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Optimize array_slice for packed/unpacked arrays with large offsets #4860

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Optimize array_slice for packed/unpacked arrays with large offsets #4860

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TysonAndre
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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;

nikic
nikic reviewed Oct 25, 2019
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@TysonAndre
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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 TysonAndre force-pushed the array_slice-optimization branch from 8af7046 to 602d104 Compare October 25, 2019 23:04
@TysonAndre TysonAndre changed the title Optimize array_slice for packed arrays with large offsets Optimize array_slice for packed/unpacked arrays with large offsets Oct 25, 2019
@TysonAndre
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The review comments have been addressed. The build failure was due to a mac OS job encountering a networking issue.

nikic
nikic reviewed Oct 26, 2019
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nikic
nikic reviewed Oct 26, 2019
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nikic
nikic reviewed Oct 26, 2019
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@TysonAndre
Optimize array_slice for packed arrays with large offsets
c6c0eb8 
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.
@TysonAndre TysonAndre force-pushed the array_slice-optimization branch from afa3dfb to c6c0eb8 Compare October 26, 2019 14:20
nikic
nikic reviewed Oct 26, 2019
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@php-pulls php-pulls closed this in e7ff590 Oct 28, 2019
TysonAndre added a commit to TysonAndre/php-src that referenced this pull request Oct 29, 2019
@TysonAndre
Update documentation/comment for phpGH-4860
7b9a94c 
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.
php-pulls pushed a commit that referenced this pull request Oct 30, 2019
@TysonAndre @nikic
Update documentation/comment for GH-4860
96f361d 
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]
@carusogabriel carusogabriel added this to the PHP 8.0 milestone May 29, 2020
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