Swift - Convolution with Accelerate Framework

Question

I'm trying to do 1D convolution with Accelerate framework.

I can make it work but it seems like something goes wrong after a few experiments.

Here is my code:

import Accelerate

var N = 10000
var M = 10
var convN = N + M - 1

var xf = [Float](count:N, repeatedValue:0.0)
var yf = [Float](count:M, repeatedValue:0.0)

for i in 0..<N {
    xf[i] = Float(i+1)
}
for i in 0..<M {
    yf[i] = Float(i+1)
}

var outputf = [Float](count:convN, repeatedValue:0.0)

// padding zero
xf = [Float](count:convN-N, repeatedValue:0.0) + xf

var ptr_xf = UnsafePointer<Float>(xf)
var ptr_yf = UnsafePointer<Float>(yf).advancedBy(yf.count-1)

vDSP_conv(ptr_xf, 1, ptr_yf, -1, &outputf, 1, vDSP_Length(convN), vDSP_Length(M))
print("[Float]: \(outputf)")

I compile and run it with different N and M .

Then I check the result with the result from python package numpy .

Sometime it looks great but sometime it just give me some weird result like:

( N =6, M =3)

Correct: [1.0, 4.0, 10.0, 16.0, 22.0, 28.0, 27.0, 18.0]

Result I get: [1.0, 4.0, 10.0, 16.0, 22.0, 28.0, 2.23692e+08, 4.47384e+08]

Do I miss anything here? I can not figure out what I've done wrong.

Answer 1

Does it have something to do with your Swift Version ? I am using V 3.0.2 and the following code works well for me.

import Accelerate

var N = 6
var M = 3

var convN = N + M - 1

var xf = [Float](repeating:0.0, count:N)
var yf = [Float](repeating:0.0, count:M)

for i in 0..<N {
    xf[i] = Float(i+1)
}
for i in 0..<M {
    yf[i] = Float(i+1)
}

var outputf = [Float](repeating:0.0, count:convN)

// padding zero
xf = [Float](repeating:0.0, count:convN-N) + xf

var ptr_xf = UnsafePointer<Float>(xf)
var ptr_yf = UnsafePointer<Float>(yf).advanced(by: yf.count-1)


vDSP_conv(ptr_xf, 1, ptr_yf, -1, &outputf, 1, vDSP_Length(convN), vDSP_Length(M))

print("[Float]: \(outputf)") // [Float]: [1.0, 4.0, 10.0, 16.0, 22.0, 28.0, 27.0, 18.0]