gmp_popcount()

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

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

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

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.