Sensible information to binary operations utilizing the UInt8 kind in Swift

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Representing numbers as integers

Now that we all know what sort of integers can be found in Swift, it is time to speak a bit about what sort of numbers can we symbolize utilizing these information varieties.



print(Int.min)      
print(Int.max)      
print(UInt.min)     
print(UInt.max)     
print(UInt8.min)    
print(UInt8.max)    
print(UInt16.min)   
print(UInt16.max)   
print(UInt32.min)   
print(UInt32.max)   
print(UInt64.min)   
print(UInt64.max)   
print(Int8.min)     
print(Int8.max)     
print(Int16.min)    
print(Int16.max)    
print(Int32.min)    
print(Int32.max)    
print(Int64.min)    
print(Int64.max)    


So there’s a minimal and most worth for every integer kind that we will retailer in a given variable. For instance, we won’t retailer the worth 69420 inside a UInt8 kind, as a result of there are merely not sufficient bits to symbolize this large quantity. 🤓


Let’s look at our 8 bit lengthy unsigned integer kind. 8 bit signifies that now we have actually 8 locations to retailer boolean values (ones and zeros) utilizing the binary quantity illustration. 0101 0110 in binary is 86 utilizing the “common” decimal quantity format. This binary quantity is a base-2 numerical system (a positional notation) with a radix of two. The quantity 86 may be interpreted as:


  • 0*28+1*27+0*26+1*25+0*24 + 1*23+1*22+0*21+0*20
  • 0*128+1*64+0*32+1*16 + 0*8+1*4+1*2+0*1
  • 64+16+4+2
  • 86

We will convert forwards and backwards between decimal and binary numbers, it is not that arduous in any respect, however let’s come again to this matter afterward. In Swift we will examine if a kind is a signed kind and we will additionally get the size of the integer kind by means of the bitWidth property.


print(Int.isSigned)     
print(UInt.isSigned)    
print(Int.bitWidth)     
print(UInt8.bitWidth)   


Primarily based on this logic, now it is fairly simple that an 8 bit lengthy unsigned kind can solely retailer 255 as the utmost worth (1111 1111), since that is 128+64+32+16+8+4+2+1.


What about signed varieties? Properly, the trick is that 1 bit from the 8 is reserved for the optimistic / damaging image. Often the primary bit represents the signal and the remaining 7 bits can retailer the precise numeric values. For instance the Int8 kind can retailer numbers from -128 til 127, for the reason that most optimistic worth is represented as 0111 1111, 64+32+16+8+4+2+1, the place the main zero signifies that we’re speaking a few optimistic quantity and the remaining 7 bits are all ones.


So how the hack can we symbolize -128? Is not -127 (1111 1111) the minimal damaging worth? 😅


Nope, that is not how damaging binary numbers work. With a view to perceive damaging integer illustration utilizing binary numbers, first now we have to introduce a brand new time period known as two’s complement, which is an easy technique of signed quantity illustration.


Primary signed quantity maths


It’s comparatively simple so as to add two binary numbers, you simply add the bits so as with a carry, identical to you’d do addition utilizing decimal numbers. Subtraction then again is a bit tougher, however luckily it may be changed with an addition operation if we retailer damaging numbers in a particular method and that is the place two’s complement is available in.


We could say that we would like so as to add two numbers:


  • 0010 1010 (+42)
  • 0100 0101 +(+69)
  • 0110 1111 =(+111)

Now let’s add a optimistic and a damaging quantity saved utilizing two’s complement, first we have to specific -6 utilizing a signed 8 bit binary quantity format:


  • 0000 0110 (+6)
  • 1111 1001 (one’s complement = inverted bits)
  • 1111 1010 (two’s complenet = add +1 (0000 0001) to at least one’s complement)

Now we will merely carry out an addition operation on the optimistic and damaging numbers.


  • 0010 1010 (+42)
  • 1111 1010 +(-6)
  • (1) 0010 0100 =(+36)

So, you may suppose, what is the cope with the additional 1 to start with of the 8 bit end result? Properly, that is known as a carry bit, and in our case it will not have an effect on our remaining end result, since we have carried out a subtraction as an alternative of an addition. As you possibly can see the remaining 8 bit represents the optimistic quantity 36 and 42-6 is strictly 36, we will merely ignore the additional flag for now. 😅


Binary operators in Swift

Sufficient from the speculation, let’s dive in with some actual world examples utilizing the UInt8 kind. To begin with, we should always speak about bitwise operators in Swift. In my earlier article we have talked about Bool operators (AND, OR, NOT) and the Boolean algebra, now we will say that these capabilities function utilizing a single bit. This time we will see how bitwise operators can carry out numerous transformations utilizing a number of bits. In our pattern instances it is all the time going to be 8 bit. 🤓


Bitwise NOT operator

This operator (~) inverts all bits in a quantity. We will use it to create one’s complement values.



let x: UInt8 = 0b00000110    
let res = ~x                 
print(res)                   
print(String(res, radix: 2)) 


Properly, the issue is that we’ll preserve seeing decimal numbers on a regular basis when utilizing int varieties in Swift. We will print out the proper 1111 1001 end result, utilizing a String worth with the bottom of two, however for some cause the inverted quantity represents 249 in keeping with our debug console. 🙃


It is because the that means of the UInt8 kind has no understanding concerning the signal bit, and the eighth bit is all the time refers back to the 28 worth. Nonetheless, in some instances e.g. whenever you do low stage programming, resembling constructing a NES emulator written in Swift, that is the precise information kind to decide on.

The Information kind from the Basis framework is taken into account to be a set of UInt8 numbers. Truly you will discover various use-cases for the UInt8 kind in the event you take a deeper have a look at the present frameworks & libraries. Cryptography, information transfers, and many others.


Anyway, you can also make an extension to simply print out the binary illustration for any unsigned 8 bit quantity with main zeros if wanted. 0️⃣0️⃣0️⃣0️⃣ 0️⃣1️⃣1️⃣0️⃣



import Basis

fileprivate extension String {
    
    func leftPad(with character: Character, size: UInt) -> String {
        let maxLength = Int(size) - rely
        guard maxLength > 0 else {
            return self
        }
        return String(repeating: String(character), rely: maxLength) + self
    }
}

extension UInt8 {
    var bin: String {
        String(self, radix: 2).leftPad(with: "0", size: 8)
    }
}

let x: UInt8 = 0b00000110   
print(String(x, radix: 2))  
print(x.bin)                
print((~x).bin)             
let res = (~x) + 1          
print(res.bin)


We nonetheless have to offer our customized logic if we need to specific signed numbers utilizing UInt8, however that is solely going to occur after we all know extra concerning the different bitwise operators.


Bitwise AND, OR, XOR operators

These operators works identical to you’d anticipate it from the reality tables. The AND operator returns a one if each the bits have been true, the OR operator returns a 1 if both of the bits have been true and the XOR operator solely returns a real worth if solely one of many bits have been true.


  • AND & – 1 if each bits have been 1
  • OR | – 1 if both of the bits have been 1
  • XOR ^ – 1 if solely one of many bits have been 1

Let me present you a fast instance for every operator in Swift.


let x: UInt8 = 42   
let y: UInt8 = 28   
print((x & y).bin)  
print((x | y).bin)  
print((x ^ y).bin)  


Mathematically talking, there may be not a lot cause to carry out these operations, it will not offer you a sum of the numbers or different fundamental calculation outcomes, however they’ve a special function.

You should use the bitwise AND operator to extract bits from a given quantity. For instance if you wish to retailer 8 (or much less) particular person true or false values utilizing a single UInt8 kind you should use a bitmask to extract & set given elements of the quantity. 😷


var statusFlags: UInt8 = 0b00000100


print(statusFlags & 0b00000100 == 4)   
print(statusFlags & 0b00010000 == 16)  
statusFlags = statusFlags & 0b11101111 | 16
print(statusFlags.bin)  
statusFlags = statusFlags & 0b11111011 | 0
print(statusFlags.bin) 
statusFlags = statusFlags & 0b11101111 | 0
print(statusFlags.bin) 
statusFlags = statusFlags & 0b11101011 | 4
print(statusFlags.bin) 


That is good, particularly in the event you do not need to fiddle with 8 completely different Bool variables, however one there may be one factor that may be very inconvenient about this resolution. We all the time have to make use of the precise energy of two, after all we may use pow, however there’s a extra elegant resolution for this subject.


Bitwise left & proper shift operators

Through the use of a bitwise shift operation you possibly can transfer a bit in a given quantity to left or proper. Left shift is actually a multiplication operation and proper shift is an identical with a division by an element of two.


“Shifting an integer’s bits to the left by one place doubles its worth, whereas shifting it to the precise by one place halves its worth.” – swift.org


It is fairly easy, however let me present you a number of sensible examples so you will perceive it in a bit. 😅


let meaningOfLife: UInt8 = 42



print(meaningOfLife << 1) 
print(meaningOfLife << 2) 
print(meaningOfLife << 3) 
print(meaningOfLife >> 1) 
print(meaningOfLife >> 2) 
print(meaningOfLife >> 3) 
print(meaningOfLife >> 4) 
print(meaningOfLife >> 5) 
print(meaningOfLife >> 6) 
print(meaningOfLife >> 7) 


As you possibly can see now we have to watch out with left shift operations, for the reason that end result can overflow the 8 bit vary. If this occurs, the additional bit will simply go away and the remaining bits are going for use as a remaining end result. Proper shifting is all the time going to finish up as a zero worth. ⚠️


Now again to our standing flag instance, we will use bit shifts, to make it extra easy.


var statusFlags: UInt8 = 0b00000100


print(statusFlags & 1 << 2 == 1 << 2)


statusFlags = statusFlags & ~(1 << 2) | 0
print(statusFlags.bin)


statusFlags = statusFlags & ~(1 << 2) | 1 << 2
print(statusFlags.bin)


As you possibly can see we have used various bitwise operations right here. For the primary examine we use left shift to create our masks, bitwise and to extract the worth utilizing the masks and at last left shift once more to check it with the underlying worth. Contained in the second set operation we use left shift to create a masks then we use the not operator to invert the bits, since we will set the worth utilizing a bitwise or operate. I suppose you possibly can determine the final line based mostly on this data, but when not simply apply these operators, they’re very good to make use of as soon as you recognize all of the little the main points. ☺️


I feel I will reduce it right here, and I am going to make simply one other put up about overflows, carry bits and numerous transformations, possibly we’ll contain hex numbers as nicely, anyway do not need to promise something particular. Bitwise operations are usueful and enjoyable, simply apply & do not be afraid of a little bit of math. 👾

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