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From: Daniel Andor <da209@cam.ac.uk>
Reply-To: Daniel.Andor@physics.org
To: Caml List <caml-list@inria.fr>
Subject: [Caml-list] C -> CAML linking: loosing values in arrays??
Date: Sat, 11 Jan 2003 19:07:51 +0000
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Hi All,

I'm trying to call a numerical routine I wrote in caml from c.  I'm using the 
-output-obj option of ocamlopt, and have stub functions in c that convert the 
parameters.  Since it's for numerics, I want to pass arrays of doubles.  So I 
use make_float_array from below to convert a 4dimensional doube array into a 
value ready to be passed to caml.

value make_float(double *d) 
{ 
  /* value of d intentionally ignored while we debug... */
  return copy_double(0.0);
}

#define NUM_DIMS 4
value make_float_array(double *ds)
{
  int i;
  double* p[NUM_DIMS+1];
  p[NUM_DIMS]=NULL;
  for (i=0; i<NUM_DIMS; i++)
    p[i] = &(ds[i]);
  return alloc_array(make_float,p);
}

The caml code gets called correctly, and from within it I can see that the 
length or the arrays and the content are bogus (they come out length 2, not 
4, with the first elements looking like this: 62.6141, not 0.0).

If I pass a non-array double using copy_double(), it works and I get the 
correct number on the other side.

Any ideas as to where I've gone wrong?

Thanks,
Daniel.
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