gmp_popcount

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

gmp_popcount — Population count

说明

gmp_popcount ( GMP $a ) : int

Get the population count.

参数

a: 可以是一个 GMP 数据 resouce，或一个可以转换为数值的字符串。

返回值

The population count of a, as an integer.

范例

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";
?>

以上例程会输出：

3
7

User Contributed Notes

phpmanual at headbank dot co dot uk 18-Nov-2018 03:51


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.