Swift Data to Int array

Question

I'd like to access the raw bytes in Data as an array of numeric types for quick parsing. I have lots of data to parse, so I'm looking for efficiency. Data is a mix of shorts, ints, longs, and doubles.

The below code seems to work and be fast, but I'm getting deprecated warning: 'withUnsafeBytes' is deprecated

I can't figure out the updated way to treat the underlying bytes as an array of numbers for quick lookup.

    var data: Data = ...
            
    // create "virtual" arrays of different types to directly access bytes (without copying bytes)
    
    let ushortArray: [UInt16] = data.withUnsafeBytes {
        [UInt16](UnsafeBufferPointer(start: $0, count: data.count/2))
    }
    let intArray: [Int32] = data.withUnsafeBytes {
        [Int32](UnsafeBufferPointer(start: $0, count: data.count/4))
    }

    // Access data simply
    var i1: UInt16 = ushortArray[0]
    var i2: Int32 = intArray[1]

P.S. I'm not concerned with big/little endian

https://stackoverflow.com/questions/55378409/swift-5-0-withunsafebytes-is-deprecated-use-withunsafebytesr ? I guess, I'm no sure yet that it's be then in the closure `{ $0.load(as: [UInt16].self) }`, to test... — Larme, Mar 05 '22 at 18:35
@Larme This only works for `UInt16.self`. For array AFAIR you need `bindMemory` — Leo Dabus, Mar 05 '22 at 19:12

Leo Dabus · Accepted Answer · 2022-03-05T20:33:43.477

If you want to load it as an Array what you need is to use UnsafeRawBufferPointer bindMemorymethod to the type you want. you can also extend ContiguousBytes to make a generic method and simplify your syntax:

Note: if you are planing to get a subsequence of your data make sure to do NOT subscript the data to avoid misaligned errors. You need to use Data subdata method instead.

extension ContiguousBytes {
    func objects<T>() -> [T] { withUnsafeBytes { .init($0.bindMemory(to: T.self)) } }
    var uInt16Array: [UInt16] { objects() }
    var int32Array: [Int32] { objects() }
}

extension Array {
    var data: Data { withUnsafeBytes { .init($0) } }
}

Usage:

let uInt16Array: [UInt16] = [.min, 1, 2, 3, .max]  // [0, 1, 2, 3, 65535]
let int32Array: [Int32] = [.min, 1, 2, 3, .max]    // [-2147483648, 1, 2, 3, 2147483647]

let uInt16ArrayData = uInt16Array.data  // 10 bytes
let int32ArrayData = int32Array.data    // 20 bytes

let uInt16ArrayLoaded = uInt16ArrayData.uInt16Array  // [0, 1, 2, 3, 65535]
let int32ArrayLoaded = int32ArrayData.int32Array       // [-2147483648, 1, 2, 3, 2147483647]

// Access data simply
let i1 = uInt16ArrayLoaded[0]   //  UInt16 0
let i2 = int32ArrayLoaded[0]    // Int32 -2147483648
let i3 = uInt16ArrayLoaded[4]   //  UInt16 65535
let i4 = int32ArrayLoaded[4]    // Int32 2147483647

Swift Data to Int array

1 Answers1