consolidate shifts in polynomial_template

[robertwb]

See discussion at end of #4965.

CC: @malb @burcin

Component: algebra

Author: Alex Ghitza, Martin Albrecht

Reviewer: Alex Ghitza, Martin Albrecht

Merged: sage-4.3.alpha1

Issue created by migration from https://trac.sagemath.org/ticket/4982

[sagetrac-mabshoff]

comment:2

3.4 is for ReST tickets only.

Cheers,

Michael

[aghitza]

comment:3

The point was to consolidate the three shift methods shift, __lshift__, and __rshift__ by having shift do all the work and the other two call it. (Right now there's significant code triplication going on.)

The attached patch does this.

[aghitza]

Author: Alex Ghitza

[aghitza]

comment:4

Attachment: trac_4982.patch.gz

I'm ccing the participants in the discussion at #4965 in case they had something else in mind.

[malb]

comment:5

The only issue I can see is the potential performance overhead.

Vanilla 4.2.1:

sage: P.<x> = GF(2)[]
sage: f = P.random_element(50)
sage: %timeit f<<50
1000000 loops, best of 3: 792 ns per loop

This patch:

sage: P.<x> = GF(2)[]
sage: f = P.random_element(50)
sage: %timeit f<<50
1000000 loops, best of 3: 952 ns per loop

Maybe a cdef method could be added which everyone (shift, __lshift__, __rshift__) calls?

[malb]

comment:6

Doctests pass btw., applies cleanly etc.