callback function return return($var & 1)?

Question

I have read the PHP Manuel about array_filter

Answer 1

It is performing a bitwise AND with $var and 1. Since 1 only has the last bit set, $var & 1 will only be true if the last bit is set in $var. And since even numbers never have the last bit set, if the AND is true the number must be odd.

Answer 2

$var & 1 - is bitwise AND it checks if $var is ODD value

0 & 0 = 0,
0 & 1 = 0,
1 & 0 = 0,
1 & 1 = 1 

so, first callback function returns TRUE only if $var is ODD, and second - vise versa (! - is logical NOT).

Answer 3

You know && is AND, but what you probably don't know is & is a bit-wise AND.

The & operator works at a bit level, it is bit-wise. You need to think in terms of the binary representations of the operands.

e.g.

710 & 210 = 1112 & 0102 = 0102 = 210

For instance, the expression $var & 1 is used to test if the least significant bit is 1 or 0, odd or even respectively.

$var & 1

010 & 110 = 0002 & 0012 = 0002 = 010 = false (even)

110 & 110 = 0012 & 0012 = 0012 = 110 = true  (odd)

210 & 110 = 0102 & 0012 = 0002 = 010 = false (even)

310 & 110 = 0112 & 0012 = 0012 = 110 = true  (odd)

410 & 210 = 1002 & 0012 = 0002 = 010 = false (even)

and so on...

Answer 4

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)

Answer 5

& is a bitwise AND on $var.

If $var is a decimal 4, it's a binary 100. 100 & 1 is 100, because the right most digit is a 0 in $var - and 0 & 1 is 0, thus, 4 is even.

Answer 6

& 

it's the bitwise operator. It does the AND with the corrispondent bit of $var and 1

Basically it test the last bit of $var to see if the number is even or odd

Example with $var binary being 000110 and 1

000110 &
     1
------
     0

0 (false) in this case is returned so the number is even, and your function returns false accordingly