20080905, 15:47  #1 
Mar 2007
Austria
456_{8} Posts 
Questions on coding my FFT&LLR implementation
I know that there is a fftthread in this forum, but it's still to hard for me. I'm currently coding an implementation of the LLR(Lucaslehmerriesel) test.It's currently using the GMP and I want to implement FFT for it. Can you please explain me the way from the x^2 calculation(I think that's the point where FFT helps) to the FFT. Also,if possible,can you show me an example on a small mersenne number(LL test)? This might help me a lot in understanding.
Thanks, nuggetprime 
20080905, 18:02  #2 
∂^{2}ω=0
Sep 2002
República de California
2D3C_{16} Posts 
Search for the thread titled "FFT explanation for non math guys".
Last fiddled with by ewmayer on 20080905 at 18:02 
20080905, 23:29  #3 
"Richard B. Woods"
Aug 2002
Wisconsin USA
7692_{10} Posts 
... in the Math subforum. Start at its post #5.

20080905, 23:58  #4 
P90 years forever!
Aug 2002
Yeehaw, FL
2·7·521 Posts 

20080906, 10:03  #5 
Mar 2007
Austria
2×151 Posts 
Thanks,I'm now understanding DFT in basics.
How does then the IBDWT work(different)? There aren't many resources on the web to this. Thanks, nugget 
20080906, 13:29  #6 
P90 years forever!
Aug 2002
Yeehaw, FL
1110001111110_{2} Posts 

20080907, 14:08  #7 
Mar 2007
Austria
2·151 Posts 
Question: What's the best way to store the transformed numbers? floating point,or?
Thanks, nuggetprime 
20080908, 17:41  #8 
Mar 2007
Austria
2×151 Posts 
Otherwise formulated:is double enough for,say, FFT length 500K?
Thanks, nuggetprime 
20080909, 14:01  #9 
Tribal Bullet
Oct 2004
110111001110_{2} Posts 
Yes, double precision should be plenty. It may be just insufficient if you are not careful with how you generate the trig factors for the FFT; references often use a recursion for them which causes increased roundoff error for very long transform lengths.

20080910, 15:19  #10 
Mar 2007
Austria
2×151 Posts 
Thank you for your answer jasonp.
But how can I calculate in binary in C? I probably will have to create arrays of 1bit fields,or? Thanks, nugget 
20080910, 17:32  #11 
Mar 2007
Austria
2×151 Posts 
The above was not stated precisely, I think.
I want to know if in C, when i define a ,say, unsigned short int, how can I access a certain bit of it,in reasonable CPU time? Thanks, nuggetprime Last fiddled with by nuggetprime on 20080910 at 17:33 
Thread Tools  
Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Anyone know enough about coding to do this?  jrafanelli  Software  2  20180111 15:16 
Python Coding Help?  kelzo  Programming  3  20161127 05:16 
Zhang's OPQBT coding help?  flouran  Programming  0  20090725 02:43 
coding midlet for TF  starrynte  Programming  1  20081230 22:31 
Coding Challenges  R.D. Silverman  Programming  18  20050809 13:14 