#14817: Inefficiency in copying PARI objects to the heap
-------------------------------+--------------------------------------------
Reporter: pbruin | Owner: tbd
Type: enhancement | Status: needs_review
Priority: minor | Milestone: sage-5.12
Component: performance | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Peter Bruin | Merged in:
Dependencies: | Stopgaps:
-------------------------------+--------------------------------------------
Changes (by pbruin):
* status: new => needs_review
Old description:
> When PARI objects are wrapped into Python objects, they are copied from
> the PARI stack to a `malloc`'ed memory block. This is done by the
> function `deepcopy_to_python_heap()` in `sage/libs/pari/gen.pyx`. To
> determine how much memory to allocate, this function creates a dummy copy
> on the stack and measures by how much the stack pointer goes down. This
> is inefficient and can be improved by calling PARI's `gsizebyte()`
> function, which does exactly what we want.
>
> Also, copying the object to the `malloc`'ed block is done inelegantly by
> temporarily changing the global variables `top`, `bot` and `avma`
> defining the PARI stack. Again, there is a PARI function that does what
> we want: `gcopy_avma()` does the same as `gcopy()`, but copies to a user-
> specified address.
>
> I am attaching a patch that replaces `deepcopy_to_python_heap()` by a
> simpler and faster implementation. (It also deletes a comment that seems
> to refer to code that no longer exists.)
New description:
When PARI objects are wrapped into Python objects, they are copied from
the PARI stack to a `malloc`'ed memory block. This is done by the
function `deepcopy_to_python_heap()` in `sage/libs/pari/gen.pyx`. To
determine how much memory to allocate, this function creates a dummy copy
on the stack and measures by how much the stack pointer goes down. This
is inefficient and can be improved by calling PARI's `gsizebyte()`
function, which does exactly what we want.
Also, copying the object to the `malloc`'ed block is done inelegantly by
temporarily changing the global variables `top`, `bot` and `avma` defining
the PARI stack. Again, there is a PARI function that does what we want:
`gcopy_avma()` does the same as `gcopy()`, but copies to a user-specified
address.
I am attaching a patch that replaces `deepcopy_to_python_heap()` by a
simpler and faster implementation. (It also deletes a comment that seems
to refer to code that no longer exists.)
Apply: [attachment:trac14817-copy_pari_objects.patch]
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/14817#comment:1>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/groups/opt_out.
