[Swift] Converts a UInt64 type integer to [UInt8]

There are two ways to go when you google.

extension UInt64{
    var uint8Array:[UInt8]{
        var x = self.bigEndian
        let data = Data(bytes: &x, count: MemoryLayout<UInt64>.size)
        return data.map{$0}
    var uint8Array2:[UInt8]{
        var bigEndian:UInt64 = self.bigEndian
        let count = MemoryLayout<UInt64>.size
        let bytePtr = withUnsafePointer(to: &bigEndian) {
            $0.withMemoryRebound(to: UInt8.self, capacity: count) {
                UnsafeBufferPointer(start: $0, count: count)
        return Array(bytePtr)

You will get the same result with either. Since it is a good deal, I also compared the speed.

func testPerformanceUInt64ToUInt8() throws{
    let data = (0..<1000000).map{_ in UInt64.random(in: 0..<UInt64.max)}
    self.measure {
        let uint8s = data.map{$0.uint8Array}

func testPerformanceUInt64ToUInt8_2() throws{
    let data = (0..<1000000).map{_ in UInt64.random(in: 0..<UInt64.max)}
    self.measure {
        let uint8s = data.map{$0.uint8Array2}
Test Case '[testPerformanceUInt64ToUInt8]' 
measured [Time, seconds] 
average: 0.176, 
relative standard deviation: 9.656%, 
values: [0.227525, 0.172769, 0.170525, 0.170571, 0.170574, 0.170578, 0.170615, 0.170248, 0.170302, 0.170817]

Test Case '[testPerformanceUInt64ToUInt8_2]' 
measured [Time, seconds] 
average: 0.101, 
relative standard deviation: 8.491%, 
values: [0.126460, 0.098508, 0.098236, 0.097850, 0.097855, 0.097873, 0.097932, 0.097878, 0.097662, 0.097690]

The second one seems to be faster. I find the first way to be easier to understand, but if you need performance, it's better to use the second one.


Recommended Posts

[Swift] Converts a UInt64 type integer to [UInt8]
[Swift] How to send a notification
[Swift5] How to create a splash screen
Convert from C String pointer to Swift String type
[Swift] Type type ~ Enumeration type ~
Convert a string to a character-by-character array with swift
Transition to a view controller with Swift WebKit
[Swift] Type type ~ Structure ~
[Swift5] extension that allows UIImage to be specified by a String type URL
java: How to write a generic type list [Note]
Item 47: Prefer Collection to Stream as a return type
I want to add a reference type column later
I want to create a generic annotation for a type
[Swift] Type components ~ Type nesting ~
[Swift] Type component ~ Subscript ~
[Swift] Type design guidelines
[Swift] Type component ~ Initializer ~
[Swift 5] Draw a line.
[Swift] Shared enumeration type
[Swift] Type type-Class sequel-
[Swift] Type component ~ Method ~
How to type backslash \
Add a local Swift Package to your project with Swift PM
How to write a migration from Rails datetime type to date type
Port C code with a lot of typecasts to Swift
[Java] How to convert a character string from String type to byte type
I tried to convert a string to a LocalDate type in Java
Add a shadow to the Swift Button (and also the circle)