Optimize array_slice for packed/unpacked arrays with large offsets by TysonAndre · Pull Request #4860 · php/php-src

TysonAndre · 2019-10-25T13:37:09Z

If the offset is 100000, and there are no gaps in the packed array,
then advance the pointer once by 100000(1+99999),
instead of looping and skipping 100000 times.

This was validated with this test script. Unit tests continue to pass locally:

<?php
$example = range('x', 1000000);
$start = microtime(true);
$output = '';
for ($i = 0; $i < 10; $i++) {
    $value = array_slice($example, 999900 + $i, 5);
    $output .= json_encode($value) . "\n";
}
// With this patch:    0.000010 (best run)
// Without this patch: 0.026424
printf("Elapsed time: %.6f\n", microtime(true) - $start);
echo $output;

TysonAndre · 2019-10-25T14:08:56Z

Also, I should probably make the same optimization for $preserve_keys=true - It'd be inconsistent to have one be thousands of times slower than the other.

TysonAndre · 2019-10-26T00:12:49Z

The review comments have been addressed. The build failure was due to a mac OS job encountering a networking issue.

If the offset is 100000, and there are no gaps in the packed/unpacked array, then advance the pointer once by 100000, instead of looping and skipping 100000 times. Add a new test of array_slice handling unset offsets.

Fix folding for the new helper method. Clarify comment in UPGRADING: The performance on associative arrays would also improve, as long as no offsets were unset (no gaps). Packed arrays can have gaps.

Fix folding for the new helper method. Clarify comment in UPGRADING: The performance on associative arrays would also improve, as long as no offsets were unset (no gaps). Packed arrays can have gaps. Closes GH-4873. [ci skip]

nikic reviewed Oct 25, 2019

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