iOS: using vDSP functions in 64bit

Question

In iOS, I have a function call that depends on vDSP_vgathr, a member of Apple's Accelerate framework:

int pix = image.size.height * image.size.width;
float * array = (float *)malloc(sizeof(float) * pix * 4);
float * colorPlane = (float *)malloc(sizeof(float) * pix);
float * y_r = (float *)malloc(sizeof(float) * pix)
int * malloc(sizeof(int) * pix)

vDSP_vgathr(colorPlane, (const vDSP_Length *)idx, 1, y_r, 1, (int)(rate*pix));

I've seen an SO question that relating to the error I get, EXC_I386_GPFLT, and 64 bit systems and non-canonical pointers. The solution (and another one) I've seen suggest including tgmath.h, but when used (with a successful compile), it does nothing and I still get EXC_I386_GPFLT.

I've tried a host of other potential solutions including typecasting various objects and different function calls. How can I do I make this function call work with the 64 bit architecture?

Answer 1

The docs for vDSP_vgathr say it's defined as

void vDSP_vgathr (
   float *__vDSP_A,
   vDSP_Length *__vDSP_B,
   vDSP_Stride __vDSP_J,
   float *__vDSP_C,
   vDSP_Stride __vDSP_K,
   vDSP_Length __vDSP_N
);

You're passing an int into that function and vDSP_Length is defined as unsigned long. So, pass an unsigned long in:

unsigned long * idxSend = (unsigned long *)malloc(sizeof(unsigned long) * N);
for (i=0; i<N; i++) idxSend[i] = (unsigned long)idx[i];
vDSP_vgathr(..., idxSend, ...);

That solves your problem.