#11771: sage crashes on some degenerate flint xgcd's
--------------------------------+-------------------------------------------
Reporter: lftabera | Owner: AlexGhitza
Type: defect | Status: needs_review
Priority: critical | Milestone: sage-4.7.2
Component: basic arithmetic | Keywords: flint, crash, xgcd fmpq_poly
rational polynomials
Work_issues: | Upstream: N/A
Reviewer: | Author: Leif Leonhardy
Merged: | Dependencies:
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Comment(by spancratz):
I can confirm that the patch suggested by leif does the right thing. It
does have one extra re-allocation, though, which isn't necessary. I
suggest the following,
{{{
limbs = FLINT_MAX(fmpz_size(s->den), fmpz_size(t->den)) +
fmpz_size(rop->den);
temp = fmpz_init(limbs);
}}}
which might perhaps also be easier to read as it's two lines shorter?
Also, the two subsequent calls to fmpq_poly_canonicalize() should be
replaced by
{{{
fmpq_poly_canonicalize(s, NULL);
fmpq_poly_canonicalize(t, NULL);
}}}
If you look at the code for fmpq_poly_canonicalize() you'll see that this
is in fact not necessary at all since the function doesn't ever actually
use the temporary space passed in anyway. --- I realise this looks
rather bad. If you think this should be cleaned up on the occasion of
this ticket, let me know. ---
In any case, the above bit of code fixes this issue.
By the way, the tight re-use of fmpz variables in flint1 together with the
manual memory management is one of the biggest pains when working with
flint1. This is all much, much easier in flint2.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11771#comment:20>
Sage <http://www.sagemath.org>
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