Mersenne: FFT modulo a prime

[Naessens Yan]

I have just subscribed to this mailing-list even if I am very interested in 
both programming and primes search.
I intend to write a program to find prime Mersenne numbers using 
Lucas-Lehmer test and FFT in Z/mZ (the ring of integers modulo an prime 
integer m). The language I use for this purpose is Caml-Light, but I also 
know C and Pascal languages.
I represent big numbers with arrays. I choose m=7*2^26+1. Thus, I have 26 
free bits per element of arrays, so I decide to represent my big numbers in 
binary using the 26 first bits of each elements of arrays.
I have a problem with the multiplication (the square). When I do the IFFT, 
to get back 'the coefficients of the polynom' that represents the number I 
have to square, I may get a 'coefficient' between 2^26 and 7*2^26+1 since 
all operations are modulo m.
What do I have to do with the 26th,27th and 28th bits ?
P.S.:I have already read the FAQ ; I just want to make a FFT to multiply 
numbers without taking the result mod a Mersenne number.

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Mersenne: Re: Another mprime is running

[Wojciech Florek]

Hi
I have observed similar effects using my PC. But I know
the reason. My Linux hasn't been instaleld properly...
I don't want to reinstall it so I'm working with such unpleasent behavior.
How is it working?

1. Usually I start mprime in using local.ini or, if stopped during a
   session, from the text terminal.
2. On the other hand, I mainly work using X11 (gnome version).
3. When I shuttdown sustem using GUI sometimes it happens that
   X11 is closed (but mprime has been started from the text interface),
   so mprime is still running.
4. Instead of stopping  (runlevel 0, if I remember well) the system
   reboots in the text mode, so rclocal.ini is again procceeded.
   Then, among others, mprime is started onece more and the message
   "Another mprime is running" appears. It doesn't hurt, so I do
   nothing with it till the system (or/and hardware) upgrade.
   
So, in my case, it isn't error in the mprime but in my system.
Regards and happy hunting!

Wojtek Florek
==
Wojciech Florek (WsF)
Adam Mickiewicz University, Institute of Physics
ul. Umultowska 85, 61-614 Poznan, Poland

phone: (++48-61) 8273033 fax: (++48-61) 8257758
email: [EMAIL PROTECTED] 


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