拆分成UInt32的[UINT8]斯威夫特

Question

我想UInt32添加到了，我用[UInt8]字节的缓冲区。在Java中，有就是有一个像putInt（）的方法对完全一样的情况下方便的ByteBuffer类。这怎么可能在迅速完成？

我想我可以解决这个问题如下：

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))
}

这是相当冗长不过，任何简单的方法？

Answer 1

您的回路可以更紧凑地写为

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

另外，创建一个UnsafeBufferPointer和将其转换成一个数组：

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]

更新夫特3（Xcode的8个β6）：

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)

Answer 2

@马丁改进的r回答。他的工作是UINT16，UInt32的，和UINT64：

protocol UIntToBytesConvertable {
    var toBytes: [Byte] { get }
}

extension UIntToBytesConvertable {
    func toByteArr<T: Integer>(endian: T, count: Int) -> [Byte] {
        var _endian = endian
        let bytePtr = withUnsafePointer(to: &_endian) {
            $0.withMemoryRebound(to: Byte.self, capacity: count) {
                UnsafeBufferPointer(start: $0, count: count)
            }
        }
        return [Byte](bytePtr)
    }
}

extension UInt16: UIntToBytesConvertable {
    var toBytes: [Byte] {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt16>.size)
    }
}

extension UInt32: UIntToBytesConvertable {
    var toBytes: [Byte] {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt32>.size)
    }
}

extension UInt64: UIntToBytesConvertable {
    var toBytes: [Byte] {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt64>.size)
    }
}

Answer 3

您可以从施放一个UnsafeMutablePointer类型到另：

var arr = UnsafeMutablePointer<UInt32>.alloc(1)
arr.memory = example
var arr2 = UnsafeMutablePointer<UInt8>(arr)

Answer 4

我有一个类似的问题在Xcode 8 Beta中6：写这行

var value = String(cString: sqlite3_column_text(stmt, index))

   to


let txt = UnsafePointer<Int8>(sqlite3_column_text(stmt, index))

问题和解决问题

Answer 5

@马丁改进的r回答。

func toByteArrary<T>(value: T)  -> [UInt8] where T: UnsignedInteger, T: FixedWidthInteger{
  var bigEndian = value.bigEndian
  let count = MemoryLayout<T>.size
  let bytePtr = withUnsafePointer(to: &bigEndian) {
    $0.withMemoryRebound(to: UInt8.self, capacity: count) {
        UnsafeBufferPointer(start: $0, count: count)
    }
  }

  return Array(bytePtr)
}

Answer 6

另一种选择是，直接扩展FixedWidthInteger协议，所以任何UnsignedInteger自动获得功能是免费的。这是它的外观基础上@本森的回答：

extension FixedWidthInteger where Self: UnsignedInteger {

    var bytes: [UInt8] {
        var _endian = littleEndian
        let bytePtr = withUnsafePointer(to: &_endian) {
            $0.withMemoryRebound(to: UInt8.self, capacity: MemoryLayout<Self>.size) {
                UnsafeBufferPointer(start: $0, count: MemoryLayout<Self>.size)
            }
        }
        return [UInt8](bytePtr)
    }

}

我们可以用一个单元测试验证这一点：

func test_bytes() {
    XCTAssertEqual(UInt8.min.bytes, [0])
    XCTAssertEqual(UInt8.max.bytes, [255])

    XCTAssertEqual(UInt16.min.bytes, [0, 0])
    XCTAssertEqual(UInt16.max.bytes, [255, 255])

    XCTAssertEqual(UInt32.min.bytes, [0, 0, 0, 0])
    XCTAssertEqual(UInt32.max.bytes, [255, 255, 255, 255])

    XCTAssertEqual(UInt64.min.bytes, [0, 0, 0, 0, 0, 0, 0, 0])
    XCTAssertEqual(UInt64.max.bytes, [255, 255, 255, 255, 255, 255, 255, 255])
}