#10112: random_prime does not handle erroneous input gracefully - it hangs
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Reporter: drkirkby | Owner: was
Type: defect | Status: positive_review
Priority: major | Milestone: sage-4.8
Component: number theory | Keywords:
Work_issues: | Upstream: N/A
Reviewer: David Kirkby, Johan Bosman | Author: Mike Hansen,
Francis Clarke
Merged: | Dependencies:
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Changes (by johanbosman):
* status: needs_review => positive_review
* reviewer: David Kirkby => David Kirkby, Johan Bosman
Old description:
> As noted at #10111 and
>
> http://groups.google.com/group/sage-
> devel/browse_thread/thread/6e8d6f28c915830d?hl=en
>
> {{{random_prime()}}} is not well documented.
>
> But {{{random_prime()}}} is also broken for some erroneous input.
> Programs should always handle poor input properly, which is the case of
> Sage probably means generating an error message.
>
> {{{
> sage: random_prime(0,True,-1) # Hangs
> sage: random_prime(0,False,-1) # Hangs
> sage: random_prime(1,0,-23) # Hangs
> sage: random_prime(-12,0,-12) # Hangs
> sage: random_prime(0, proof=False, lbound=-12) # Hangs
> }}}
>
> Having a negative lower bound can cause the function to hang, but this is
> not always the case, as the example below shows. Here an error message is
> generated.
>
> {{{
> sage: random_prime(-12,0,-4)
> ---------------------------------------------------------------------------
> ValueError Traceback (most recent call
> last)
>
> /export/home/drkirkby/sage-4.6.alpha3/<ipython console> in <module>()
>
> /export/home/drkirkby/sage-4.6.alpha3/local/lib/python2.6/site-
> packages/sage/rings/arith.pyc in random_prime(n, proof, lbound)
> 1144 n = ZZ(n)
> 1145 if n < lbound:
> -> 1146 raise ValueError, "n must be greater than lbound:
> %s"%(lbound)
> 1147 elif n == 2:
> 1148 return ZZ(n)
>
> ValueError: n must be greater than lbound: -4
> }}}
>
> Dave
New description:
As noted at #10111 and
http://groups.google.com/group/sage-
devel/browse_thread/thread/6e8d6f28c915830d?hl=en
{{{random_prime()}}} is not well documented.
But {{{random_prime()}}} is also broken for some erroneous input. Programs
should always handle poor input properly, which is the case of Sage
probably means generating an error message.
{{{
sage: random_prime(0,True,-1) # Hangs
sage: random_prime(0,False,-1) # Hangs
sage: random_prime(1,0,-23) # Hangs
sage: random_prime(-12,0,-12) # Hangs
sage: random_prime(0, proof=False, lbound=-12) # Hangs
}}}
Having a negative lower bound can cause the function to hang, but this is
not always the case, as the example below shows. Here an error message is
generated.
{{{
sage: random_prime(-12,0,-4)
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
/export/home/drkirkby/sage-4.6.alpha3/<ipython console> in <module>()
/export/home/drkirkby/sage-4.6.alpha3/local/lib/python2.6/site-
packages/sage/rings/arith.pyc in random_prime(n, proof, lbound)
1144 n = ZZ(n)
1145 if n < lbound:
-> 1146 raise ValueError, "n must be greater than lbound:
%s"%(lbound)
1147 elif n == 2:
1148 return ZZ(n)
ValueError: n must be greater than lbound: -4
}}}
Dave
Apply
1. [attachment: trac_10112.patch]
1. [attachment: trac_10112-replacement-extra.patch]
to the Sage library.
--
Comment:
Replying to [comment:14 drkirkby]:
> Is there any reason this should not be changed to positive review if
the slowdown is very small?
>
I don't think so. The code looks okay, is well documented, and passes all
tests.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10112#comment:15>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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