code: func encodeAlphanumericCharacter(v byte) uint32 {
  	c := uint32(v)
  
  	switch {
  	case c >= '0' && c <= '9':
  		// 0-9 encoded as 0-9.
  		return c - '0'
  	case c >= 'A' && c <= 'Z':
  		// A-Z encoded as 10-35.
  		return c - 'A' + 10
  	case c == ' ':
  		return 36
  	case c == '$':
  		return 37
  	case c == '%':
  		return 38
  	case c == '*':
  		return 39
  	case c == '+':
  		return 40
  	case c == '-':
  		return 41
  	case c == '.':
  		return 42
  	case c == '/':
  		return 43
  	case c == ':':
  		return 44
  	default:
  		log.Panicf("encodeAlphanumericCharacter() with non alphanumeric char %v.", v)
  	}
  
  	return 0
  }
docs: // encodeAlphanumericChar returns the QR Code encoded value of v.
  //
  // v must be a QR Code defined alphanumeric character: 0-9, A-Z, SP, $%*+-./ or
  // :. The characters are mapped to values in the range 0-44 respectively.