 0;
    for (let i = 0; i < string.length; i++) {
        const u5 = decodeSymbolMap[string.charCodeAt(i)];
        if (u5 === undefined || u5 === 0xff) {
            throw new SyntaxError(`'${string[i]}' is an invalid character in Clockwork Base32`);
        }
        offset += 5;
        state = (state << 5) | u5;
        if (offset >= 8) {
            offset -= 8;
            u8array[index++] = state >> offset;
        }
    }
    return u8array;
};
const decodeSymbolMap = new Uint8Array(0x80).fill(0xff);
decodeSymbolMap[0x4F] = decodeSymbolMap[0x6F] = 0; // O
decodeSymbolMap[0x49] = decodeSymbolMap[0x69] = 1; // I
decodeSymbolMap[0x4C] = decodeSymbolMap[0x6C] = 1; // L
for (let i = 0; i < encodeSymbols.length; i++) {
    const code = encodeSymbols[i].charCodeAt(0);
    decodeSymbolMap[code] = i;
    // is upper alphabet
    if (0x40 < code) {
        // to lower alphabet
        decodeSymbolMap[code + 0x20] = i;
    }
}