JavaScript - 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:

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

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

The output (value of txt) after running above script 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.

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;
}

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

❮ JavaScript - Operators

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