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Old 27 February 2011, 21:51   #1
h0ffman
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help optimising a section of code

Hi guys..

can anyone help me optimise this section of code. It's part of my scope routine..

Code:
MOVEQ	#7,D3
	MOVE.B	(A0)+,D0	; get byte
	EXT.W	D0		; extend to word
	NEG.W	D0		; negate
	MULS	D5,D0		; multiply by volume
	ASR.W	#7,D0		; shift down
	MOVE.W	D0,D1
	ASL.W	#5,D0		; * 32
	ASL.W	#3,D1		; * 8
	ADD.W	D1,D0		; (32+8) = * 40
	BSET	D3,(A1,D0.W)	; set a bit
I've rolled it out of the loop and its running faster, but wondered if there was anything that could be done to speed up this process??

Cheers
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Old 27 February 2011, 22:14   #2
frank_b
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Is d5 a constant? If so and you're on a 68k use a look up table.
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Old 27 February 2011, 22:50   #3
h0ffman
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D5 is the volume. Min value coming in would be 1 and max would be 32.
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Old 28 February 2011, 00:20   #4
Kalms
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Then create 32 different lookup tables, one for each possible volume level. Both the multiply and those shifts are scary slow.
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Old 28 February 2011, 01:05   #5
StingRay
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What Kalms said. You can precalculate almost the complete innnerloop into a table (rows = volume, columns = byte), then it's just a matter of pointing to the right line in the table which you can do in the outer loop once the volume has been calculated. And in the innerloop you just read the value from the table depending on the sample byte and do the bset.
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Old 28 February 2011, 01:17   #6
h0ffman
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7530 bytes of pre-calc data..... hmmm.. think I has room for that...

Oh and thanks for that guys. As soon as you said rows / columns.. it all made sense.
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Old 28 February 2011, 05:26   #7
matthey
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Code:
    MOVE.B    (A0)+,D0    ; get byte
    EXTB.L    D0        ; extend to word
    NEG.L    D0        ; negate
    MULS    D5,D0        ; multiply by volume
    ASR.L    #4,D0        ; shift down
    MOVE.L    D0,D1
    ASL.L    #2,D0        ; * 32
    ADD.L    D1,D0        ; (32+8) = * 40
    ;stick an instruction that doesn't alter A1 or D0 here if possible
    BSET    #7,(A1,D0.L)    ; set a bit
Check this for correctness. It should be faster than before on 68020-68060. It makes a couple of assumptions though. MULS is going to be faster on 68060 than a lookup table. Use of long values makes the code almost twice as fast on the 68060. The (A1,D0.L) I believe is faster on 68020-68040 too. Immediate BSET is faster than adding MOVEQ.

Last edited by matthey; 28 February 2011 at 05:32.
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Old 28 February 2011, 10:25   #8
StingRay
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Quote:
Originally Posted by matthey View Post
Check this for correctness. It should be faster than before on 68020-68060. It makes a couple of assumptions though.
And one assumption is that he needs 020-060 optimised code. He needs the code optimised for 68000.
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Old 28 February 2011, 11:32   #9
h0ffman
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Well spotted stingray, yep runs fine on the 68020, plenty of raster time left. Its running it on the A600 thats where the issue is.. I think this lookup is going to pimp it right up Will let you guys know later how it's gone.
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Old 28 February 2011, 12:04   #10
StingRay
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I had a few seconds to spare at work, this table should do what you need. Since I don't want to spoil your fun coming up with a solution yourself, this is not the fully optimized version, i.e. I didn't precalc everything. The code should just give you an idea how to do it.

Code:
MAKETAB	lea	TAB(pc),a0
	moveq	#0,d0		; vol
.loop	moveq	#0,d1
.loopvol
	move.w	d1,d2
	ext.w	d2
	neg.w	d2
	muls.w	d0,d2
	asr.w	#7,d2
	move.w	d2,(a0)+
	addq.b	#1,d1
	bcc.b	.loopvol
	addq.b	#1,d0
	cmp.b	#32,d0
	blt.b	.loop
	rts

TAB	ds.w	32*256		; vol -> byte
Edit:
Quote:
Originally Posted by h0ffman View Post
7530 bytes of pre-calc data..... hmmm.. think I has room for that...
How did you calculate that number?

Last edited by StingRay; 28 February 2011 at 12:10.
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Old 28 February 2011, 16:10   #11
h0ffman
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wrongly as i found out today!

anyways, got it in, f@*k me thats quicker! Still a lot to do on it like ensuring it draws loops correctly etc... but getting there

Cheers again
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Old 28 February 2011, 16:16   #12
pmc
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Quote:
Originally Posted by h0ffman
anyways, got it in, f@*k me thats quicker!
LOL.

True though, on 68000, the LUT is your friend
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Old 28 February 2011, 16:22   #13
h0ffman
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Once i've finished it, i'll send it over mate
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Old 28 February 2011, 16:24   #14
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\o/
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Old 02 March 2011, 08:16   #15
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That snippet on the first page is actually from the ProTracker source code.. :P
/me has been reading PT1.2.asm too much!
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Old 02 March 2011, 14:19   #16
h0ffman
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Well spotted fella. Thats exactly where it came from. I've had to fix a lot of bugs with it.
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