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gmp_popcount

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

gmp_popcountPopulation 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

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User Contributed Notes 1 note

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phpmanual at headbank dot co dot uk
1 year 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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