mirror/kissfft
1
0
Fork 0
mirror of https://github.com/mborgerding/kissfft.git synced 2025-07-18 21:14:24 -04:00
Code Issues Packages Projects Releases Wiki Activity

getting ready for next release

Browse Source
This commit is contained in:
Mark Borgerding
2003-10-26 04:07:32 +00:00
parent 52b4b9ab5c
commit 1db3d91ee5
9 changed files with 68 additions and 314 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
README
View File

@ -1,4 +1,4 @@
KISS FFT - A power-of-two Fast Fourier Transform based up on the principle,
KISS FFT - A mixed-radix Fast Fourier Transform based up on the principle,
"Keep It Simple, Stupid."
There are many great fft libraries already around. Kiss FFT is not trying
@ -26,8 +26,8 @@ two functions you'll need to use. Code definitions are in kiss_fft.c, along
with sample usage code.
The code can be easily recompiled to work with 16bit fixed point data,
or various floating point types. The default is float.
The code can be compiled to use float, double or 16bit short samples.
The default is float.
BACKGROUND:
@ -35,22 +35,23 @@ 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,
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 wanted to get some performance numbers against
a well respected and highly optimized fft library. I don't want to criticize
this great library, so let's call it FFT_BRANDX.
this great library, so let's call it FFT_BRANDX.
During this process, I learned:
1. FFT_BRANDX has 500 times as many lines of code as Kiss
(and that's just the C code).
2. It took me an embarrassingly long time to get FFT_BRANDX working.
3. FFT_BRANDX is almost 3 times faster than Kiss
3. A simple program using FFT_BRANDX is 500K. A similar program using kiss_fft is 18k.
4. FFT_BRANDX is about 3-4 times faster than Kiss
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.
last bit of performance.
Sometimes simpler is better, even if it's not better.
@ -62,13 +63,12 @@ PERFORMANCE:
DO NOT:
... use Kiss if you need the absolute fastest fft in the world
... use Kiss if you need mixed radix FFTs
... ask me to add features that will bloat the code
UNDER THE HOOD:
Kiss uses a complex-only, frequency decimation, radix 2, in-place FFT. Bit reversed
addressing is corrected as the last step in the transform. No scaling is done.
Kiss uses a complex-only, time decimation, mixed-radix , out-of-place FFT.
No scaling is done.
LICENSE:
BSD, see COPYING for details. Basically, "free to use, give credit where due, no guarantees"
@ -76,7 +76,6 @@ LICENSE:
TODO:
*) Add sample code for parallel ffts (stereo) packed into re,im components of time sequence.
*) Add simple windowing function, e.g. Hamming : w(i)=.54-.46*cos(2pi*i/(n-1))
*) Could mixed-radix FFTs be made simple enough to stand by the KISS principle?
*) Make the fixed point scaling and bit shifts more easily configurable.
*) Document/revisit the input/output fft scaling
*) See if the fixed point code can be optimized a little without adding complexity.