IFIDN            Assemble If Arguments Are Identical           MASM Directive

IFIDN ,
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) match character for character.

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: IFDIF

IFIDN Assemble If Arguments Are Identical