I just did a quick check in C to see if there are any differences.
First result is for loop second Do While. I ran the same test 3 times to
see what differences are. The only difference is the time taken to run the
API to collect the seconds value.
Seconds used = 0.009001
Seconds used = 0.008001
Press ENTER to end terminal session.
Seconds used = 0.008999
Seconds used = 0.007999
Press ENTER to end terminal session.
Seconds used = 0.008001
Seconds used = 0.008001
Press ENTER to end terminal session.
Code
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ledate.h>
int main(int argc, char **argv) {
int i = 0;
int junkl;
int Num_Days = 30;
double start_secs;
double end_secs;
unsigned char junk2[23]; /* Junk char string */
CEELOCT(&junkl, &start_secs,junk2,NULL);
for(i = 0; i < 1000000; i++);
CEELOCT(&junkl, &end_secs,junk2,NULL);
printf("Seconds used = %f\n",end_secs - start_secs);
i = 0;
CEELOCT(&junkl, &start_secs,junk2,NULL);
do {
i++;
}while(i < 1000000);
CEELOCT(&junkl, &end_secs,junk2,NULL);
printf("Seconds used = %f\n",end_secs - start_secs);
exit(0);
}
I know this is not RPG but I thought it would add some additional
information. The for and do loop are doing the same thing because 'i' is
incremented everytime in both instances and the check ofr the value of 'i'
is done on each iteration. Just thought it would be interesting and it
shows the RPG implementation has some differences not found in the C
compiler??
Chris...
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-----Original Message-----
From: rpg400-l-bounces@xxxxxxxxxxxx [mailto:rpg400-l-bounces@xxxxxxxxxxxx]
On Behalf Of Bryce Martin
Sent: June-17-11 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-fast
er-than-using-for-x-number-downto-1
Thanks
Bryce Martin
Programmer/Analyst I
570-546-4777
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