循环sizeof（$ x）与循环（$ x）的实际速度/基准？

Question

I'm confused about the speed of the sizeof($x) vs $x when in a loop. This site: phpbench.com claims that the loop of sizeof($x) without pre calc -count() is THOUSANDS of percent slower than with pre calc count(). So I did a test as below, but I'm not sure if this is the right way to test it. The results show that the time is almost the same for each function. So I don't understand how it would be so much different from the phpbench website.

In summary, I'd like to know a definite answer if function a (with sizeof($unset)) is really considerably slower than function b (with pre calculated $unset value). I think now the values/functions are stored in memory so sizeof($x) could actually be faster than on servers from several years ago?

<?php

$v=0;

function a()
{
//sizeof
$unset=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o');

for($i=0;$i<sizeof($unset);$i++) {$v=$v+1;}

return;
}

function b()
{
//pre calculated
$unset=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o');

for($i=0;$i<15;$i++) {$v=$v+1;}

return;
}

function benchmark($func)
{

    $start = microtime(true);
    for ($i = 0; $i < 500000; $i++) {
        $func();
    }
    $end = microtime(true);
    $time = $end - $start;

    echo $func . " time: " . sprintf('%.4f', $time) . PHP_EOL.'<br>';
}

benchmark('a'); // sizeof
benchmark('b'); // count

?>

Answer 1

According to my benchmarking sizeof() and count() perform about the same, however to squeeze more performance out of the loop itself you can do the following:

for($i=0, $c=sizeof($unset);$i<$c;$i++){
  $v=$v+1;
}

This should give it a performance boost because it doesn't have to evaluate with a function in each loop cycle.

The system I've used is here with the following code:

$b = new \Benchmark(10000);

$b->register('sizeof', function(){
  $unset=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o');
  for($i=0;$i<sizeof($unset);$i++) {$v=$v+1;}
});

$b->register('count', function(){
  $unset=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o');
  for($i=0;$i<count($unset);$i++) {$v=$v+1;}
});

$b->register('count 2', function(){
  $unset=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o');
  for($i=0, $c=count($unset);$i<$c;$i++) {$v=$v+1;}
});

$b->register('preset', function(){
  $unset=array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o');
  for($i=0;$i<15;$i++) {$v=$v+1;}
});

print_r($b->start());

With this as the results:

Array
(
    [stats] => Array
        (
            [phpversion] => 7.1.1
            [itterations] => 40000
            [duration] => 0.1180682182
            [fastest] => preset
            [slowest] => sizeof
        )

    [results] => Array
        (
            [0] => Array
                (
                    [name] => preset
                    [time] => 0.0265829563
                    [average] => 0.0000026583
                    [speed] => 19.73%
                )

            [1] => Array
                (
                    [name] => count 2
                    [time] => 0.0271441936
                    [average] => 0.0000027144
                    [speed] => 18.04%
                )

            [2] => Array
                (
                    [name] => count
                    [time] => 0.0312242508
                    [average] => 0.0000031224
                    [speed] => 5.71%
                )

            [3] => Array
                (
                    [name] => sizeof
                    [time] => 0.0331168175
                    [average] => 0.0000033117
                    [speed] => 0.00%
                )

        )

)