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> -----Original Message-----
> From: Jason Wong
> Sent: 27/12/04 10:16
>
> On Monday 27 December 2004 12:40, Richard Lynch wrote:
>
> > If you want to mimic the behaviour of abs (allowing for positive
> numbers)
> > and performance was an issue, that:
> > $x = ($x < 0) ? - $x : $x;
> >
> > is most likely faster than abs()
>
> Having nothing better to do I decided to benchmark this:
>
> ternary:
>
> $doo = -20;
> for ($i = 1; $i < 10000000; $i++) {
> $dah = ($doo < 0) ? - $doo : $doo;
> }
>
> abs():
>
> $doo = -20;
> for ($i = 1; $i < 10000000; $i++) {
> $dah = abs($doo);
> }
That's not a valid benchmark, since only on the first pass through the loop
is $doo negative. Personally, I'd want to test it with equal numbers of
positive and negative values, and I'd want to know the contribution of the
loop and value-setup overhead, so I'd write it like this:
$t = microtime();
$oh = $t[1] + $t[0];
for ($i=1; $i<10000000; $i++) {
$doo = 20 * ($i%2?-1:1);
}
$t = microtime();
$oh = $t[1] + $t[0] -$oh;
$t = microtime();
$tern = $t[1] + $t[0];
for ($i=1; $i<10000000; $i++) {
$doo = 20 * ($i%2?-1:1);
$dah = ($doo<0) ? -$doo : $doo;
}
$t = microtime();
$tern = $t[1] + $t[0] -$tern;
$t = microtime();
$abs = $t[1] + $t[0];
for ($i=1; $i<10000000; $i++) {
$doo = 20 * ($i%2?-1:1);
$dah = abs($doo);
}
$t = microtime();
$tern = $t[1] + $t[0] - $abs;
echo "<p>Overhead = ", number_format($oh, 2), "sec<br />\n";
echo "Ternary = ", number_format($tern, 2),
" sec; less overhead = ", number_format($tern-$oh, 2),
" sec<br />\n";
echo "Abs() = ", number_format($abs, 2),
" sec; less overhead = ", number_format($abs-$oh, 2),
" sec\n</p>";
I don't have access to a php system right now, or I'd run it (just out of
curiosity!). Anyone who wants to grab the above and test it is welcome...
;)
Cheers!
Mike
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