问题
I've been working on some vDSP code and I have come up against an annoying problem. My code is cross platform and hence uses std::complex to store its complex values.
Now I assumed that I would be able to set up an FFT as follows:
DSPSplitComplex dspsc;
dspsc.realp = &complexVector.front().real();
dspsc.imagp = &complexVector.front().imag();
And then use a stride of 2 in the appropriate vDSP_fft_* call.
However this just doesn't seem to work. I can solve the issue by doing a vDSP_ztoc but this requires temporary buffers that I really don't want hanging around. Is there any way to use the vDSP_fft_* functions directly on interleaved complex data? Also can anyone explain why I can't do as I do above with a stride of 2?
Thanks
Edit: As pointed out by Bo Persson the real and imag functions don't actually return a reference.
However it still doesn't work if I do the following instead
DSPSplitComplex dspsc;
dspsc.realp = ((float*)&complexVector.front()) + 0;
dspsc.imagp = ((float*)&complexVector.front()) + 1;
So my original question still does stand :(
回答1:
The std::complex functions real()
and imag()
return by value, they do not return a reference to the members of complex.
This means that you cannot get their addresses this way.
回答2:
This is how you do it.
const COMPLEX *in = reinterpret_cast<const COMPLEX*>(std::complex);
Source: http://www.fftw.org/doc/Complex-numbers.html
EDIT:
To clarify the source; COMPLEX and fftw_complex use the same data layout (although fftw_complex uses double
and COMPLEX float
)
来源:https://stackoverflow.com/questions/7538264/using-stdcomplex-with-iphones-vdsp-functions