Multiplication action by -2^63 hangs

[jdemeyer]

sage: E = EllipticCurve(GF(5),[0,1])
sage: P = E.random_element()
sage: (-2^63)*P   # hangs

Component: coercion

Author: Jeroen Demeyer

Branch/Commit: 1c074bb

Reviewer: Vincent Delecroix

Issue created by migration from https://trac.sagemath.org/ticket/17844

[jdemeyer]

Branch: u/jdemeyer/ticket/17844

[jdemeyer]

Commit: b5402b0

[jdemeyer]

New commits:

b5402b0

Fix IntegerMulAction by -2^63, check for interrupts

[videlec]

comment:3

Cleaner and faster option in fast_mul_long that avoid coercions

- return parent_c(a)(0)
+ try:
+     return parent_c(a).zero()
+ except AttributeError:
+     return parent_c(a)(0)

Related note: It would be much better if this code for multiplication was closer to generic_power_c in sage.structure.element. And by the way, it would be cool to have a generic_power_long_c.

Vincent

[videlec]

comment:4

The change is not only important but needed! And it would be cool to have a comment saying why, i.e. -LONG_MIN = LONG_MIN for longs.

Vincent

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

1c074bb

Small improvement to IntegerMulAction by 0

[sagetrac-git]

Changed commit from b5402b0 to 1c074bb

[videlec]

Reviewer: Vincent Delecroix

[videlec]

comment:7

The improvement for the 0 case is not an improvement for elliptic curves since the group does not implement the method zero... but this is a different story.

Good to me!

[vbraun]

Changed branch from u/jdemeyer/ticket/17844 to 1c074bb