#5624: matrices cache their hash, which causes subtle bugs when moving objects
between 32/64 bit
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Reporter: was | Owner: cwitty
Type: defect | Status: new
Priority: major | Milestone: sage-3.4.1
Component: misc | Keywords:
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{{{
On Sat, Mar 28, 2009 at 6:26 AM, Jason Bandlow <...> wrote:
>> I'm guessing this is a subtle 32 versus 64-bit issue involving
>> pickling and assumptions made somewhere in the combinat or other sage
>> code involving 32/64-bit. The notebook is 64-bit and I bet your
>> computer is 32-bit.
>>
>> By the way, this works on the notebook in the context of your session
above:
>>
>> for a, b in M.iteritems():
>> if a == key: print b
>>
>
> Thanks William! This does seem likely to be the problem. I'll do more
> investigation when I get a chance and see if I can find out precisely
> where the problem is.
I know of one place in sage where objects cache their hash for efficiency
reasons (e.g., I think Sage matrices do). I hadn't thought about the fact
that pickling, moving to an object to a platform where the hashes are
different, and unpickling, would result in the subtle issue above, but
that makes sense. Here is an example:
On a 32-bit platform do this:
sage: a = matrix(ZZ,2,[1,-2,4,1993938292]); a.set_immutable(); b = {a:5};
save(b,'/Users/wstein/b.sobj')
Then load b on a 64-bit platform (e.g. ,sage.math):
sage: a = matrix(ZZ,2,[1,-2,4,1993938292]); a.set_immutable(); b =
load('b.sobj'); b[a]
boom! KeyError ...
sage: sage: b.keys()[0] == a
True
The fix here is that right before pickling the cached hash of the matrix
should be deleted.
I don't know any other places in Sage that do the above.
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5624>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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