Re: [C2hs] Marshal Haskell list into monolithic arrays

18 Aug 2006

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From: Udo Stenzel 
To: zhu Jun 
Subject: Re: [C2hs] Marshal Haskell list into monolithic arrays
Date: Thu, 17 Aug 2006 17:17:21 +0200
zhu Jun wrote:
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There is a 'newArray' operation in MarshallArray to marshal Haskell
Hi Udo and Duncan,

Yes, I made a mistake in C syntax. 
Now, I call the function in Haskell like this:
 -------------------------
lowPassFilter :: [CFloat] -> CFloat
lowPassFilter fs =  (unsafePerformIO (lowPassFilterWrap fs))
    where lowPassFilterWrap :: [CFloat] -> IO CFloat
	  lowPassFilterWrap fs = do
	        mfs <- newArray fs
                fsP2 <- malloc
                r <- f_lowPassFilter mfs fsP2
                returnF <- peek fsP2
                return returnF

foreign import ccall "static fmr.h lowPassFilter"
  f_lowPassFilter :: Ptr (CFloat) -> Ptr (CFloat) -> IO (())

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and the C function is defined as:
////////////////////////
void lowPassFilter(float *buff, float *sum)
{

// Work part
  for (i = 0; i < NUM_TAPS; i++)
  {
    printf("buff %d = %f \n", i, *(buff++));
    *sum += *(buff++) * coeff[i];
  }
}
////////////////////////

It works well! Thank you so much!

Best wishes,

Yours,
  Jun

list,
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The C function looks like:
////////////////////
void lowPassFilter(float *fs[10], float *sum)
This function doesn't take (a pointer to) an array of floats, but (a
pointer to) an array of pointers to floats, which I doubt was your
intention.  You need help programming in C, not help using C2HS.  Try a
book or ask in news:comp.lang.c
Udo.

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