Just a data point here.
I tried compiling the sources you posted. However, you didn't
provide the value of CONST_BITS you were using. It looks like your
snippets are from jidctint.c, so I used the value from that file
(13). In both of your examples, I got the direct muls version, not
the __lmul__ version.
However, neither did I get the constant #-1730 to show up in my
disassembly, so perhaps my value of CONST_BITS is incorrect. The
difference might also be because of the simpler (extracted) code I
was using, compared to your using the entire function.
-- Keith Rollin
-- Palm OS Emulator engineer
At 11:04 PM +0100 1/10/03, Jan Slodicka wrote:
It is from JPEG official library.
<SNIP>
----- Original Message -----
From: "Ben Combee" <[EMAIL PROTECTED]>
To: "Palm Developer Forum" <[EMAIL PROTECTED]>
Sent: Friday, January 10, 2003 10:49 PM
Subject: Re: CW compiler
At 22:19 2003-1-10 +0100, you wrote:
>I just observed very strange thing.
>
>By changing the source line order the same source line (multiplication)
is
>translated either into
>
> movea.w d4,a0
> move.l a0,86(a7)
> move.l a0,d0
> move.l #-1730,d1
> jsr __lmul__
> move.l d0,d3
>
>or into
>
> move.w d6,d3
> muls.w #-1730,d3
>
>The second alternative seems to be optically shorter, but it actually
uses
>register value inherited from the previous code. That's OK.
>What I don't understand is that in one case the multiplication is
realized
>via muls instruction, in the other a call to the emulator is used
instead.
Could you show the lines of code? The first one is doing a signed 32-bit
multiplication, while the second is doing a signed 16-bit
multiplication. Is it possible that with one line order, you've got a
long
temporary result that's affecting the multiplication?
--
Ben Combee <[EMAIL PROTECTED]>
CodeWarrior for Palm OS technical lead
Palm OS programming help @ www.palmoswerks.com
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