(PHP 4 >= 4.0.4, PHP 5, PHP 7)
gmp_popcount — Population count
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The population count of a, as an integer.
Example #1 gmp_popcount() example
<?php
$pop1 = gmp_init("10000101", 2); // 3 1's
echo gmp_popcount($pop1) . "\n";
$pop2 = gmp_init("11111110", 2); // 7 1's
echo gmp_popcount($pop2) . "\n";
?>
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3 7