code: private static final int base64ValueOf (final char c) {
          if ('A' <= c && c <= 'Z') return c - 'A';
          if ('a' <= c && c <= 'z') return c - 'a' + 26;
          if ('0' <= c && c <= '9') return c - '0' + 52;
          if (c == '+') return 62;
          if (c == '/') return 63;
          throw new NumberFormatException();
      }
docs: Returns a character's value in Base64
  
  @param c a character that is assigned a value from 0 to 63 in Base64
  @throws NumberFormatException if the parameter is not a Base64 character
  @return the character's value in Base64