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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
12 days 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
3 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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