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Casting between two structs in C (CUDA)

The CUDA library effectively defines its own complex number data type, cuComplex, as follows:

struct __builtin_align__(8) float2
{
float x, y;
};
typedef float2 cuFloatComplex;
typedef cuFloatComplex cuComplex;

I am already using my own complex data type:

typedef struct { float re; float im; } complex;

and I wish to be able to cast between the two. Here's an example of what I'm currently trying:

cuComplex cu_data;
...
complex c_data;
c_data = (complex)cu_data;

but I'm getting the (nvcc) error:

'no suitable user-defined conversion from "cuComplex" to "complex" exists'.

So how do I do this? Equivalently: is there a way to do a typedef, but to simply rename the members of that struct? (ie rename 'x' to 're', 'y' to 'im')?

Thanks!

jkr

You could provide your own operator, e.g.

  struct /*__builtin_align__(8)*/ float2
  {
    float x, y;
  };
  typedef float2 cuFloatComplex;
  typedef cuFloatComplex cuComplex;

 typedef struct  { float re; float im; operator cuComplex();} complex;

 complex::operator cuComplex() {

   cuComplex out;

   out.x = re;
   out.y = im;

   return out;
 }

  int main () {

  cuComplex out;
  complex in;

  out = (cuComplex) in;

  return 0;
  }

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jkr

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sridhard

Hi,

Try using pointers . This will assign/point the correponding values. Note sure whether this helps

cuComplex cu_data = (cuComplex *) malloc(sizeof(cuComplex ));
...
complex *c_data;
c_data = (complex*)cu_data;

You can delete any one pointer later .

InteractiveMind

ASKER

Thank you, both. I think I should mention that I am in fact casting pointers/arrays of such types in my code (but I get the same problem).

@jkr, would your method work for casting pointers? (I can't test it at the moment). If so, my code needs to be as fast as possible, so given that I'm going to need to do [probably] millions of such casts per second, would it be quicker to just do a typedef:

typedef cuComplex complex;

and then a global search and replace of '.re' with '.x' etc? (I'm reluctant to do so)

Also, can you think of any reason why what I'm already doing wouldn't work? Is it the __builtin_align__(8) that's causing problems?

jkr

>>@jkr, would your method work for casting pointers?

If you use the indirecton appropriately - yes.

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Infinity08

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ikework

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ikework

The safest strategy is to use only cuda's struct in the first place, also in your code, so there is no cast needed anymore.

ambience

>> so given that I'm going to need to do [probably] millions of such casts per second, would it be quicker to just do a typedef:

My vote -> YES

ikework

@ambience, did you consider the different alignments as previous posts said?

ikework

@ambience, sorry I misunderstood your post, I thought you were suggesting just cast anyway, nevermind :)

soscpd

Hi

Your answer is a function ponter. There (in the function) you read/write cuComplex/complex structs anyway you like.

Rafael

InteractiveMind

ASKER

Thanks