Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!tcdcs!swift.cs.tcd.ie!vax1.tcd.ie!smcgerty
From: smcgerty@vax1.tcd.ie
Newsgroups: comp.sys.amiga.programmer
Subject: New life for MOVEM!
Message-ID: <1991Feb11.160212.7749@vax1.tcd.ie>
Date: 11 Feb 91 16:02:12 GMT
Organization: Trinity College Dublin
Lines: 41

Hi 68000 users!

Here's a little trick that someone might find useful:
(maybe its common knowlage?)

Right, picture the problem; you want to move, say, 1200 bytes from A to B
QUICKLY but you couldn't be bothered getting the Blitter to do it/Blitter is
busy/You just don't know how to get the blitter to do it.

So you do it like this

	LEA	Source,A0
	LEA	Dest,A1
	MOVE.W	#300,D0   ; 1200 Bs=300 LWs
Loop:   MOVE.L  (A0)+,(A1)+
	DBRA	D0,Loop

How about this, which takes about 2/3 of the time of the above:

	LEA	Source,A0
	LEA	Dest,A1
	MOVE.W	#25,D0             ;25*48=1200 bytes
Loop:	MOVEM.L (A0)+,D1-D7/A2-A6  ;12 LWs! = 48 bytes
	MOVEM.L D1-D7/A2-A6,(A1)
	ADDA.L	#48,A1        ;since MOVEM can't have (A1)+ as Dest. operand	
        DBRA	D0,Loop

Ok, so its a little register intensive, but you can always save all the regs
before using the routine, and restore them later.

Just to get a bit more speed, you could have a bigger loop, which has, say,
five itterations of the original loop in one loop, which saves you 4 DBRA
instructions for every 5-itteration. (I think thats almost 40 clock cycles!)
You may think thats trivial, but it all mounts up!

Anyone got any other tricks?

----------------------------------------------------------------------------
|  / T | /  Stephen John McGerty           |                     Amiga  // |
|  / | |/   smcgerty@vax1.tcd.ie (C.Sci.)  | "Hmm.. No, nothing."    \\//  |
|__________________________________________|_______________________________|