IFDIF            Assemble If Arguments Differ                  MASM Directive

IFDIF ,
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.

See also: IFIDN

IFDIF Assemble If Arguments Differ