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POPHP why is continue n slower than using break
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copied!<p>Please consider the following code:</p> <pre><code>$start = microtime(); for($i = 2; $i < 100; $i++) { for($y = 2; $y <= sqrt($i); $y++) { if($i%$y != 0) { continue; } else { continue 2; } } echo $i.','; } echo "\nFinished in " . (microtime() - $start); </code></pre> <p>Given that the above code effectively uses continue 2 to break the inner loop and skip any code post the inner loop, why does the following code on average execute faster when it appears to do more:</p> <pre><code> $start = microtime(); for($i = 2; $i < 100; $i++) { $flag = true; for($y = 2; $y <= sqrt($i); $y++) { if($i%$y != 0) { continue; } else { $flag = false; break; } } if($flag === true) echo $i.','; } echo "\nFinished in " . (microtime() - $start); </code></pre> <p>Thanks for any input.</p> <p><em><strong></em>__<em>_</em>__<em></strong> Update <strong></em>__<em>_</em>__<em>_</em>__<em>_</em>__<em>_</em></strong></p> <p>Thanks for the feedback but we seem to have missed the point. Regardless of if this is good programming practice I was trying to understand why the performance difference (which is tiny but consistent) is not within the bias I expected.</p> <p>The passing of true to microtime seems insignificant as both samples are measured using the same method with the same overhead and the same inaccuracy.</p> <p>More than one run was tested, as implied by use of the word average.</p> <p>Just for illustration please consider the following small samples using microtime(true) which shows the same pattern as using microtime().</p> <p>I know this is a small sample but the pattern is quite clear:</p> <p>Continue 0.00037288665771484 0.00048208236694336 0.00046110153198242 0.00039386749267578 0.0003662109375</p> <p>Break 0.00033903121948242 0.00035715103149414 0.00033307075500488 0.00034403800964355 0.00032901763916016</p> <p>Thanks for looking, and thanks for any further feedback.</p> <p><em><strong></em>__<em>_</em>___<em></strong> UPDATE Further investigation <strong></em>__<em>_</em>__<em>_</em>__<em>_</em>___</strong></p> <p>Interestingly if the echo statements are removed from the code the continue performs faster, with the echo statements in place break is faster.</p> <p>Please consider the following code sample, and consider that the results are in conflict dependant on if the echo statements are removed or not:</p> <pre><code><?php $breakStats = array(); $continueStats = array(); ob_start(); for($i = 0; $i < 10000; $i++) { $breakStats[] = doBreakTest(); $continueStats[] = doContinueTest(); } ob_clean(); echo "<br/>Continue Mean " . (array_sum($continueStats) / count($continueStats)); echo "<br/>Break Mean " . (array_sum($breakStats) / count($breakStats)); function doBreakTest() { $start = microtime(true); for($i = 2; $i < 100; $i++) { $flag = true; $root = sqrt($i); for($y = 2; $y <= $root; $y++) { if($i%$y != 0) { continue; } else { $flag = false; break; } } } if($flag === true) echo $i . ''; return microtime(true) - $start; } function doContinueTest() { $start = microtime(true); for($i = 2; $i < 100; $i++) { $root = sqrt($i); for($y = 2; $y <= $root; $y++) { if($i%$y != 0) { continue; } else { echo $i . ''; continue 2; } } } return microtime(true) - $start; } </code></pre> <p>Echo statements present :</p> <p>Continue Mean 0.00014134283065796 Break Mean 0.00012669243812561</p> <p>Echo statements not present :</p> <p>Continue Mean 0.00011746988296509 Break Mean 0.00013022310733795</p> <p>Note that by removing the echo statement from the break and flag test we also remove the ($flag === true) check, so the load should reduce, but continue in this case still wins. W</p> <p>So in a pure continue n versus break + flag scenario, it appears that continue n is the faster contstruct. But add an equal number of identical echo statements, and the continue n performance flags.</p> <p>This makes sense to me logically that continue n should be faster, but I would have expected to see the same with the echo statements present.</p> <p>This is clearly a difference in the generated opcodes, and the position of the echo statement (inner loop vs outer loop) does anyone know a way of seeing the opcodes generated? This I suppose is ultimatley what I need as I am trying to understand what is happening internally.</p> <p>Thanks :)</p>

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