Just for confirmation:
Linux Mandrake 8.1, PHP 4.0.6, PIII 600MHz, using Jason's code:
- Original code via HTTP:
1st attempt
3.4497429132462
3.1789749860764
[7.85% faster with bit op's]
2nd attempt (reload)
3.3336659669876
3.1573359966278
[5.29% faster with bit op's]
- Original code from the command line:
[bogdan@localhost bogdan]$ php -q ../httpd/mul.php
3.2482839822769
3.1069300174713
[4.35% faster with bit op's]
[bogdan@localhost bogdan]$ php -q ../httpd/mul.php
3.2525320053101
3.1399850845337
[3.46% faster with bit op's]
- Same code, but with $j*4 and $j2:
[bogdan@localhost bogdan]$ php -q ../httpd/mul.php
3.23199903965
[3.0816890001297]
4.65% faster with bit op's
- Same code with $j*256 and $j8:
[bogdan@localhost bogdan]$ php -q ../httpd/mul.php
3.2386699914932
3.0807039737701
[4.88% faster with bit op's]
- Original code (*2 and 1), but also added $q=$p/2; and $q=$p1;
respectively in the two loops:
[bogdan@localhost bogdan]$ php -q ../httpd/mul.php
4.6924660205841
4.4853490591049
[4.41% faster with bit op's]
Switching the loops (making the bit op's loop first and the
multiplication loop second) doesn't change the results.
Bogdan
Jason Wong wrote:
On Monday 20 May 2002 12:03, Martin Towell wrote:
I was doing some timing of a function on the weekend and in one of the
loops, I had to multiply a variable by 2 - easy enough - $i*2
but then I remembered that in C, it's quicker to do a left shift - so $i1
but this actually took longer to execute in php than the $i*2 - can anyone
confirm my test? I iterated ~28,000 times. Each time, there was 2 places
where I was doing the left shift. The time (including all the other stuff I
was doing in the function) for $i*2 was ~12secs, and $i1 was ~19secs.
I am running PHP4.0.6 (download cgi version from php.net) on a win98 system
(500MHz Celeron if that changes anything)
My tests don't show much difference, shifting is slightly faster.
?php
ini_set('max_execution_time', 600);
function gettime() {
list($usec, $sec) = explode( , microtime());
return ((float)$usec + (float)$sec);
}
$start=gettime();
$j = 24;
for($i = 1; $i = 100; $i++) {
$p = $j * 2; #echo $p;
}
$end=gettime();
echo $end - $start, \n;
$start=gettime();
$j = 24;
for($i = 1; $i = 100; $i++) {
$p = $j 1; #echo $p;
}
$end=gettime();
echo $end - $start, \n;
?
Results
===
[jason@x27 jason]$ php -q doo.php
7.4377170801163
7.2966409921646
[jason@x27 jason]$ php -q doo.php
7.4303779602051
7.2926670312881
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