Just had the two loops laying around that I was messing with and decided
to time them. I also have done a test on (for x=1 to bigNum) and it was
actually slower than the for/downto test. Not a ton slower, but some.
Incrementing/Decrementing... either way... the relative performance
difference is still there.
Thanks
Bryce Martin
Programmer/Analyst I
570-546-4777
"Morgan, Paul" <Paul.Morgan@xxxxxxxxxxx>
Sent by: rpg400-l-bounces@xxxxxxxxxxxx
06/17/2011 09:47 AM
Please respond to
RPG programming on the IBM i / System i <rpg400-l@xxxxxxxxxxxx>
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RPG programming on the IBM i / System i <rpg400-l@xxxxxxxxxxxx>
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Subject
RE: Performance test: DOW vs FOR.... interesting results...
Martin,
Why are you decrementing the For loop but incrementing the Do While?
Paul Morgan
Principal Programmer Analyst
IT Supply Chain/Replenishment
-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of Bryce Martin
Sent: Friday, June 17, 2011 9:37 AM
To: RPG programming on the IBM i / System i
Subject: Performance test: DOW vs FOR.... interesting results...
Ok, so out of curiosity yesterday I was doing some DOW vs FOR comparisons
and thought that while I was at it I would do a performance test...and
this uncovered something interesting...
Here's the long of the short of it...
DOW is 3x faster than FOR. If you use OPTIMIZE(*FULL) then the gap is
even greater.
Now, before anyone says it... yes...we're talking about milliseconds here.
But think of all your programs that have loops...yep, almost all of them.
So I guess my main question is this...
Why the big relative difference? How is it that FOR can be so much worse
than DOW? You can actually see a difference if doing 10's or 100's of
millions of iterations. So while most people won't see a difference in
individual instances, if all your FOR loops were 3 times faster in all
your programs, I can't help but think you might be able to see some actual
performance across a fairly taxed system.
I don't know... just ruminating. Anybody have any gritty details?
See this link for code and discussion....
http://www.code400.com/forum/showthread.php/10499-DOW-x-lt-y-is-3-times-faster-than-using-for-x-number-downto-1
Thanks
Bryce Martin
Programmer/Analyst I
570-546-4777
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