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https://github.com/uraimo/Bitter

A Swift Bits Manipulation/Bitwise Operations Toolkit
https://github.com/uraimo/Bitter

bit-manipulation bitset bitwise-operators

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A Swift Bits Manipulation/Bitwise Operations Toolkit

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README 

        


	Bitter

	


	


		Swift 4 compatible

		License: MIT

		

		

		

		Travis CI

	





## Summary



The Bitter library extends all the basic Swift Int types with some useful methods for manipulating bits.

The objective of the library is to make the code dealing with bits and bitwise operations more concise and readable, through the use of shorthand methods where they make sense.

With Bitter you'll be able for example, to replace this:



```swift

var i:UInt32 = 0xAABBCCDD

let tmp = (i & (0xFF << 16)) >> 16 // Let's swap the 2nd and 3rd byte...

i = (i & ~(0xFF << 16)) | ((i & (0xFF << 8)) << 8)

i = (i & ~(0xFF << 8)) | (tmp << 8)

i = (i & ~((0x1 << 3) << 8)) | (i & ((0x1 << 3) << 8)) // Set the 4th bit of the 2nd byte

```

With this:

```swift

let tmp = i[2] // Let's swap the 2nd and 3rd byte!

i[2] = i[1]

i[1] = tmp 

i[1] = i[1].setb3(1) // Set the 4th bit of the 2nd byte

i[1] = i[1].setb3(0).setb4(1).setb5(0).setb6(1) // Let's set some other bit

```



## Installation



If you want to install Bitter manually just include all the Swift files in `Sources/Bitter` in your project or load it as a git submodule.



Bitter also supports all the major dependency managers: CocoaPods, Carthage and SwiftPM.



To use Bitter in your project with [CocoaPods](https://www.cocoapods.org/), add it to your `PodFile`:



```

use_frameworks!



pod 'Bitter'

```



And update your workspace with `pod install`. 



Bitter is also available through Carthage. To install just write into your Cartfile:



```

github "uraimo/Bitter"

```



Download the framework with `carthage update` and add it to your embedded binaries.



And if you are using the Swift Package Manager just add it to the dependencies of your `Package.swift`:



```

// swift-tools-version:4.0

import PackageDescription



let package = Package(

    ...

    dependencies: [

        .package(url: "https://github.com/uraimo/Bitter.git", from: "4.0.0")

    ]

)

```

Regardless of how you added Bitter to your project, import it with `import Bitter`.



## Usage



Let's see what Bitter provides:



#### Int type conversion



Every time you want to convert an Int containing a bit pattern to a smaller Int you need to perform a *truncating* bit conversion because the conversion will simply **fail at runtime** if the content of your integer is bigger than what the receiving type allows (e.g. try `Int8(1000)`). And let me reiterate that we are performing a bit truncation, not a decimal truncating conversion.



Bit pattern truncating conversions can be easily performed using the constructor `init(truncatingIfNeeded:)`, but if you need to do this a lot, your code will become unreadable fast.



With Bitter, every Int*n*/UInt*n* type gains a few methods that allows to perform truncating bit pattern conversions to smaller Int types or simple bit pattern conversion for bigger and same size/different signedness Int types: **.to8, toU8, to16, toU16, to32, toU32, to64, toU64**.

The toU*n* methods perform a conversion to unsigned Int while the number refers to the size of the type, e.g.  `.toU16` will convert the current integer to an UInt16 truncating the bit pattern if necessary.



Let's see an example:

```swift

var i:Int32 = 50000

var u8:UInt8 = i.toU8   //81, Without Bitter: var u8:UInt8 = UInt8(truncatingIfNeeded:i)

```



Bitter is also useful in mixed types expression, making the code more concise:

```swift

class Test{

    var content:UInt32=0



    func shiftAndResizeMe(howMuch:Int)->UInt16{

        return  (content << howMuch.toU32).toU16  //Without Bitter: return UInt16(truncatingIfNeeded:(content << UInt32(truncatingIfNeeded:howMuch)))

    }

}

```



#### Specific Byte subscript



While retrieving and modifying a single byte in a multi-byte Int is easy, having to write always the same code is a bit annoying and Bitter adds subscript to address single bytes to every Int type. Following the same safety-first approach of the Int conversions, trying to modify a byte outside of the range of the current type will result in an error at runtime.



Let's see some examples:

```swift

var i:UInt32 = 0xAABBCCDD



//Let's swap the two bytes

let tmp = i[2]           //Without Bitter: let tmp = (i & (0xFF << 16)) >> 16

i[2] = i[1]              //                i = (i & ~(0xFF << 16)) | ((i & (0xFF << 8)) << 8)

i[1] = tmp               //                i = (i & ~(0xFF << 8)) | (tmp << 8)



// Let's set to 0 the second bit of the second byte

i[1] &= 0b11111101       //Without Bitter: i = i & (0b11111101 << 8)



// Let's change the fourth byte

i[4] = 0xAA   //Error! There is no 4th byte!

``` 

The subscript index start from the LSB to the MSB for little endian multi-byte Ints and in the opposite direction if a big endian conversion has been applied to the Int.



#### Modifying specific bits



Every Int type, signed or not, gains 8 properties and 8 functions that allow to set or get a single bit in the first byte of the integer. They are supposed to be used in tandem with the byte subscript:



```swift

var i:UInt32 = 0xAABBCCDD

i[2].b2 //0

i[2].b3 //1



i[2] = i[2].setb2(1).setb3(0)

i[2].b2 //1

i[2].b3 //0

```

The `.bN` property returns the value of the bit at the specific position, while the `.setbN(value)` function sets a specific bit in a integer (the indexes refer to the 8 less significant bits) and return the modified 8 bits integer (if used on integers with content larger than 8 bits, the rest is truncated).



Considering that every `.setbN(value)` function returns a new integer, these functions can be concatenated to modify more than one bit. This function can be used in conjunction with byte indexed subscripts as shown above where on the right side we build a new byte value for the position 2 of the array that will be then assigned to the same position of the same array.



#### Other functionalities



Bitter also adds a few other extensions to Int types:



* Double negation operator `~~`: This new operator has the same function that **!!** has in C or similar languages, it converts every integer value not equal to 0 to 1 and keeps the value 0 the same. Extremely useful when you want to convert the result of an expression to the standard C 0/1 integer boolean to use it in another expression.



* `size` static property for Int types: Shorthand for `MemoryLayout.stride`  



* `mask(bits:msb:)` static method: It creates a bitmask with the requested number of bits set, starting from the most significant bit or not. For example, calling `Int16.mask(5,msb:true)` will return `0xF800` or `1111100000000000` in binary, while `Int16.mask(5,msb:false)` will return `0x001F`, since the five bits will be set starting from the less significant position. 



#### Bitwise operations



To learn more about bitwise operations in Swift, see the article "[Dealing with Bit Sets in Swift](https://www.uraimo.com/2016/02/05/Dealing-With-Bit-Sets-In-Swift/)" on my blog (updated to Swift 4.0).



## Contributing



First of all, thanks for considering contributing to this project, all PRs are welcome!



Please notice that the sources for this library are not written directly in Swift but are generated using [Sourcery](https://github.com/krzysztofzablocki/Sourcery).



 The main Bitter template is located at `Templates/Bitter.stencil` and the `compile.sh` script will take care of downloading Sourcery and compiling the stencil template to Swift sources.



Releases older than 3.x use the [GYB](https://www.uraimo.com/2016/02/09/a-short-swift-gyb-tutorial/) template compiler.