convert method

@override Uint8List convert(String input)

An exception is thrown if input starts or ends with a space or has a character whose codeUnit is greater than 255.

Implementation

@override
Uint8List convert(String input) {
  if (input.isEmpty) {
    return Uint8List(0);
  }
  var psz = 0;

  /// Skip leading spaces.
  if (input[psz] == ' ') {
    throw ArgumentError.value(
        input, 'input', 'input cannot begin with a space.');
  }

  /// Skip and count leading '1's.
  var zeroes = 0;
  var length = 0;
  while (input.length > psz && input[psz] == alphabet[0]) {
    zeroes++;
    psz++;
  }

  /// Allocate enough space in big-endian base256 representation.
  var size = (((input.length - psz) * (log(alphabet.length) / log(256))) + 1)
      .toInt();
  var b256 = Uint8List(size);

  /// Process the characters.
  while (psz < input.length && input[psz].isNotEmpty) {
    /// Decode character
    var carry = _baseMap[input[psz].codeUnitAt(0)];

    /// Invalid character
    if (carry == 255) {
      throw ArgumentError.value(input, 'input',
          'The character "${input[psz]}" at index $psz is invalid.');
    }
    var i = 0;
    for (var it3 = size - 1;
        (carry != 0 || i < length) && (it3 != -1);
        it3--, i++) {
      carry += (alphabet.length * b256[it3]);
      b256[it3] = (carry % 256);
      carry = (carry ~/ 256);
    }
    if (carry != 0) {
      throw FormatException('Non-zero carry');
    }
    length = i;
    psz++;
  }

  /// Skip trailing spaces.
  if (psz < input.length && input[psz] == ' ') {
    throw ArgumentError.value(
        input, 'input', 'input cannot end with a space.');
  }

  /// Skip leading zeroes in b256.
  var it4 = size - length;
  while (it4 != size && b256[it4] == 0) {
    it4++;
  }
  var vch = Uint8List(zeroes + (size - it4));
  if (zeroes != 0) {
    vch.fillRange(0, zeroes, 0x00);
  }
  var j = zeroes;
  while (it4 != size) {
    vch[j++] = b256[it4++];
  }
  return vch;
}