Casting parameters to make Swift compile with vDSP API - ios

Question

I am running into some issues trying to use the Accelerate framework with vDSP API from Swift. Obviously I am doing something wrong although the compiler gives me all sorts of warnings
var srcAsFloat:CConstPointer<CFloat> = CFloat[](count: Int(width*height), repeatedValue: 0)
var dstAsFloat = CFloat[](count: Int(width*height), repeatedValue: 0)
if shouldClip {
var min:CFloat = 0.0
var max:CFloat = 255.0
var l:vDSP_Stride = Int(width*height)
vDSP_vclip(CConstPointer<CFloat>(&dstAsFloat), vDSP_Stride(1), CConstPointer<CFloat>(&min), CConstPointer<CFloat>(&max), CMutablePointer<CFloat>(&dstAsFloat), vDSP_Stride(1), l)
}
The error:
error: could not find an overload for 'init' that accepts the supplied arguments
vDSP_vclip(CConstPointer<CFloat>(&dstAsFloat),
vDSP_Stride(1),
CConstPointer<CFloat>(&min),
CConstPointer<CFloat>(&max),
CMutablePointer<CFloat>(&dstAsFloat),
vDSP_Stride(1),
l) –
I've tried to cast the heck out of it but so far, no luck.

Answer 1

Okay, I figured out a (probably sub-optimal) solution. I decided to bridge to Objective-C (and used a slightly different function).
main.swift
import Foundation
func abs(x: matrix) -> matrix{
let N = x.count
var arg1 = NSArray(array: x)
var yy = abs_objc(arg1, CInt(N))
var y = zeros(N)
for i in 0..N{
y[i] = Double(yy[i])
}
return y
abs_objc.m
#import <Accelerate/Accelerate.h>
double* abs_objc(NSArray * x, int N){
// converting input to double *
double * xx = (double *)malloc(sizeof(double) * N);
for (int i=0; i<[x count]; i++) {
xx[i] = [[x objectAtIndex:i] doubleValue];
}
// init'ing output
double * y = (double *)malloc(sizeof(double) * N);
for (int i=0; i<N; i++){
y[i] = 0;
}
vDSP_vabsD(xx,1,y,1,N);
return y;
}
swix-Bridging-Header.h
#import <Foundation/Foundation.h>
double* abs_objc(NSArray * x, int N);

Answer 2

I've been working with vDSP to just create a general matrix language.
I have found this way to be the easiest to get the correct pointer types.
Hopefully you find it useful (this might not be optimal either but a start).
import Accelerate
func myFunction(width:Float, height:Float) {
var dstAsFloat = CFloat[](count: Int(width*height), repeatedValue: 0)
var min:CFloat = 0.0
var max:CFloat = 255.0
func vclipPointerConversion(dstAsFloat:CMutablePointer<CFloat>) {
vDSP_vclip(CConstPointer<CFloat>(nil,dstAsFloat.value), vDSP_Stride(1),
&min, &max, dstAsFloat, vDSP_Stride(1), CUnsignedLong(width*height))
}
vclipPointerConversion(&dstAsFloat)
//...
// return whatever you wanted
}

Answer 3

I got it to work with a few tweaks. Notice the first param doesn't have an ampersand (CConstPointer). However the second one does (I use the same pointer for src & dst). I also replaced the casting (necessary) of values. You need to use CFloats for ceiling values. Here is the code:
let width: UInt = CGBitmapContextGetWidth(context)
let height: UInt = CGBitmapContextGetHeight(context)
var dstAsFloat = CFloat[](count: Int(width*height), repeatedValue: 0)
if shouldClip {
var min:CFloat = 0.0
var max:CFloat = 255.0
vDSP_vclip(dstAsFloat, CLong(1), &min, &max, &dstAsFloat, CLong(1), UInt(width*height))
}