int _digitForByte()

in lib/src/chunked_coding/decoder.dart [154:179]

• 14 lines of code
• 5 McCabe index (conditional complexity)

  int _digitForByte(List<int> bytes, int index) {
    // If the byte is a numeral, get its value. XOR works because 0 in ASCII is
    // `0b110000` and the other numerals come after it in ascending order and
    // take up at most four bits.
    //
    // We check for digits first because it ensures there's only a single branch
    // for 10 out of 16 of the expected cases. We don't count the `digit >= 0`
    // check because branch prediction will always work on it for valid data.
    final byte = bytes[index];
    final digit = $0 ^ byte;
    if (digit <= 9) {
      if (digit >= 0) return digit;
    } else {
      // If the byte is an uppercase letter, convert it to lowercase. This works
      // because uppercase letters in ASCII are exactly `0b100000 = 0x20` less
      // than lowercase letters, so if we ensure that that bit is 1 we ensure
      // that the letter is lowercase.
      final letter = 0x20 | byte;
      if ($a <= letter && letter <= $f) return letter - $a + 10;
    }

    throw FormatException(
        'Invalid hexadecimal byte 0x${byte.toRadixString(16).toUpperCase()}.',
        bytes,
        index);
  }