Performance: While or For loop

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Date: Sat, 24 Mar 2007 10:21:07 -0400
To: php-general@lists.php.net
Content-Type: text/plain; charset="us-ascii" ; format="flowed"
Subject: Re: [php] Performance: While or For loop
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At 7:47 PM -0500 3/23/07, Richard Lynch wrote:
>Folks:
>
>How often do you use a loop of any kind in PHP with enough iterations
>that this is even significant?
>
>Write the code that makes sense.
>
>Optimize the biggest bottleneck until performance is acceptable.

Absolutely -- the time we take discussing these types of concerns
probably cost more cycles than the sum total of all the "optimized"
savings in the lifetime of all the computers on earth.

The time you spend trying to make something faster in those terms
clearly cost more time in development and maintenance. It's a
trade-off that's not worth it.

Q: Do they teach this stuff in college now or are the teachers still
only measuring performance in myopic terms of saving memory and time?
Not a criticism, just a question.

Cheers,

tedd

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Hi,

Does somebody has benchmarks of what is faster, while or for loop?

Thanks,

Tijnema

does this help?

http://www.php.lt/benchmark/phpbench.php

Jake



> -----Original Message-----
> From: Tijnema ! [mailto:tijnema@gmail.com]
> Sent: Thursday, March 22, 2007 4:38 PM
> To: PHP
> Subject: [php] Performance: While or For loop
>
> Hi,
>
> Does somebody has benchmarks of what is faster, while or for loop?
>
> Thanks,
>
> Tijnema
>
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> PHP General Mailing List (http://www.php.net/)
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>
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> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.17/730 - Release
> Date: 3/22/2007 7:44 AM
>
>

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7:44 AM

On 3/22/07, Jake McHenry <linux@nittanytravel.com> wrote:
> does this help?
>
> http://www.php.lt/benchmark/phpbench.php
>
> Jake

Well, there wasn't a test between For and While, so i did it myself,
and i'm quite confused about the result.
I let PHP count from 0 to 100000000 on my 1ghz AMD Athlon.
While did it in a average time of 55 seconds.
For did it in a average time of 59 seconds.
It's not a big difference, if you see what number it needs to go to,
but there is a difference.

code used:
<?php
set_time_limit(100000);
echo date("H:i:s");
for($i = 0; $i < 100000000;$i++)
{
}
echo date("H:i:s");
$x = 0;
while($x < 100000000)
{
$x++;
}
echo date("H:i:s");
?>

So, use while loops instead of for loops ;)

Tijnema

ps. I also did the while loop before the for loop, doesn't matter.

>
>
>
> > -----Original Message-----
> > From: Tijnema ! [mailto:tijnema@gmail.com]
> > Sent: Thursday, March 22, 2007 4:38 PM
> > To: PHP
> > Subject: [php] Performance: While or For loop
> >
> > Hi,
> >
> > Does somebody has benchmarks of what is faster, while or for loop?
> >
> > Thanks,
> >
> > Tijnema
> >
> > --
> > PHP General Mailing List (http://www.php.net/)
> > To unsubscribe, visit: http://www.php.net/unsub.php
> >
> > --
> > No virus found in this incoming message.
> > Checked by AVG Free Edition.
> > Version: 7.5.446 / Virus Database: 268.18.17/730 - Release
> > Date: 3/22/2007 7:44 AM
> >
> >
>
> --
> No virus found in this outgoing message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.17/730 - Release Date: 3/22/2007
> 7:44 AM
>
>
> --
> PHP General Mailing List (http://www.php.net/)
> To unsubscribe, visit: http://www.php.net/unsub.php
>
>

On 3/22/07, Jon Anderson <janderson@gamingsolutions.ca> wrote:
> Your test isn't exactly fair. The for loop has no statements in it, and
> the while loop has one. Your tests show while as approx 7% faster, while
> a modified test shows an approximate 30% speed improvement:
>
> Do this:
>
> for ($i=0;$i<10000000;$i++) {}
>
> v.s.:
>
> $i = 0;
> while ($i++ < 10000000) {}
>
> The above while loop is 30% faster than the for. A little teaking on the
> for loop, it's faster still:

I was comparing the way people normal use while and for. But this does
confirms what i said, while is faster.
>
> for ($i=10000000;$i--;) {}
>
> A little tweaking on the while, and it's faster yet:
>
> $i = 10000000;
> while ($i--) {}
>
> The last while loop is around 60% faster on my hardware than the first
> for loop.
>
> jon
>
> Tijnema ! wrote:
> > On 3/22/07, Jake McHenry <linux@nittanytravel.com> wrote:
> >> does this help?
> >>
> >> http://www.php.lt/benchmark/phpbench.php
> >>
> >> Jake
> >
> > Well, there wasn't a test between For and While, so i did it myself,
> > and i'm quite confused about the result.
> > I let PHP count from 0 to 100000000 on my 1ghz AMD Athlon.
> > While did it in a average time of 55 seconds.
> > For did it in a average time of 59 seconds.
> > It's not a big difference, if you see what number it needs to go to,
> > but there is a difference.
> >
> > code used:
> > <?php
> > set_time_limit(100000);
> > echo date("H:i:s");
> > for($i = 0; $i < 100000000;$i++)
> > {
> > }
> > echo date("H:i:s");
> > $x = 0;
> > while($x < 100000000)
> > {
> > $x++;
> > }
> > echo date("H:i:s");
> > ?>
> >
> > So, use while loops instead of for loops ;)
> >
> > Tijnema
> >
> > ps. I also did the while loop before the for loop, doesn't matter.
> >
> >>
> >>
> >>
> >> > -----Original Message-----
> >> > From: Tijnema ! [mailto:tijnema@gmail.com]
> >> > Sent: Thursday, March 22, 2007 4:38 PM
> >> > To: PHP
> >> > Subject: [php] Performance: While or For loop
> >> >
> >> > Hi,
> >> >
> >> > Does somebody has benchmarks of what is faster, while or for loop?
> >> >
> >> > Thanks,
> >> >
> >> > Tijnema
> >> >
> >> > --
> >> > PHP General Mailing List (http://www.php.net/)
> >> > To unsubscribe, visit: http://www.php.net/unsub.php
> >> >
> >> > --
> >> > No virus found in this incoming message.
> >> > Checked by AVG Free Edition.
> >> > Version: 7.5.446 / Virus Database: 268.18.17/730 - Release
> >> > Date: 3/22/2007 7:44 AM
> >> >
> >> >
> >>
> >> --
> >> No virus found in this outgoing message.
> >> Checked by AVG Free Edition.
> >> Version: 7.5.446 / Virus Database: 268.18.17/730 - Release Date:
> >> 3/22/2007
> >> 7:44 AM
> >>
> >>
> >> --
> >> PHP General Mailing List (http://www.php.net/)
> >> To unsubscribe, visit: http://www.php.net/unsub.php
> >>
> >>
> >
>
>

Tijnema ! wrote:

> On 3/22/07, Jon Anderson <janderson@gamingsolutions.ca> wrote:
>
>> Your test isn't exactly fair. The for loop has no statements in it, and
>> the while loop has one. Your tests show while as approx 7% faster, while
>> a modified test shows an approximate 30% speed improvement:
>>
>> Do this:
>>
>> for ($i=0;$i<10000000;$i++) {}
>>
>> v.s.:
>>
>> $i = 0;
>> while ($i++ < 10000000) {}
>

This has been asked many times, probably likewise for every language.
Search for the same question on the C programming language for a more in
depth discussion of this and to find out why one way is faster than the
other...

Major factor: Don't forget the difference between pre and post increment
operators. $i++ and ++$i.

For reference this is my PHP test script and results:

{{{
tdoherty@gamma tdoherty $ cat ./forwhile.php
<?
$i=0; $start = microtime(TRUE);
for ($i=0; $i<100000; ++$i) {}
echo sprintf("For pre-increment ($i): %0.3f\n",microtime(TRUE) - $start);

$i=0; $start = microtime(TRUE);
for ($i=0; $i<100000; $i++) {}
echo sprintf("For post-increment ($i): %0.3f\n",microtime(TRUE) - $start);

$i=0; $start = microtime(TRUE);
while (++$i < 100000) {}
echo sprintf("While pre-increment ($i): %0.3f\n",microtime(TRUE) - $start);

$i=0; $start = microtime(TRUE);
while ($i++ < 100000) {}
echo sprintf("While post-increment ($i): %0.3f\n",microtime(TRUE) - $start);
?>
tdoherty@gamma tdoherty $ php ./forwhile.php
For pre-increment (100000): 0.035
For post-increment (100000): 0.060
While pre-increment (100000): 0.029
While post-increment (100001): 0.056
}}}

After multiple runs I see that the for pre-increment loop is fastest.
Note that the while loop with a post-increment runs once more than with
a pre-increment.

Everytime I run, the results are *very* different, though still fall
within similar comparitive domains.

Travis Doherty

On Fri, Mar 23, 2007 at 12:24:45AM -0500, Travis Doherty wrote:
> After multiple runs I see that the for pre-increment loop is fastest.
> Note that the while loop with a post-increment runs once more than with
> a pre-increment.
>
> Everytime I run, the results are *very* different, though still fall
> within similar comparitive domains.

Hi...

I used your script and my results are different from yours.
The post-while increment is generally the fastest result on my
machine (Core 2 Duo, php 5.2.1 and apache 2.2.4).

I ran the script multiple times:

[schnipp ]

For pre-increment (100000): 0.066
For post-increment (100000): 0.066
While pre-increment (100000): 0.028
While post-increment (100001): 0.025

[schnipp ]

Greetings
Mario

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On 3/23/07, Mario Guenterberg <mg@havelsoft.com> wrote:
> On Fri, Mar 23, 2007 at 12:24:45AM -0500, Travis Doherty wrote:
> > After multiple runs I see that the for pre-increment loop is fastest.
> > Note that the while loop with a post-increment runs once more than with
> > a pre-increment.
> >
> > Everytime I run, the results are *very* different, though still fall
> > within similar comparitive domains.
>
> Hi...
>
> I used your script and my results are different from yours.
> The post-while increment is generally the fastest result on my
> machine (Core 2 Duo, php 5.2.1 and apache 2.2.4).
>
> I ran the script multiple times:
>
> [schnipp ]
>
> For pre-increment (100000): 0.066
> For post-increment (100000): 0.066
> While pre-increment (100000): 0.028
> While post-increment (100001): 0.025
>
> [schnipp ]
>
> Greetings
> Mario

Well, myh results are a little bit confusing again, if using
pre-increment, for shows up faster now. But while post-increment is
the fastest :) Is there any logic why we all have different results?
does it has to do something with the type of CPU, i'm using AMD
Athlon. 1800+ (clocked down from 133 to 100 * 11.5)

For pre-increment (100000): 0.026
For post-increment (100000): 0.030
While pre-increment (100000): 0.029
While post-increment (100001): 0.023

Tijnema

ps. @ Mario: Youre C2D got owned by a AMD 1.15Ghz :)


>
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> -----------------------------------------------------
> | havelsoft.com - Ihr Service Partner für Open Source |
> | Tel: 033876-21 966 |
> | Notruf: 0173-277 33 60 |
> | http://www.havelsoft.com |
> | |
> | Inhaber: Mario Günterberg |
> | Mützlitzer Strasse 19 |
> | 14715 Märkisch Luch |
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>
>

On Thu, March 22, 2007 5:14 pm, Tijnema ! wrote:
> On 3/22/07, Jon Anderson <janderson@gamingsolutions.ca> wrote:
>> Your test isn't exactly fair. The for loop has no statements in it,
>> and
>> the while loop has one. Your tests show while as approx 7% faster,
>> while
>> a modified test shows an approximate 30% speed improvement:
>>
>> Do this:
>>
>> for ($i=0;$i<10000000;$i++) {}
>>
>> v.s.:
>>
>> $i = 0;
>> while ($i++ < 10000000) {}
>>
>> The above while loop is 30% faster than the for. A little teaking on
>> the
>> for loop, it's faster still:

Folks:

How often do you use a loop of any kind in PHP with enough iterations
that this is even significant?

Write the code that makes sense.

Optimize the biggest bottleneck until performance is acceptable.

--
Some people have a "gift" link here.
Know what I want?
I want you to buy a CD from some indie artist.
http://cdbaby.com/browse/from/lynch
Yeah, I get a buck. So?

On 3/24/07, Richard Lynch <ceo@l-i-e.com> wrote:
> On Thu, March 22, 2007 5:14 pm, Tijnema ! wrote:
> > On 3/22/07, Jon Anderson <janderson@gamingsolutions.ca> wrote:
> >> Your test isn't exactly fair. The for loop has no statements in it,
> >> and
> >> the while loop has one. Your tests show while as approx 7% faster,
> >> while
> >> a modified test shows an approximate 30% speed improvement:
> >>
> >> Do this:
> >>
> >> for ($i=0;$i<10000000;$i++) {}
> >>
> >> v.s.:
> >>
> >> $i = 0;
> >> while ($i++ < 10000000) {}
> >>
> >> The above while loop is 30% faster than the for. A little teaking on
> >> the
> >> for loop, it's faster still:
>
> Folks:
>
> How often do you use a loop of any kind in PHP with enough iterations
> that this is even significant?
>
> Write the code that makes sense.
>
> Optimize the biggest bottleneck until performance is acceptable.

It was more likely to get an idea if there was a real difference or
not, and apparently there is not really a big difference.

But well if you are going to create a script where 1000+ loops are,
you might get a few seconds faster script :)

Tijnema
>
> --
> Some people have a "gift" link here.
> Know what I want?
> I want you to buy a CD from some indie artist.
> http://cdbaby.com/browse/from/lynch
> Yeah, I get a buck. So?
>
>