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gmp_popcount

(PHP 4 >= 4.0.4, PHP 5, PHP 7, PHP 8)

gmp_popcountComptage de population

Description

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

Dénombre la population de num.

Liste de paramètres

num

Un objet GMP, un entier, ou une chaîne de caractères numérique.

Valeurs de retour

La population de num, sous la forme d'un int.

Exemples

Exemple #1 Exemple avec gmp_popcount()

<?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";
?>

L'exemple ci-dessus va afficher :

3
7

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User Contributed Notes 2 notes

up
0
ketrab2004
2 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
5 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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