note 104031 deleted from language.operators.bitwise by danbrown
| From: | danbrown@php.net | Date: | Wed, 18 May 2011 14:43:43 +0000 |
| Subject: | note 104031 deleted from language.operators.bitwise by danbrown | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-179852@lists.php.net to get a copy of this message | ||
Note Submitter: phil
----
A general comment in response to Josh: reconsider using pow() when a simple power of 2 is needed,
especially in cases where this operation must be done many times. Bit-shift operations are much
faster than resorting to chained multiplication or floating-point operations, which is what I assume
the pow() function does. To benchmark the differences, run this program:
<?php
$tick = microtime(true);
for ($i = 0; $i < 1000000; ++$i) {
for ($j = 0; $j < 64; ++$j) {
$k = pow(2, $j);
}
}
$tock = microtime(true);
print "Time using pow: " . ($tock - $tick) . " seconds\n";
$tick = microtime(true);
for ($i = 0; $i < 1000000; ++$i) {
for ($j = 0; $j < 64; ++$j) {
$k = (1 << $j);
}
}
$tock = microtime(true);
print "Time using <<: " . ($tock - $tick) . " seconds\n";
?>
On my system, I find that the bit-shift operator is about 4 times faster than pow() when calculating
powers of 2.