Re: Performance: While or For loop

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