code: private static byte convertHexDigit( final byte b )
      {
          if ( ( b >= '0' ) && ( b <= '9' ) )
          {
              return (byte) ( b - '0' );
          }
          if ( ( b >= 'a' ) && ( b <= 'f' ) )
          {
              return (byte) ( b - 'a' + 10 );
          }
          if ( ( b >= 'A' ) && ( b <= 'F' ) )
          {
              return (byte) ( b - 'A' + 10 );
          }
          return 0;
      }
docs: Convert a byte character value to hexidecimal digit value.
  
  @param b
  the character value byte