Swift Bitwise Operators (with a couple of practical examples)

5 (4)

Last Updated on March 13, 2022 by Deya Eldeen

Bitwise operators are rarely used in everyday swift programming
⚠️ : not to be confused by Logical Operators like “&&” and “||”

It’s mainly used to perform operations on individual bits,  they are extremely useful and used in Flags, Graphics, Networking, Encryption…

Operator		Description
&		Binary AND
|		Binary OR
^		Binary XOR
~		Binary One’s Complement
<<		Binary Shift Left
>>		Binary Shift Right

First, a refresher on the truth table of XOR, it gives True if both A and B are Different

A	B	Result
TRUE	TRUE	FALSE
TRUE	FALSE	TRUE
FALSE	TRUE	TRUE
FALSE	FALSE	FALSE

The basic code to represent integers as bits, and each operator and it’s result … 🧐

extension Int {
    
    var binaryDescription: String {
        var binaryString = ""
        var internalNumber = self
        for _ in (1...self.bitWidth) {
            binaryString.insert(contentsOf: "\(internalNumber & 1)", at: binaryString.startIndex)
            internalNumber >>= 1
        }
        return "0b " + binaryString
    }
    
}

func bitwise_example() {
    
    let x1 = 0x1
    let x2 = 0x2

    print("x1\t", x1.binaryDescription )
    print("x2\t", x2.binaryDescription )
    
    let binary_and = (x1 & x2)
    let binary_or = (x1 | x2)
    let binary_xor = (x1 ^ x2)
    let binary_complement = (~x1)
    let binary_shiftL = (x1 << 1)
    let binary_shiftR = (x1 >> 1)

    print("&\t",  binary_and.binaryDescription )
    print("|\t", binary_or.binaryDescription )
    
    print("^\t", binary_xor.binaryDescription )
    print("~\t", binary_complement.binaryDescription )
    print("<<\t", binary_shiftL.binaryDescription )
    print(">>\t", binary_shiftR.binaryDescription )
    
}

Output

x1	 0b 0000000000000000000000000000000000000000000000000000000000000001
x2	 0b 0000000000000000000000000000000000000000000000000000000000000010
&	 0b 0000000000000000000000000000000000000000000000000000000000000000
|	 0b 0000000000000000000000000000000000000000000000000000000000000011
^	 0b 0000000000000000000000000000000000000000000000000000000000000011
~	 0b 1111111111111111111111111111111111111111111111111111111111111110
<<	 0b 0000000000000000000000000000000000000000000000000000000000000010
>>	 0b 0000000000000000000000000000000000000000000000000000000000000000

Real Life Usage for them:

1- Color Format Conversion
Most probably, you would have such an extension in your boilerplate iOS app, it converts HEX colors into UIColor.

extension UIColor {
   convenience init(red: Int, green: Int, blue: Int) {
       assert(red >= 0 && red <= 255, "Invalid red component")
       assert(green >= 0 && green <= 255, "Invalid green component")
       assert(blue >= 0 && blue <= 255, "Invalid blue component")

       self.init(red: CGFloat(red) / 255.0, green: CGFloat(green) / 255.0, blue: CGFloat(blue) / 255.0, alpha: 1.0)
   }

   convenience init(rgb: Int) {
       self.init(
           red: (rgb >> 16) & 0xFF,
           green: (rgb >> 8) & 0xFF,
           blue: rgb & 0xFF
       )
   }
}

2- Quick & Dirty hashing

let a = 4012
let b = 8102
let c = 9101

func dirtyHash(a: Int, b: Int, c: Int) -> Int{
    return ( a ^ b ^ c ^ 9999)
}

3- Base64 Encoding

Base64 encoding converts a series of 8 bit bytes into 6 bit character lookup indexes. (SHIFT)ing, (AND)ing, (OR)ing, (NOT)ing are used for implementing the bit operations necessary for Base64 encode/decode.

4- Checking if a number is Odd/Even.

func isEven(number: Int) -> Bool{
    return ((number & 0x1) == 0)
}

func isOdd(number: Int) -> Bool{
    return ((number & 0x1) > 0)
}

5- Solving Problems efficiently and in a performant way.
Write a program to swap the value of two variable.

Using temporary variable

c =  a; a = b; b = c; 

Without using temporary variable

a = a+b; b = a-b; a = a-b; 

Using bitwise operator

a = a^b; b = a^b; a = a^b; 

6- Calculating valid network addresses for a subnet

7- Calculating Permission in Role-based access control systems, RBAC.

8- Calculating Inverse Square Root very fastly
http://h14s.p5r.org/2012/09/0x5f3759df.html

Also:

Some people use bitwise operators to handle multiple error code together, each bit can hold a separate value.

N-bitmap can be a really cool and compact data structure.