String _convert()

in lib/src/hex/encoder.dart [55:90]

• 21 lines of code
• 7 McCabe index (conditional complexity)

String _convert(List<int> bytes, int start, int end) {
  // A Uint8List is more efficient than a StringBuffer given that we know that
  // we're only emitting ASCII-compatible characters, and that we know the
  // length ahead of time.
  var buffer = Uint8List((end - start) * 2);
  var bufferIndex = 0;

  // A bitwise OR of all bytes in [bytes]. This allows us to check for
  // out-of-range bytes without adding more branches than necessary to the
  // core loop.
  var byteOr = 0;
  for (var i = start; i < end; i++) {
    var byte = bytes[i];
    byteOr |= byte;

    // The bitwise arithmetic here is equivalent to `byte ~/ 16` and `byte % 16`
    // for valid byte values, but is easier for dart2js to optimize given that
    // it can't prove that [byte] will always be positive.
    buffer[bufferIndex++] = _codeUnitForDigit((byte & 0xF0) >> 4);
    buffer[bufferIndex++] = _codeUnitForDigit(byte & 0x0F);
  }

  if (byteOr >= 0 && byteOr <= 255) return String.fromCharCodes(buffer);

  // If there was an invalid byte, find it and throw an exception.
  for (var i = start; i < end; i++) {
    var byte = bytes[i];
    if (byte >= 0 && byte <= 0xff) continue;
    throw FormatException(
        "Invalid byte ${byte < 0 ? "-" : ""}0x${byte.abs().toRadixString(16)}.",
        bytes,
        i);
  }

  throw 'unreachable';
}