So I've changed my mind about the design of my kernel density estimation
lib that needed an FFT. I now no longer have an immediate use for an
FFT in D. I also gave up on trying to translate kiss_fft because the
code is so difficult to follow that if it doesn't work I'll be at a loss
to debug it.
However, in the process of prototyping I wrote a very basic FFT lib. It
only handles power of two sizes. It handles generic random-access
ranges of complex inputs using std.complex, or pure real inputs of any
builtin numeric type. It does not include any cache optimizations and
takes about 1.7 seconds to do a double[] -> Complex!double FFT of size
2^20 on my machine Athlon 64 X2 5200+. (I haven't benchmarked other
libs so I have no idea how fast or slow this really is). Support for
inverse FFTs can be trivially added, and definitely will be if this is
contributed to Phobos.
As I am no longer going to use FFTs in my kernel density lib, improving
this FFT code will be bumped down my hacking to-do list. Does what I
have now sound better than nothing by a large enough margin to warrant
inclusion in std.numeric, or does it sound too primitive to be widely
useful? If it sounds worth including I'll clean up/document the code
and send it to the mailing list for review. If it sounds too primitive,
I'll just scrap it.
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