convert method

@override Uint8List convert(covariant List<int> input)

Converts input array of numbers with bit-length of source to an array of numbers with bit-length of target. The input array will be treated as a sequence of bits to convert.

After consuming all of input sequence, if there are some non-zero partial word remains, 0 will be padded on the right to make the final word.

Implementation

@override
Uint8List convert(List<int> input) {
  final table = alphabet;
  final pad = padding;
  final tb = target;
  final len = input.length;
  if (tb < 2 || tb > 64) {
    throw ArgumentError.value(target, 'target', 'should be between 2 to 64');
  }

  // number of output words = ceil(total input bits / tb)
  int n = len << 3;
  int outLen = (n + tb - 1) ~/ tb;
  if (pad != null) {
    final low = tb & -tb;
    final period = low < 8 ? 8 ~/ low : 1;
    outLen = ((outLen + period - 1) ~/ period) * period;
  }
  var out = Uint8List(outLen);

  // regroup the input bytes and map each word through the alphabet
  int i, p, l;
  p = n = l = 0;
  for (i = 0; i < len; ++i) {
    p = (p << 8) | (input[i] & 0xFF);
    n += 8;
    while (n >= tb) {
      n -= tb;
      out[l++] = table[p >>> n];
      p &= (1 << n) - 1;
    }
  }

  // if a partial word remains, left-align it, zero-padding the low bits
  if (n > 0) {
    out[l++] = table[p << (tb - n)];
  }

  // fill the remaining slots with the padding character
  if (pad != null) {
    while (l < outLen) {
      out[l++] = pad;
    }
  }

  return out;
}