快速将UInt32拆分为[UInt8] [英] Split UInt32 into [UInt8] in swift

问题描述

我想将 UInt32 添加到我使用 [UInt8] 的字节缓冲区中.在Java中，有一个方便的ByteBuffer类，它具有类似putInt()的方法，用于完全一样的情况.怎么能迅速做到这一点?

I want to add UInt32 to byte buffer for which I use [UInt8]. In java, there is convenient ByteBuffer class that has methods like putInt() for cases exactly like this. How could this be done in swift?

我想我可以解决以下问题:

I guess I could solve this as following:

let example: UInt32 = 72 << 24 | 66 << 16 | 1 << 8 | 15
var byteArray = [UInt8](count: 4, repeatedValue: 0)

for i in 0...3 {
    byteArray[i] = UInt8(0x0000FF & example >> UInt32((3 - i) * 8))
}

这是很冗长，更简单的方法吗?

This is quite verbose though, any simpler way?

推荐答案

您的循环可以更紧凑地写为

Your loop can more compactly be written as

let byteArray = 24.stride(through: 0, by: -8).map {
    UInt8(truncatingBitPattern: example >> UInt32($0))
}

或者，创建一个 UnsafeBufferPointer 并将其转换到数组:

Alternatively, create an UnsafeBufferPointer and convert that to an array:

let example: UInt32 = 72 << 24 | 66 << 16 | 1 << 8 | 15

var bigEndian = example.bigEndian
let bytePtr = withUnsafePointer(&bigEndian) {
    UnsafeBufferPointer<UInt8>(start: UnsafePointer($0), count: sizeofValue(bigEndian))
}
let byteArray = Array(bytePtr)

print(byteArray) // [72, 66, 1, 15]

针对Swift 3(Xcode 8 beta 6)的更新:

var bigEndian = example.bigEndian
let count = MemoryLayout<UInt32>.size
let bytePtr = withUnsafePointer(to: &bigEndian) {
    $0.withMemoryRebound(to: UInt8.self, capacity: count) {
        UnsafeBufferPointer(start: $0, count: count)
    }
}
let byteArray = Array(bytePtr)

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