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Bug #70754 array_udiff compares the same values multiple times
Submitted: 2015-10-21 01:40 UTC Modified: -
Avg. Score:5.0 ± 0.0
Reproduced:0 of 1 (0.0%)
From: php_bugs at multiwebinc dot com Assigned:
Status: Open Package: Performance problem
PHP Version: 7.0.0RC5 OS:
Private report: No CVE-ID: None
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 [2015-10-21 01:40 UTC] php_bugs at multiwebinc dot com
All versions of PHP seem to be inefficient at executing array_udiff. The values in $a in the callback function are all compared twice. If the callback function is expensive, this would affect performance.

Also, some comparisons are unnecessary.

Test script:
/* Note: The callback function just returns 0 every time, which means that all values in both arrays are considered equal. */

function callback($a, $b) {
    echo "\$a = $a; \$b= $b; ";
    echo "<br>\n";
    return 0;

$array1 = array("first_0", "first_1", "first_2", "first_3", "first_4" );
$array2 = array("second_0", "second_1", "second_2", "second_3", "second_4");
$result = array_udiff($array1, $array2, "callback");

Actual result:
$a = first_2; $b= first_1;
$a = first_4; $b= first_2;
$a = first_2; $b= first_0;
$a = first_3; $b= first_2;
$a = first_4; $b= first_3; // Unnecessary since we already know these are equal
$a = first_1; $b= first_0; // Unnecessary since we already know these are equal
$a = second_2; $b= second_1;
$a = second_4; $b= second_2;
$a = second_2; $b= second_0;
$a = second_3; $b= second_2;
$a = second_4; $b= second_3; // Unnecessary since we already know these are equal
$a = second_1; $b= second_0; // Unnecessary since we already know these are equal
$a = first_4; $b= second_4;
$a = first_4; $b= first_3; // Duplicate. Already tested above.
$a = first_3; $b= first_2; // Duplicate. Already tested above.
$a = first_2; $b= first_1; // Duplicate. Already tested above.
$a = first_1; $b= first_0; // Duplicate. Already tested above.


CPVsri (last revision 2015-10-21 09:48 UTC by mandersonaugusto at bol dot com dot br)

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