JavaScript - Bitwise OR operator

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:

var x = 50;
var y = 25;
var z, txt;

//Bitwise OR operation
z = x | y;
txt = "z = " + z;

The output (value of txt) after running above script will be:

z = 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 | (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.

function MaxPowerOfTwo(N) {
  //changing all right side bits to 1.
  N = N | (N>>1);
  N = N | (N>>2);
  N = N | (N>>4);
  N = N | (N>>8);
  N = 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;
}

var txt;
txt = "MaxPowerOfTwo(100) = " + 
        MaxPowerOfTwo(100) + "<br>";
txt = txt + "MaxPowerOfTwo(500) = " + 
        MaxPowerOfTwo(500) + "<br>";
txt = txt + "MaxPowerOfTwo(1000) = " + 
        MaxPowerOfTwo(1000)+ "<br>";

The output (value of txt) after running above script will be:

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