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Swift - left shift operator assignment



The Bitwise left shift assignment operator (<<=) assigns the first operand a value equal to the result of Bitwise left shift operation of two operands.

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

The Bitwise left shift operator (<<) takes the two numbers and left shift the bits of first operand by number of place specified by second operand. For example: for left shifting the bits of x by y places, the expression (x<<y) can be used. It is equivalent to multiplying x by 2y.

The example below describes how left shift operator works:

1000 << 2 returns 4000

                      (In Binary)
   1000         ->    1111101000  
   << 2                     |  left shift the bits
   -----                    V  by 2 places
   4000         <-  111110100000 
                      (In Binary) 

The code of using left shift operator (<<) is given below:

var x = 1000

//left shift assignment operation
x <<= 2

//Displaying the result
print("x = \(x)")

The output of the above code will be:

x = 4000

Example: Count number of 1 Bits in a positive integer

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  

Bitwise AND operation with 1 at any bit results into 1 if the bit is 1 or 0 if the bit is 0. Performing such operation at every bit, and counting the number of 1 gives the count of 1 bits in the given positive integer. To achieve this bitwise left shift assignment operator can be used as shown in the example below:

func CountOneBits(_ n:Int) -> Int { 
  var mask = 1
  var count = 0
  
  //performing bitwise AND operation
  //at every bit of the number
  for _ in 0...31 {
    if((mask & n) == mask) { 
      count += 1
    }
    mask <<= 1
  }
  return count
}

print("CountOneBits(1000) = \(CountOneBits(1000))")
print("CountOneBits(1023) = \(CountOneBits(1023))")

The above code will give the following output:

CountOneBits(1000) = 6
CountOneBits(1023) = 10

❮ Swift - Operators

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