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Update kiss-fft to 1.4.0 and disable OpenMP for it.

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wolfbeast 2018-06-07 14:44:14 +02:00 • committed by Roy Tam
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51
media/kiss_fft/README
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@ -44,30 +44,6 @@ The core fft and most tools/ code can be compiled to use float, double,
Q15 short or Q31 samples. The default is float.
BACKGROUND:
I started coding this because I couldn't find a fixed point FFT that didn't
use assembly code. I started with floating point numbers so I could get the
theory straight before working on fixed point issues. In the end, I had a
little bit of code that could be recompiled easily to do ffts with short, float
or double (other types should be easy too).
Once I got my FFT working, I was curious about the speed compared to
a well respected and highly optimized fft library. I don't want to criticize
this great library, so let's call it FFT_BRANDX.
During this process, I learned:
1. FFT_BRANDX has more than 100K lines of code. The core of kiss_fft is about 500 lines (cpx 1-d).
2. It took me an embarrassingly long time to get FFT_BRANDX working.
3. A simple program using FFT_BRANDX is 522KB. A similar program using kiss_fft is 18KB (without optimizing for size).
4. FFT_BRANDX is roughly twice as fast as KISS FFT in default mode.
It is wonderful that free, highly optimized libraries like FFT_BRANDX exist.
But such libraries carry a huge burden of complexity necessary to extract every
last bit of performance.
Sometimes simpler is better, even if it's not better.
FREQUENTLY ASKED QUESTIONS:
Q: Can I use kissfft in a project with a ___ license?
A: Yes. See LICENSE below.
@ -78,10 +54,6 @@ FREQUENTLY ASKED QUESTIONS:
2) mixed build environment -- all code must be compiled with same preprocessor
definitions for FIXED_POINT and kiss_fft_scalar
Q: Will you write/debug my code for me?
A: Probably not unless you pay me. I am happy to answer pointed and topical questions, but
I may refer you to a book, a forum, or some other resource.
PERFORMANCE:
(on Athlon XP 2100+, with gcc 2.96, float data type)
@ -111,24 +83,25 @@ UNDER THE HOOD:
FFTs in parallel (packed into real&imag), and then combines them via twiddling. The result is
nfft/2+1 complex frequency bins from DC to Nyquist. If you don't know what this means, search the web.
The fast convolution filtering uses the overlap-scrap method, slightly
modified to put the scrap at the tail.
The fast convolution filtering uses the overlap-scrap method, slightly modified to put
the scrap at the tail.
LICENSE:
Revised BSD License, see COPYING for verbiage.
BSD-3-Clause License, see LICENSE for verbiage.
Basically, "free to use&change, give credit where due, no guarantees"
Note this license is compatible with GPL at one end of the spectrum and closed, commercial software at
the other end. See http://www.fsf.org/licensing/licenses
A commercial license is available which removes the requirement for attribution. Contact me for details.
TODO:
This fork of the library always requires attribution. Contrary to the original version of the library,
written by a sole developer, no exception to the license is available that allows use without attribution
because of contributed code.
TO-DO:
*) Add real optimization for odd length FFTs
*) Document/revisit the input/output fft scaling
*) Make doc describing the overlap (tail) scrap fast convolution filtering in kiss_fastfir.c
*) Test all the ./tools/ code with fixed point (kiss_fastfir.c doesn't work, maybe others)
AUTHOR:
Mark Borgerding
Mark@Borgerding.net
AUTHORS:
Mark Borgerding (mark@borgerding.net)
Mark Straver BASc (moonchild@palemoon.org)