If you don't have gmp extension enabled (or don't want to use it for any reason), you can get popcount of an int using decbin() and substr_count().
<?php
$int1 = 133;
$bin1 = decbin($int1); // "10000101"
echo substr_count($bin1, "1");
// Result: 3
?>
Being a string-comparison this is far less efficient than gmp_popcount() (for which there is a dedicated instruction on most if not all modern processors), but may be handy if gmp is unavailable, or in non-performance-critical code that doesn't otherwise need it.
gmp_popcount
(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)
gmp_popcount — セットされているビットの数
戻り値
num にセットされているビットの数を返します。
例
例1 gmp_popcount() の例
<?php
$pop1 = gmp_init("10000101", 2); // 1 が 3 つ
echo gmp_popcount($pop1) . "\n";
$pop2 = gmp_init("11111110", 2); // 1 が 7 つ
echo gmp_popcount($pop2) . "\n";
?>上の例の出力は以下となります。
3 7
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phpmanual at headbank dot co dot uk ¶
5 years ago
