Swift Bitwise and Bit Shift Operators

# Swift Bitwise and Bit Shift Operators

#### In this tutorial, you'll learn about different bitwise operations in Swift. These are used for bit level computation in an expression.

A bit is used to denote a binary digit. A binary digit can have two possible values either 0 or 1. As a beginner level programmer, you don't have to work with operations at the bit level.

Working with primitive data types such as: integer, float, boolean, string etc is enough. You may need to work at bit level when you are dealing with low level programming.

Swift provides a rich set of operators, apart from basic operators, to manipulate bits. These operators are similar to the logical operators, except that they work on binary representations of data (bits).

Bitwise operators are operators that are used to change individual bits of an operand. Operand is a variable or constant in which the operation is done.

All bitwise operators available in swift are listed below:

## 1. Bitwise NOT Operator

It is represented by tilde `~` sign and can be applied on a single operand. This inverts all the bits. i.e changes 1 to 0 and 0 to 1.

If x is a variable/constant that holds binary value i.e 0 or 1. The bitwise not operation on the x variable can be represented in table below:

NOT
x ~x
0 1
1 0

### Example 1: Bitwise NOT operator for unsigned integer

``````let initalNumber:UInt8 = 1
let invertedNumber = ~initalNumber
print(invertedNumber)
``````

When you run the above program, the output will be:

`254`

In the above program, the statement `let initalNumber:UInt8 = 1` is of type Unsigned int of size 8 bits. So, 1 in decimal can be represented as `00000001` in binary.

The bitwise not operator changes all the bit of a variable or constant, the bit 0 is changed to 1 and 1 to 0. So invertedNumber contains bits `11111110`. After converting it into decimal it is represented as 254. So, the statement `print(invertedNumber)` outputs 254 in the screen.

You can also perform bitwise operator directly in the bits as:

### Example 2: Bitwise NOT operator in bits

``````let initialBits: UInt8 = 0b11111111
let invertedBits = ~initialBits
print(invertedBits)
``````

When you run the above program, the output will be:

`0`

initialBits contains binary value `11111111` that corresponds to 255 in decimal. To represent the number in binary we have `0b` as a prefix in the literal. Without `0b` as a prefix, it will treat it as a normal integer and you will get an overflow error (UInt8 can store numbers from only 0 to 255).

Since, we have used bitwise not operator, it changes all the 1 to 0. So, the constant invertedBits contains `00000000` which is equivalent to 0 in `UInt8`.

### Example 3: Bitwise NOT operator for signed integer

``````let initalNumber:Int = 1
let invertedNumber = ~initalNumber
print(invertedNumber)
``````

When you run the above program, the output will be:

`-2`

In the above program, 1 in decimal can be represented as `00000001` in binary. The bitwise not operator changes all the bit of a variable or constant, the bit 0 is changed to 1 and 1 to 0. So, invertedNumber contains bits `11111110`. This should output 254 in the screen. But instead returns -2. Strange, Right?? Let's explore below how did this happen.

`let initalNumber:Int = 1` is a signed int that can hold both positive and negative integers. That's why when we applied not operator for a signed integer, the returned binary may also represent a negative number.

How did compiler interpreted -2 as `11111110 ` in binary?

The compiler used Two's complement to represent integers. To get the two's complement negative notation of an integer, you should first write out the number in binary then invert the digits, and add one to the result.

Steps to find out Two's complement of -2:

1. Write 2 in binary form: `00000010`
2. Invert the digits. 0 becomes 1 and 1 becomes 0 : `11111101`
3. Add 1 : `11111110`

That's how compiler interprets binary number `1111110` as `-2` in decimal. But, there is a little twist that compiler made which we did not notice. It also inferred the type of invertedNumber as `Int8` type.

To understand this, let's see an example below:

``````print(Int8(bitPattern: 0b11111110))
print(0b11111110)``````

When you run the above program, the output will be:

```-2
254```

In the above example, compiler treated the binary number to -2 in decimal only for the Signed 8-Bit Integer. Therefore statement `print(Int8(bitPattern: 0b11111110))` outputs -2 in the screen.

But for the normal integer type whose size is 32/64 bit and can hold large values, it interprets the value as `254`. Therefore, statement `print(0b11111110)` outputs 254 in the screen.

## 2. Bitwise AND Operator

It is represented by `&` and can be applied on two operands. The AND operator compares two bits and returns 1 if both bits are 1, otherwise returns 0.

If x and y are variable/constant that holds binary value i.e 0 or 1. The Bitwise AND operation on x and y can be represented in table below:

AND
x y x & y
0 0 0
0 1 0
1 1 1
1 0 0

### Example 5: Bitwise AND operation

``````let xBits = 0b10000011
let yBits = 0b11111111
let result = xBits & yBits
print(result)``````

When you run the above program, the output will be:

```Binary: 10000011
131
```

In the above program, the statement `let result = xBits & yBits` combines the bits of two operands xBits and yBits. It returns 1 it both of the bits are 1 otherwise it returns 0.

`String(value , radix: )` initializer is used to represent number in different number system. If we supply radix value 2. It converts the number to binary number system. Similarly, we can use 16 for hex and 10 for decimal.

The statement `print("Binary:",String(result, radix: 2))` outputs Binary: 10000011 in the screen. `10000011` is equivalent to 131 in decimal,the statement `print(result)` outputs 131 in the console.

## 3. Bitwise OR Operator

It is represented as `|` and can be applied on two operands. The bitwise OR operator compares two bits and generates a result of 1 if one or more of its inputs are 1 otherwise 0.

If x and y are variable/constant that holds binary value i.e 0 or 1. The Bitwise OR operation on x and y can be represented in table below:

OR
x y x | y
0 0 0
0 1 1
1 1 1
1 0 1

### Example 6 : Bitwise OR operation

``````let xBits = 0b10000011
let yBits = 0b11111111
let result = xBits | yBits
print(result)
``````

When you run the above program, the output will be:

```Binary: 11111111
255
```

In the above program, the statement `let result = xBits | yBits` combines the bits of two constants xBits and yBits. It returns 1 if any of the bits are 1 otherwise it returns 0.

The statement `print("Binary:",String(result, radix: 2))` outputs Binary: 11111111 in the screen. Since, `11111111`is equivalent to `255` in decimal, the statement `print(result)` outputs 255 in the screen.

## 4. Bitwise XOR operator

It is represented as `^` and can be applied on two operands. The XOR operator compares two bits and generates a result of 1 if exactly one of its inputs are 1 otherwise it returns 0.

If x and y are variable/constant that holds binary value i.e 0 or 1. The Bitwise XOR operation on x and y can be represented in table below:

XOR
x y x ^ y
0 0 0
0 1 1
1 1 0
1 0 1

### Example 7 : Bitwise XOR operation

``````let xBits = 0b10000011
let yBits = 0b11111111
let result = xBits ^ yBits
print(result)
``````

When you run the above program, the output will be:

```Binary: 1111100
124
```

In the above program, the statement `let result = xBits ^ yBits` combines the bits of two constants xBits and yBits. It returns 1 if exactly one of the bits is 1 otherwise it returns 0.

The statement `print("Binary:",String(result, radix: 2))` outputs Binary: 1111100 (equivalent to 01111100)in the screen. Since, `1111100` is equivalent to `124` in decimal, the statement `print(result)` outputs 124 in the screen.

## 5. Bitwise Shift Operator

This operators are used to move all bits in a number to the left or the right by a certain number of places and can be applied on single operand. It is represented as `<<` or `>>`.

There are two kinds of shift operators:

### Bitwise left shift operator

• Denoted as `<<`
• It causes the bits to be shifted to the left specified by the number followed by `<<`.
• The bit positions that have been vacated by the shift operation are zero-filled.
• Shifting an integer's bits to the left by one position doubles its value

#### Example 8: Bitwise left shift operator

``````let someBits:UInt8 = 0b11000100
print(someBits << 1)
``````

When you run the above program, the output will be:

`136`

In the above program, we have used left shift operator. Using `<<` 1 means to shift the bit by 1 to the left. The digits get shifted to the left by one position, and the last digit on the right is filled with a zero.

You can also see the digit that gets shifted "off the end" from left side is lost. It does not wrap around again from the right. Shifting it one bit to the left removes the 1 from the binary and adds 0 in the right to fill the shifted value as well rest of the other bits are shifted towards left position by 1.

This returns `10001000` which is equivalent to `136` in `UInt8`. Therefore, `print(someBits << 1)`statement outputs 136 in the screen.

### Bitwise right shift operator

• Denoted as `>>`
• It causes the bits to be shifted to the right by the number followed by `>>`
• For unsigned numbers, the bit positions that have been vacated by the shift operation are zero-filled.
• For signed numbers (numbers that can also be negative), the sign bit is used to fill the vacated bit positions. In other words, if the number is positive, 0 is used, and if the number is negative, 1 is used.
• Shifting it to the right by one position halves its value.

#### Example 9: Bitwise right shift operator for unsigned integer

``````let someBits: UInt8 = 4
print(someBits >> 1)
``````

When you run the above program, the output will be:

`2`

In the above program, we have used right shift operator on a unsigned integer. Using `>>` 1 means to shift the the bit by 1 to the right. The bit positions that have been vacated by the shift operation are always zero-filled on a unsigned integer.

Since, 4 is represented as `00000100` in binary. Shifting it one bit to the right, returns `00000010` which is equivalent to `2` in `UInt8`. Therefore, `print(someBits >> 1)` statement outputs 2 in the screen.

#### Example 10: Bitwise right shift operator for signed integer

``````let someBits:Int = -4
print(someBits >> 1)
``````

When you run the above program, the output will be:

`-2`

In the above program, we have used right shift operator on a unsigned integer. Unlike positive numbers, using `>>` for negative numbers, 1 is used to fill the vacant place, instead of 0.

Since, `-4` is represented as `11111100` in binary. Shifting it one bit to the right and placing 1 in vacant position, returns `11111110` which is equivalent to `-2` for `Int8` type. Therefore, `print(someBits >> 1)`statement outputs -2 in the screen.