algorithm - How to fastest count the number of set bits in php?

Question

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

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

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?

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

Answer 1

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;
}

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;
}