# PHP - Bitwise OR and assignment operator

The Bitwise OR and assignment operator (|=) assigns the first operand a value equal to the result of Bitwise OR operation of two operands.

(x |= y) is equivalent to (x = x | y)

The Bitwise OR operator (|) is a binary operator which takes two bit patterns of equal length and performs the logical OR operation on each pair of corresponding bits. It returns 1 if either or both bits at the same position are 1, else returns 0.

Bit_1Bit_2Bit_1 | Bit_2
000
101
011
111

The example below describes how bitwise OR operator works:

```50 | 25 returns 59

50    ->    110010  (In Binary)
| 25    ->  | 011001  (In Binary)
----        --------
59    <-    111011  (In Binary)
```

The code of using Bitwise OR operator (|) is given below:

```<?php
\$x = 50;
\$y = 25;

//Bitwise OR and assignment operation
\$x |= \$y;

//Displaying the result
echo "x = \$x";
?>
```

The output of the above code will be:

```x = 59
```

### Example: Find largest power of 2 less than or equal to given number

Consider an integer 1000. In the bit-wise format, it can be written as 1111101000. However, all bits are not written here. A complete representation will be 32 bit representation as given below:

```00000000000000000000001111101000
```

Performing N |= (N>>i) operation, where i = 1, 2, 4, 8, 16 will change all right side bit to 1. When applied on 1000, the result in 32 bit representation is given below:

```00000000000000000000001111111111
```

Adding one to this result and then right shifting the result by one place will give largest power of 2 less than or equal to 1000.

```00000000000000000000001000000000
```

The below code will calculate the largest power of 2 less than or equal to given number.

```<?php
function MaxPowerOfTwo(\$N) {
//changing all right side bits to 1.
\$N |= (\$N>>1);
\$N |= (\$N>>2);
\$N |= (\$N>>4);
\$N |= (\$N>>8);
\$N |= (\$N>>16);

//adding 1 to \$N makes smallest power
//of 2 greater than given number
\$N += 1;

//right shift by one position makes
//largest power of 2 less than or
//equal to given number
\$N >>= 1;
return \$N;
}

echo "MaxPowerOfTwo(100) = ".
MaxPowerOfTwo(100)."\n";
echo "MaxPowerOfTwo(500) = ".
MaxPowerOfTwo(500)."\n";
echo "MaxPowerOfTwo(1000) = ".
MaxPowerOfTwo(1000)."\n";
?>
```

The above code will give the following output:

```MaxPowerOfTwo(100) = 64
MaxPowerOfTwo(500) = 256
MaxPowerOfTwo(1000) = 512
```

❮ PHP - Operators

5