Karim BELABAS on Mon, 8 Sep 2003 13:57:58 +0200 (MEST) |
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Re: nfeltpowmodpr segfault on degree-1 ideals |
On Mon, 8 Sep 2003, Bill Allombert wrote: > Dear PARI dev > > It seems that nfeltpowmodpr SEGV on degree 1 ideal: > ? K=nfinit(x^2+1);pr=nfmodprinit(K,idealprimedec(K,5)[1]); > ? nfeltpowmodpr(K,x,2,pr); > *** bug in GP (Segmentation Fault), please report > > For some reason to_ff_init return NULL for the polynomial, > but FpXQ_pow will not handle it. All FpXQxxx(..., T,p) routines [ computations with lifted elements of Fp[X]/(T) ] were supposed to handle the case of prime fields [ T = NULL ]. For some reason, this one did not... Fixed. Karim. P.S: the nf*modpr routines are obsolete and simple GP wrappers around more useful library routines, retained for backward compatibility since there's no GP interface to work efficiently in finite fields. Basically, it's a waste to work in O_K / pr [ "dimension n" ], rather than directly in the isomorphic finite field [ "dimension f(pr/p) ]. nf_to_ff / ff_to_nf provide the required conversions routines, which should only be used once [ the wrappers use them in the obvious way... ] P.S2: there was some problems with the precise specifications of the "modular" routines, e.g * are t_INT allowed as representants for elements in polynomial quotient rings (currently "often". Fqxxx routines should be used instead but...). * does omitting an argument (p = NULL or T = NULL) corresponds to cancelling the reduction (mod p or mod T), or does T = NULL correspond to the more specific case of a prime field. The latter is more useful since one can suppress the reduction mod p to work in char. 0 quotient rings R[X] / (T), whereas there's no reason to use a FpXQ routine and to suppress reduction mod T. Since the routines are not yet documented, it would be a good idea to decide once and for all. -- Karim Belabas Tel: (+33) (0)1 69 15 57 48 Dép. de Mathématiques, Bât. 425 Fax: (+33) (0)1 69 15 60 19 Université Paris-Sud http://www.math.u-psud.fr/~belabas/ F-91405 Orsay (France) http://www.parigp-home.de/ [PARI/GP]