This small gem show how to write code like:

        IF X=A AND Y=B THEN
	   { do something }
	ELSE
	   { do something else }
	END IF

In the gem presented the ELSE ... ENDIF statement may be skipped. If you have a branch predicting CPU the optimal way maybe to combine the two compares into a single conditional jump:


	mov     eax,a
	mov     ebx,b
	xor     eax,x           ; EAX = 0 if x = a
	xor     ebx,y           ; EBX = 0 if y = b
	or      eax,ebx         ; EAX = 0 if x = a and y = b
	jnz     short else      ; Jump if not 0
then:
		; do this...
	jmp     short endif
else:
		; do that...
endif:

You can use the same gem on 16 bit machines too, just use 16 bit registers instead.

Gem writer: Vesa Karvonen
last updated: 1998-03-16