PHP Bitwise Operations

A bitwise operation is an operation that works on the individual bits of a number.  Yes, that means the binary(base 2) representation of a number.  These bitwise operations work by exploiting properties of binary numbers to their advantage.  For instance, if the binary representation of a number ends with a 1, it’s odd.

Base 2 Refresher

For those of us who don’t manipulate bits every day (including myself), I thought that a quick refresher on binary representation would be a good idea.  First, let’s create a table.

Trick 1 : Odd / Even

One of the most useful bitwise tricks for web developers is for determining if a number is even or odd.

for($i = 0; $i < 10; $i++) {
     if($i & 1) {
          echo "This is odd.";
     } else {
          echo "This is even.";
     }
}

Trick 2 : Multiplication and Division

//Example 1
$x = 2;
echo $x << 1; //4
echo $x << 2; //8
 
//Example 2
$x = 16;
echo $x >> 1; //8
echo $x >> 2; //4

In example 1, we left shift the number 2 one place.  By left shifting 1 place, it’s the same as multiplying that number by 2.  By left shifting 2 places, it’s the same multiplying the number by 2 twice.

Example 2 is doing bitwise division.  Right shifting by 1 place is the same as dividing the number by 2.  Right shifting by 2 places, is the same is the same as dividing the number by 2 twice.

Others

There are most definitely a ton of other uses for bitwise operators, however these are the ones I use the most.  If you happen to have a favorite, please let everyone know about it in the comments.

For a more in depth introduction to bitwise operations please check out http://en.wikipedia.org/wiki/Bitwise_operation and http://www.litfuel.net/tutorials/bitwise.htm