convertBits function

Implementation

List<int> convertBits(
    {required List<int> data,
    required int from,
    required int to,
    required bool pad}) {
  var acc = 0;
  var bits = 0;
  var result = <int>[];
  var maxv = (1 << to) - 1;

  data.forEach((v) {
    if (v < 0 || (v >> from) != 0) {
      throw Exception();
    }
    acc = (acc << from) | v;
    bits += from;
    while (bits >= to) {
      bits -= to;
      result.add((acc >> bits) & maxv);
    }
  });

  if (pad) {
    if (bits > 0) {
      result.add((acc << (to - bits)) & maxv);
    }
  } else if (bits >= from) {
    throw InvalidPadding('illegal zero padding');
  } else if (((acc << (to - bits)) & maxv) != 0) {
    throw InvalidPadding('non zero');
  }

  return result;
}