code: func fromHexChar(c byte) (byte, bool) {
  	switch {
  	case '0' <= c && c <= '9':
  		return c - '0', true
  	case 'a' <= c && c <= 'f':
  		return c - 'a' + 10, true
  	case 'A' <= c && c <= 'F':
  		return c - 'A' + 10, true
  	}
  
  	return 0, false
  }
docs: // fromHexChar converts a hex character into its value and a success flag.