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Comment convertir un double en tableau d'octets dans swift?

Je sais comment le faire en Java (voir ici ), mais je n’ai pas trouvé d’équivalent Swift pour ByteBuffer, et par conséquent sa méthode .putDouble (valeur double) .

func doubleToByteArray(value: Double) -> [UInt8]? {
    . . .
}
doubleToByteArray(1729.1729) // should return [64, 155, 4, 177, 12, 178, 149, 234]
iosswiftbytebytearraybytebuffer
15
Panini Raman
typealias Byte = UInt8

func toByteArray<T>(var value: T) -> [Byte] {
    return withUnsafePointer(&value) {
        Array(UnsafeBufferPointer(start: UnsafePointer<Byte>($0), count: sizeof(T)))
    }
}

toByteArray(1729.1729)
toByteArray(1729.1729 as Float)
toByteArray(1729)
toByteArray(-1729)

Mais les résultats sont inversés par rapport à vos attentes (à cause de l’endianité):

[234, 149, 178, 12, 177, 4, 155, 64]
[136, 37, 216, 68]
[193, 6, 0, 0, 0, 0, 0, 0]
[63, 249, 255, 255, 255, 255, 255, 255]

Ajoutée:

func fromByteArray<T>(value: [Byte], _: T.Type) -> T {
    return value.withUnsafeBufferPointer {
        return UnsafePointer<T>($0.baseAddress).memory
    }
}

let a: Double = 1729.1729
let b = toByteArray(a) // -> [234, 149, 178, 12, 177, 4, 155, 64]
let c = fromByteArray(b, Double.self) // -> 1729.1729

Pour Xcode8/Swift3.0:

func toByteArray<T>(_ value: T) -> [UInt8] {
    var value = value
    return withUnsafePointer(to: &value) {
        $0.withMemoryRebound(to: UInt8.self, capacity: MemoryLayout<T>.size) {
            Array(UnsafeBufferPointer(start: $0, count: MemoryLayout<T>.size))
        }
    }
}

func fromByteArray<T>(_ value: [UInt8], _: T.Type) -> T {
    return value.withUnsafeBufferPointer {
        $0.baseAddress!.withMemoryRebound(to: T.self, capacity: 1) {
            $0.pointee
        }
    }
}

Pour Xcode8.1/Swift3.0.1

func toByteArray<T>(_ value: T) -> [UInt8] {
    var value = value
    return withUnsafeBytes(of: &value) { Array($0) }
}

func fromByteArray<T>(_ value: [UInt8], _: T.Type) -> T {
    return value.withUnsafeBytes {
        $0.baseAddress!.load(as: T.self)
    }
}
46
rintaro

Eh bien, ce n’était pas facile, mais le voici:

func doubleToByteArray(value: Double) -> [UInt8] {
    let count = sizeof(Double)
    var doubles: [Double] = [value]
    let data = NSData(bytes: doubles, length: count)
    var result = [UInt8](count: count, repeatedValue: 0)
    data.getBytes(&result, length: count)
    return result
}

Utiliser avec précaution.

6
vacawama

Solution dans Swift 3:

public func toByteArray<T>(_ value: T) -> [Byte] {
  let totalBytes = MemoryLayout<T>.size
  var value = value
  return withUnsafePointer(to: &value) { valuePtr in
    return valuePtr.withMemoryRebound(to: Byte.self, capacity: totalBytes) { reboundPtr in
      return Array(UnsafeBufferPointer(start: reboundPtr, count: totalBytes))
    }
  }
}
4
Nathan Kot

Voici ma version mise à jour de la solution d'origine.

/// input: array of bytes 
/// -> get pointer to byte array (UnsafeBufferPointer<[Byte]>)
/// -> access its base address
/// -> rebind memory to target type T (UnsafeMutablePointer<T>)
/// -> extract and return the value of target type
func binarytotype <T> (_ value: [Byte], _: T.Type) -> T
{
    return value.withUnsafeBufferPointer {
        $0.baseAddress!
          .withMemoryRebound(to: T.self, capacity: 1) {
            $0.pointee
        }
    }
}

/// input type: value of type T
/// -> get pointer to value of T
/// -> rebind memory to the target type, which is a byte array
/// -> create array with a buffer pointer initialized with the     source pointer
/// -> return the resulted array
func typetobinary <T> (_ value: T) -> [Byte]
{
    var mv : T = value
    let s : Int = MemoryLayout<T>.size
    return withUnsafePointer(to: &mv) {
        $0.withMemoryRebound(to: Byte.self, capacity: s) {
            Array(UnsafeBufferPointer(start: $0, count: s))
        }
    }
}

PS: N'oubliez pas de remplacer Byte par UInt8.

4
segabor

Les réponses acceptées sont dangereuses car la MemoryLayout vous fournit la taille du type statique T!

Pour contourner le problème, vous devez créer un protocole personnalisé et demander Self dans celui-ci:

protocol ByteConvertible {}

extension ByteConvertible {

    func toBytes() -> [UInt8] {

        let capacity = MemoryLayout<Self>.size
        var mutableValue = self
        return withUnsafePointer(to: &mutableValue) {

            return $0.withMemoryRebound(to: UInt8.self, capacity: capacity) {

                return Array(UnsafeBufferPointer(start: $0, count: capacity))
            }
        }
    }
}

J'ai déjà mentionné que les réponses acceptées sont dangereuses et voici un exemple:

let num = UInt8(42)
MemoryLayout.size(ofValue: num) //=> 1 byte as expected
let any: Any = num
MemoryLayout.size(ofValue: any) //=> 32 bytes which is what will happen in the generic functions from the all the answers

Swift 3.0

4
DevAndArtist
func byteArray<T>(_ value: T) -> [UInt8] {
    var value = value
    var initialArray = withUnsafeBytes(of: &value) { Array($0) }

    initialArray.reverse()
    var count = initialArray.count
    while initialArray.first == 0 && count > 1 {
        initialArray[0...count - 2] = initialArray[1...count - 1]
        count -= 1
    }
    if initialArray[0] >= 128 {
        var newArray = [UInt8](repeating: 0, count: count + 1)
        newArray[0] = UInt8(0)
        newArray[1...count] = initialArray[0...count - 1]
        return newArray
    } else {
        return Array(initialArray[0...count - 1])
    }
}
1
Bogdan Razvan

La méthode ci-dessus fonctionne, en utilisant Swift 2 mais, j'ai découvert une méthode beaucoup plus simple et plus rapide pour effectuer cette conversion et vice versa:

func binarytotype <T> (value: [UInt8], _: T.Type) -> T
{
    return value.withUnsafeBufferPointer
    {
        return UnsafePointer<T>($0.baseAddress).memory
    }
}

func typetobinary <T> (var value: T) -> [UInt8]
{
    return withUnsafePointer(&value)
    {
        Array(UnsafeBufferPointer(start: UnsafePointer<UInt8>($0), count: sizeof(T)))
    }
}

let a: Double = 0.25
let b: [UInt8] = typetobinary(a) // -> [0, 0, 0, 0, 0, 0, 208, 63]
let c = binarytotype(b, Double.self) // -> 0.25

Je l'ai testé avec Xcode 7.2 dans la cour de récréation.

1
j.s.com