| Author |
Message |
Heureka
Guest
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 Posted:
Mon Dec 26, 2005 1:15 am Post subject:
FFTW 3.01 and C++ |
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Hi,
I hope this is not off topic!
I'm trying to make use of the FFTW library (V3.01) but I have some
difficulties working out the data types which comes with the library - and
possibly the coding too! Below I have pasted in my current source code which
should calculate the FFT of real input data. The input is a sinusoid signal
and I'm looking for non-zero data in the output vector but all I get is
zeros. I'm fairly green in terms of c++ programming so there might be some
really basic problems with my code. Furthermore, I'm not really sure how to
extract data from the output vector (a vector of the fftw_complex) Does
anyone know how to do this?
Cheers
Thomas
// FFT specific
int N = 256;
// Input test signal
double input[256];
char txt[256];
for(int indx=0; indx<256; indx++)
{
input[indx]=cos(2.f*22.f/7.f*1000.f*(indx/20000.f));
sprintf(txt,"sample[%d]= %f",indx,input[indx]);
OutputDebugString(txt);
}
double *in;
fftw_complex *out;
fftw_plan p;
in = (double *)fftw_malloc(sizeof(double) * N);
out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N);
p = fftw_plan_dft_r2c_1d(N, in, out, FFTW_MEASURE);
fftw_execute(p); /* repeat as needed */
fftw_destroy_plan(p);
in = input;
fftw_free(in);
fftw_free(out);
for(int indx=0; indx<256; indx++)
{
sprintf(txt,"re[%d]=%f,& im[%d]=%f", indx, &out[indx][0], indx,
&out[indx][1]);
OutputDebugString(txt);
sprintf(txt,"re[%d]=%f,& im[%d]=%f", indx, out[indx][0], indx,
out[indx][1]);
OutputDebugString(txt);
} |
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Heureka
Guest
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| Posted:
Mon Dec 26, 2005 1:15 am Post subject:
Re: FFTW 3.01 and C++ |
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Hi ,
I found a bug so here is the sourcecode that still isn't working! :)
// FFT specific
int N = 256;
// Input test signal
double input[256];
char txt[256];
for(int indx=0; indx<256; indx++)
{
input[indx]=cos(2.f*22.f/7.f*1000.f*(indx/20000.f));
sprintf(txt,"sample[%d]= %f",indx,input[indx]);
OutputDebugString(txt);
}
double *in;
fftw_complex *out;
fftw_plan p;
in = (double *)fftw_malloc(sizeof(double) * N);
out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N);
in = input;
p = fftw_plan_dft_r2c_1d(N, in, out, FFTW_MEASURE);
fftw_execute(p); /* repeat as needed */
for(int indx=0; indx<256; indx++)
{
sprintf(txt,"re[%d]=%f,& im[%d]=%f", indx, &out[indx][0], indx,
&out[indx][1]);
OutputDebugString(txt);
}
fftw_destroy_plan(p);
fftw_free(in);
fftw_free(out); |
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Heureka
Guest
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| Posted:
Mon Dec 26, 2005 5:15 pm Post subject:
Re: FFTW 3.01 and C++ |
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"William C Bonner" <wbonner@wimsworld.com> wrote in message
news:1135608574.878347.126730@g44g2000cwa.googlegroups.com...
| Quote: | Why do people use the fftw library routines on a dsp?
I would assume that using DSP optimized libraries would get faster
results, and be more optimized for memory access as well.
I use fftw on the PC, for general purpose FFT calculations, but in that
case, having source code that compiles cross platform is helpful. Also,
I have not found better optimized distributable C/C++ FFT routines.
Hi, |
Thanks for your reply. The transform is now working correctly. I found the
bug this morning :)
Cheers
Thomas |
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William C Bonner
Guest
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| Posted:
Mon Dec 26, 2005 5:15 pm Post subject:
Re: FFTW 3.01 and C++ |
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I've not uaed the latest version of fftw, but it appears that you are
missing several steps..
You create your raw data in the array input, but I never see you copy
that to the array "in" that you are using for the fftw routines.
I never see you use the "out" array before you free it up again.
(actually you use the array immediately after you free it, so I'm
surprised that you don't get some sort of exception.) |
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William C Bonner
Guest
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| Posted:
Mon Dec 26, 2005 5:15 pm Post subject:
Re: FFTW 3.01 and C++ |
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Why do people use the fftw library routines on a dsp?
I would assume that using DSP optimized libraries would get faster
results, and be more optimized for memory access as well.
I use fftw on the PC, for general purpose FFT calculations, but in that
case, having source code that compiles cross platform is helpful. Also,
I have not found better optimized distributable C/C++ FFT routines. |
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Michel Rouzic
Guest
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| Posted:
Tue Dec 27, 2005 5:15 pm Post subject:
Re: FFTW 3.01 and C++ |
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Heureka wrote:
| Quote: | in = (double *)fftw_malloc(sizeof(double) * N);
out = (fftw_complex *)fftw_malloc(sizeof(fftw_complex) * N);
|
Idk if it's the same with fftw_malloc as with the regular malloc, but
you should not cast the result of a malloc(). you have to include
stdlib.h (if i remember good)
btw, you say it's C++, but you can call that C, cuz all you type here
was in C |
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