如何使用 vDSP / Accelerate in swift for iOS 逐元素计算向量的平方根

Question

我有一个类似于 [Float](repeating: 1.0, count: 42000) 的向量，我想使用 Accelerate 框架计算每个元素的平方根，但不存在与 vDSP_vsqrt 中所述相反的函数=14=]。我应该怎么做？

Answer 1

似乎正确的调用函数是 vvsqrtf 来自 vForce。

这里是 the documentation 的例子，它的用法：

var x: [Float] = [100, 10000, 64, 144]
var y = [Float](repeating: 0, count: x.count)
var n = Int32(x.count)

vvsqrtf(&y, &x, &n)

print(y) // [10.0, 100.0, 8.0, 12.0]

请注意，您还可以计算平方根 "in place" :

var data = [Float](repeating: 25.0, count: input.count)
let n = Int32(data.count)

vvsqrtf(&data, data, &n)

Answer 2

我建议制作辅助函数来包装 vvsqrtf，以公开更 Swift 友好的 API:

import Accelerate

extension Array where Element == Float {
    func squareRootedElements() -> [Float] {
        if self.isEmpty { return [] }

        var output = Array(repeating: 0, count: self.count)
        var count = Int32(self.count)

        vvsqrtf(&output, self, &count)

        return output
    }

    mutating func squareRootElements() {
        if self.isEmpty { return }

        var count = Int32(self.count)

        vvsqrtf(&self, self, &count)
    }
}

var squares = stride(from: 0 as Float, through: 10, by: +1).map { [=10=] * [=10=] }
print(squares)
print(squares.squareRootedElements())

Answer 3

vForce Swift 覆盖使语法更简单：

vForce.sqrt(vector: AccelerateBuffer)

看看：https://github.com/apple/swift/blob/master/stdlib/public/Darwin/Accelerate/vForce_Operations.swift

...和...

https://developer.apple.com/videos/play/wwdc2019/718/

如何使用 vDSP / Accelerate in swift for iOS 逐元素计算向量的平方根

How to compute the square root of a vector elementwise using vDSP / Accelerate in swift for iOS

ios

accelerate-framework

swift