如何最快地计算 php 中设置的位数?

How to fastest count the number of set bits in php?(如何最快地计算 php 中设置的位数?)

问题描述

我只是想在php中找到一些最快的设置位计数功能.

I just want to find some fastest set bits count function in the php.

例如，0010101 => 3、00011110 => 4

For example, 0010101 => 3, 00011110 => 4

我看到有很好的算法可以用 c++ 实现.如何计算数量在 32 位整数中设置位?

I saw there is good Algorithm that can be implemented in c++. How to count the number of set bits in a 32-bit integer?

有没有php内置函数或者最快的用户自定义函数?

Is there any php built-in function or fastest user-defined function?

推荐答案

您可以尝试使用二进制 AND 应用掩码，并使用 shift 逐位测试，使用将迭代 32 次的循环.

You can try to apply a mask with a binary AND, and use shift to test bit one by one, using a loop that will iterate 32 times.

function getBitCount($value) {

    $count = 0;
    while($value)
    {
        $count += ($value & 1);
        $value = $value >> 1;
    }

    return $count;
}

您还可以轻松地将您的函数放入 PHP 样式中

You can also easily put your function into PHP style

function NumberOfSetBits($v)
{
    $c = $v - (($v >> 1) & 0x55555555);
    $c = (($c >> 2) & 0x33333333) + ($c & 0x33333333);
    $c = (($c >> 4) + $c) & 0x0F0F0F0F;
    $c = (($c >> 8) + $c) & 0x00FF00FF;
    $c = (($c >> 16) + $c) & 0x0000FFFF;
    return $c;
}

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