35 lines
1.6 KiB
Plaintext
35 lines
1.6 KiB
Plaintext
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ls_fft description:
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This package is intended to calculate one-dimensional real or complex FFTs
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with high accuracy and good efficiency even for lengths containing large
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prime factors.
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The code is written in C, but a Fortran wrapper exists as well.
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Before any FFT is executed, a plan must be generated for it. Plan creation
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is designed to be fast, so that there is no significant overhead if the
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plan is only used once or a few times.
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The main component of the code is based on Paul N. Swarztrauber's FFTPACK in the
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double precision incarnation by Hugh C. Pumphrey
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(http://www.netlib.org/fftpack/dp.tgz).
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I replaced the iterative sine and cosine calculations in radfg() and radbg()
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by an exact calculation, which slightly improves the transform accuracy for
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real FFTs with lengths containing large prime factors.
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Since FFTPACK becomes quite slow for FFT lengths with large prime factors
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(in the worst case of prime lengths it reaches O(n*n) complexity), I
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implemented Bluestein's algorithm, which computes a FFT of length n by
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several FFTs of length n2>=2*n-1 and a convolution. Since n2 can be chosen
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to be highly composite, this algorithm is more efficient if n has large
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prime factors. The longer FFTs themselves are then computed using the FFTPACK
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routines.
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Bluestein's algorithm was implemented according to the description at
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http://en.wikipedia.org/wiki/Bluestein's_FFT_algorithm.
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Thread-safety:
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All routines can be called concurrently; all information needed by ls_fft
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is stored in the plan variable. However, using the same plan variable on
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multiple threads simultaneously is not supported and will lead to data
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corruption.
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