Perl - 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.

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:

$x = 50;
$y = 25;

#Bitwise OR and assignment operation
$x |= $y;

#Displaying the result
print("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.

sub MaxPowerOfTwo {
  #passing argument
  $n = $_[0];  

  #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 = $n + 1;

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

print("MaxPowerOfTwo(100) = ".MaxPowerOfTwo(100)."\n");
print("MaxPowerOfTwo(500) = ".MaxPowerOfTwo(500)."\n");
print("MaxPowerOfTwo(1000) = ".MaxPowerOfTwo(1000)."\n");      

The above code will give the following output:

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