如何最快的设置位计数在PHP中的号码吗？ [英] How to fastest count the number of set bits in php?

问题描述

我只是想找到一些速度最快的设置位计数功能在PHP。

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

我看到有好的算法，可以在C ++中实现。 <一href="http://stackoverflow.com/questions/109023/how-to-count-the-number-of-set-bits-in-a-32-bit-integer">How来计算一个32位整数集位数？

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的内置函数或最快的用户自定义功能？

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

推荐答案

您可以尝试敷个面膜用的二进制文件，并用转向考位一个接一个，使用一个循环，将重复32次。

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;
}

您还可以轻松地把你的函数到PHP风格

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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