Question

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Understanding PHP's & operator

I was just looking at array_filter() function doc and they had the following code to return odd numbers…

   <?php
    function odd($var)
    {
        // returns whether the input integer is odd
        return($var & 1);
    }
    ?>

Why does $var & 1 return odd number? how does that work?

Answer 1

& is bitwise and. It acts as a mask on the bits of $var. All odd numbers end with 1

no  bit  &1
1   001  1
2   010  0
3   011  1
4   100  0
5   101  1
6   110  0
7   111  1