IFDIF            Assemble If Arguments Differ                  MASM Directive

  IFDIF <argument1>,<argument2>
  statements
  [ELSE
  statements]
  ENDIF

    Initiates a conditional block, causing assembly of statements up to
    the optional ELSE directive, provided the two arguments (which may be
    names, numbers, or expressions) do not match character for character
    (they are different).

       Notes:     The comparison is case-sensitive.

                  The angle brackets must be included and the 2 arguments
                  must be separated by a comma.

                  This directive is often used to test parameters passed
                  to macro definitions.