Casting Pointers - (nf)

grunwald at uiuccsb.UUCP grunwald at uiuccsb.UUCP
Sat Feb 4 13:43:11 AEST 1984

uiuccsb!grunwald    Feb  3 11:32:00 1984

If you want to generate a fast, non-portable copy for the 68000, include the
following lines as your copy routine:

register char	*from,		/* a5 */
		*to;		/* a4 */
register int	length;		/* d7 */
 *	only handles even byte boundries

	if (((int)from & 1 == 0) && ((int)to & 1 == 0)) {
	    asm("lplbl:	movl	a5 at ++,a4 at ++");
	    asm("	dbnz	d7,lplbl");
	else do_it_yourself;

This generates the following using the MIT CC68. I assume that ints are 32
bits, otherwise you might need to cast the pointer to a long. If you're going
to write machine dependent code, you might as well do it so that its as fast
as possible. While I'm not one to push the use of really kludgy things like
the "asm" construct, I think that when you're doing what you are trying to
do, it's useful.
   In the 68010 (e.g. as in the new Sun stations), there is a two word buffer
that was specificially designed for instruction pairs like the above. You
don't do any fetching for the opcoodes and the speed improvement is pretty
good. Check out the 68010 instruction manual for more details. However, if
you don't use the MIT CC68 compiler, you better try running the above
through cc -S whatever.c and look at the register allocations, etc.

	.globl	copy
	link	a6,#-_F1
	moveml	#_S1,a6@(-_F1)
	movl	a6@(8),a5
	movl	a6@(12),a4
	movl	a6@(16),d7
| A1 = 20
	movl	a5,d0
	andl	#1,d0
	bne	.L13
	movl	a4,d0
	andl	#0,d0
	beq	.L13
lplbl:	movl	a5 at ++,a4 at ++
		dbnz	d7,lplbl
	bra	.L12
.L12:	moveml	a6@(-_F1),#12416
	unlk	a6
_F1 = 12
_S1 = 12416
| M1 = 0

Dirk Grunwald
University of Illinois
... ! ihnp4 ! uiucdcs ! grunwald

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