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    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

    説明

    gmp_popcount(GMP|int|string $num): int

    セットされているビットの数を返します。

    パラメータ

    num

    GMP オブジェクト、整数、あるいは数値に変換可能な数値形式の文字列。

    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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    User Contributed Notes 2 notes

    up
    0
    ketrab2004
    3 years ago
    Another way to get the population count when you don't have the gmp extension is using bitwise operations:

    <?php

    $int     = 133; // 10000101

    for($count = 0; $int != 0; $count++) // repeat until $int is 0 (and count the amount of steps it takes in $count)
    {
    $int = $int & $int-1; // remove the right most 1 from $int using the bitwise and operator
    }

    echo     $count; // 3

    ?>

    This is Kernighan's population count.

    https://youtu.be/ZRNO-ewsNcQ?t=510 has a nice explanation on how it works
    up
    0
    phpmanual at headbank dot co dot uk
    6 years ago
    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.
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