Re: factor_add_primes logic

[Jeroen Demeyer <jdemeyer@cage.ugent.be>]

Bill Allombert wrote:
> On Mon, Mar 23, 2009 at 11:59:36AM +0100, Jeroen Demeyer wrote:
> > 1) Continuing an interrupted (CTRL-C) factorization. Current behaviour  
> > works.
>
> > 2) Repeatedly doing the same factorization during a computation: say I  
> > need to compute znorder(Mod(a,n)) for several a's with n fixed and I am  
> > too lazy/stupid to give the factorization of n as an argument.  Also  
> > here, current behaviour works.
>
> > 3) Doing different factorizations but where the same prime factors occur  
> > multiple times.  Say P is a point on an elliptic curve and I want to  
> > factor the denominator of [n]P where n varies.  Here the current  
> > behaviour is not optimal, it would be better to add every large prime  
> > factor of the factorizations (even if the number-to-be-factored was 
> > prime).
>
> Why not call addprimes directly ?

Of course this can be done but then what is the point of 
factor_add_primes?  The current factor_add_primes supports
scenarios 1 and 2 that I wrote above but not 3.  Since it looks easy to 
also support scenario 3, I think it should be done.

Jeroen.