@transmute/jose-ld/src/encoding/base-x.ts

``` npm i @transmute/jose-ld@latest --save ```

// base-x encoding / decoding
// Copyright (c) 2018 base-x contributors
// Copyright (c) 2014-2018 The Bitcoin Core developers (base58.cpp)
// Distributed under the MIT software license, see the accompanying
// file LICENSE or http://www.opensource.org/licenses/mit-license.php.
// @ts-ignore

export function base(ALPHABET) {
  if (ALPHABET.length >= 255) {
    throw new TypeError('Alphabet too long');
  }
  var BASE_MAP = new Uint8Array(256);
  for (var j = 0; j < BASE_MAP.length; j++) {
    BASE_MAP[j] = 255;
  }
  for (var i = 0; i < ALPHABET.length; i++) {
    var x = ALPHABET.charAt(i);
    var xc = x.charCodeAt(0);
    if (BASE_MAP[xc] !== 255) {
      throw new TypeError(x + ' is ambiguous');
    }
    BASE_MAP[xc] = i;
  }
  var BASE = ALPHABET.length;
  var LEADER = ALPHABET.charAt(0);
  var FACTOR = Math.log(BASE) / Math.log(256); // log(BASE) / log(256), rounded up
  var iFACTOR = Math.log(256) / Math.log(BASE); // log(256) / log(BASE), rounded up
  function encode(source: any) {
    if (Array.isArray(source) || source instanceof Uint8Array) {
      source = Buffer.from(source);
    }
    if (!Buffer.isBuffer(source)) {
      throw new TypeError('Expected Buffer');
    }
    if (source.length === 0) {
      return '';
    }
    // Skip & count leading zeroes.
    var zeroes = 0;
    var length = 0;
    var pbegin = 0;
    var pend = source.length;
    while (pbegin !== pend && source[pbegin] === 0) {
      pbegin++;
      zeroes++;
    }
    // Allocate enough space in big-endian base58 representation.
    var size = ((pend - pbegin) * iFACTOR + 1) >>> 0;
    var b58 = new Uint8Array(size);
    // Process the bytes.
    while (pbegin !== pend) {
      var carry = source[pbegin];
      // Apply "b58 = b58 * 256 + ch".
      var i = 0;
      for (
        var it1 = size - 1;
        (carry !== 0 || i < length) && it1 !== -1;
        it1--, i++
      ) {
        carry += (256 * b58[it1]) >>> 0;
        b58[it1] = carry % BASE >>> 0;
        carry = (carry / BASE) >>> 0;
      }
      if (carry !== 0) {
        throw new Error('Non-zero carry');
      }
      length = i;
      pbegin++;
    }
    // Skip leading zeroes in base58 result.
    var it2 = size - length;
    while (it2 !== size && b58[it2] === 0) {
      it2++;
    }
    // Translate the result into a string.
    var str = LEADER.repeat(zeroes);
    for (; it2 < size; ++it2) {
      str += ALPHABET.charAt(b58[it2]);
    }
    return str;
  }
  function decodeUnsafe(source: any) {
    if (typeof source !== 'string') {
      throw new TypeError('Expected String');
    }
    if (source.length === 0) {
      return Buffer.alloc(0);
    }
    var psz = 0;
    // Skip leading spaces.
    if (source[psz] === ' ') {
      return;
    }
    // Skip and count leading '1's.
    var zeroes = 0;
    var length = 0;
    while (source[psz] === LEADER) {
      zeroes++;
      psz++;
    }
    // Allocate enough space in big-endian base256 representation.
    var size = ((source.length - psz) * FACTOR + 1) >>> 0; // log(58) / log(256), rounded up.
    var b256 = new Uint8Array(size);
    // Process the characters.
    while (source[psz]) {
      // Decode character
      var carry = BASE_MAP[source.charCodeAt(psz)];
      // Invalid character
      if (carry === 255) {
        return;
      }
      var i = 0;
      for (
        var it3 = size - 1;
        (carry !== 0 || i < length) && it3 !== -1;
        it3--, i++
      ) {
        carry += (BASE * b256[it3]) >>> 0;
        b256[it3] = carry % 256 >>> 0;
        carry = (carry / 256) >>> 0;
      }
      if (carry !== 0) {
        throw new Error('Non-zero carry');
      }
      length = i;
      psz++;
    }
    // Skip trailing spaces.
    if (source[psz] === ' ') {
      return;
    }
    // Skip leading zeroes in b256.
    var it4 = size - length;
    while (it4 !== size && b256[it4] === 0) {
      it4++;
    }
    var vch = Buffer.allocUnsafe(zeroes + (size - it4));
    vch.fill(0x00, 0, zeroes);
    var j = zeroes;
    while (it4 !== size) {
      vch[j++] = b256[it4++];
    }
    return vch;
  }
  function decode(string: string) {
    var buffer = decodeUnsafe(string);
    if (buffer) {
      return buffer;
    }
    throw new Error('Non-base' + BASE + ' character');
  }
  return {
    encode: encode,
    decodeUnsafe: decodeUnsafe,
    decode: decode,
  };
}