[Newbies] [Q] How can I write down my FFI method for this C function? (Sorry if duplicated)

[Levente Uzonyi]

On Fri, 4 Mar 2011, Sungjin Chun wrote:

> Hi,
>
> The C function is like this;
>
> BOOL ComputeVector (int startIdx, int endIdx, double *inputSeries, int
> duration, int *outBeginIdx, int *outNBElement, double *outSeries);
>
> My trial method is
>
> apiComputeVectorWith: startIdx with: endIdx with: input duration:
> duration with: outBeginIdx with: outNBElement out: out
>   <cdecl: bool 'ComputeVector' (long long double* long long* long* double*)>
>
> But with these input variable, I got error with "could not coerce arguments".
>
> input := ((1 to: 100) collect: [ :i | i ]) asFloatArray.
> startIdx := 0.
> endIdx := input size - 1.
> duration := 4.
> outBeginIndx := IntegerArray new: 1.
> outNBElement := IntegerArray new: 1.
> out := FloatArray new: input size.
> computer apiComputeVectorWith: startIdx with: endIdx with: input
> duration: duration with: outBeginIdx with: outNBElement out: out.
>
> Can anyone help me on this? Thank you in advance.

The cause of the error is that FloatArray is an array of 32-bit floats 
(unlike Float which is a 64-bit floating point number aka double).
Your method expects double*. AFAIK there's no Smalltalk type that matches 
double*, so you have to coerce the arguments yourself.
Here's how you can do it (I didn't try it, so it may not work):

"We will pass WordArrays, since Floats consist of two words, which makes 
coercion easy."

apiComputeVectorWith: startIdx with: endIdx with: input duration:
duration with: outBeginIdx with: outNBElement out: out
    <cdecl: bool 'ComputeVector' (long long long* long long* long* 
long*)>

input := WordArray new: 200.
1 to: 100 do: [ :i |
 	| float |
 	float := i asFloat.
 	input at: 2 * i - 1 put: (float at: 1).
 	input at: 2 * i put: (float at: 2) ]
startIdx := 0.
endIdx := input size - 1.
duration := 4.
outBeginIndx := IntegerArray new: 1.
outNBElement := IntegerArray new: 1.
out := WordArray new: input size.
computer apiComputeVectorWith: startIdx with: endIdx with: input duration: duration with: outBeginIdx with: outNBElement out: out.
out := out pairsCollect: [ :word1 :word2 |
 	(Float new: 2)
 		at: 1 put: word1;
 		at: 2 put: word2;
 		yourself ]


Levente

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