Assembler Tricks & Tips

Optimizations

A fast way to clear the screen. If your assembler does not like the first instruction, just remove the ".w".

ClearScreen:
	lea 	$4440.W,a6
	movem.l	empty(pc),d1-d7/a0-a5	;Put zeros in registers
	moveq	#(128*30/52)-1,d0	;Clear as much as we can of our 128 lines
\loop:	movem.l	d1-d7/a0-a6,(a7)+	;Clear 52 bytes in x cycles
	dbf 	d0,\loop
	movem.l d1-d7/a0-a3,(a6)+	;Clear remaining bytes (depends on above)
	rts
empty:
	dcb.l	13,0

The (propably) fastest way to clear the screen. The REPT-ENDR statement below is not widely implemented in 68k-assemblers, but simply means to assemble the code between the keywords several times (64 in our case). Just cut & paste in the sourcecode instead.

ClearScreen:
	move.w	#$2700,SR
	move.l	a7,save
	lea	$4440.w,a7
	movem.l	Empty(pc),d0-d7/a0-a6
	REPT	64
	movem.l	d0-d7/a0-a6,(a7)+
	ENDR
	move.l	save(pc),a7
	move.w	#$2000,SR
	rts
save:	dc.l	0
empty:	dcb.l	15,0

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