decode function

List<int> decode(String input)

Implementation

List<int> decode(String input) {
  if (input.isEmpty) {
    return <int>[];
  }

  var encodedInput = utf8.encode(input);
  var uintAlphabet = utf8.encode(ALPHABET);

  List<int?> INDEXES = List<int>.filled(128, -1);
  for (int i = 0; i < ALPHABET.length; i++) {
      INDEXES[uintAlphabet[i]] = i;
  }

  // Convert the base58-encoded ASCII chars to a base58 byte sequence (base58 digits).
  List<int> input58 = List<int>.filled(encodedInput.length, 0);
  for (int i = 0; i < encodedInput.length; ++i) {
    var c = encodedInput[i];
    var digit = c < 128 ? INDEXES[c]! : -1;
    if (digit < 0) {
      var buff = <int>[c];
      var invalidChar = utf8.decode(buff);
      throw new AddressFormatException(
          "Illegal character " + invalidChar + " at position " + i.toString());
    }
    input58[i] = digit;
  }

  // Count leading zeros.
  int zeros = 0;
  while (zeros < input58.length && input58[zeros] == 0) {
    ++zeros;
  }

  // Convert base-58 digits to base-256 digits.
  var decoded = List<int>.filled(encodedInput.length, 0);
  int outputStart = decoded.length;
  for (int inputStart = zeros; inputStart < input58.length;) {
    decoded[--outputStart] = divmod(input58, inputStart, 58, 256);
    if (input58[inputStart] == 0) {
      ++inputStart; // optimization - skip leading zeros
    }
  }

  // Ignore extra leading zeroes that were added during the calculation.
  while (outputStart < decoded.length && decoded[outputStart] == 0) {
    ++outputStart;
  }

  // Return decoded data (including original number of leading zeros).
  return decoded.sublist(outputStart - zeros, decoded.length);
}