callback function return return($var & 1)?

Question

I have read the PHP Manuel about array_filter

Answer 1

An odd number has its zeroth (least significant) bit set to 1:

           v
0 = 00000000b
1 = 00000001b
2 = 00000010b
3 = 00000011b
           ^

The expression $var & 1 performs a bitwise AND operation between $var and 1 (1 = 00000001b). So the expression will return:

• 1 when $var has its zeroth bit set to 1 (odd number)
• 0 when $var has its zeroth bit set to 0 (even number)