From 445b21561953743e869197605a44ad809ec570bb Mon Sep 17 00:00:00 2001 From: Mark Borgerding Date: Thu, 27 Oct 2005 20:10:54 +0000 Subject: [PATCH] *** empty log message *** --- README | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/README b/README index 131f9f9..e3b6267 100644 --- a/README +++ b/README @@ -60,7 +60,7 @@ 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. - 4. FFT_BRANDX is roughly twice as fast as KISS FFT. + 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 @@ -68,6 +68,16 @@ 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. + + Q: Why don't I get the output I expect? + A: The two most common causes of this are + 1) scaling : is there a constant mutliplier between what you got and what you want? + 2) mixed build environment -- all code must be compiled with same preprocessor + definitions for DATATYPE & FIXED_POINT + PERFORMANCE: (on Athlon XP 2100+, with gcc 2.96, float data type) @@ -83,7 +93,11 @@ DO NOT: UNDER THE HOOD: Kiss FFT uses a time decimation, mixed-radix, out-of-place FFT. -No scaling is done. Optimized butterflies are used for factors 2,3,4, and 5. + + No scaling is done for the floating point version (for speed). + Scaling is done both ways for the fixed-point version (for overflow prevention). + + Optimized butterflies are used for factors 2,3,4, and 5. The real optimization code only works for even length ffts. It does two half-length FFTs in parallel (packed into real&imag), and then combines them via twiddling. @@ -92,15 +106,15 @@ No scaling is done. Optimized butterflies are used for factors 2,3,4, and 5. modified to put the scrap at the tail. LICENSE: - BSD, see COPYING for details. Basically, "free to use&change, give credit where due, no guarantees" + Revised BSD License, see COPYING 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 TODO: *) Add real optimization for odd length FFTs (DST?) *) Add real optimization to the n-dimensional FFT - *) Add simple windowing function, e.g. Hamming : w(i)=.54-.46*cos(2pi*i/(n-1)) - *) 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. *) 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)