Fix ginac's ratlog method so log(int(0),2) does not hang #39135
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Documentation preview for this PR (built with commit f9a3b43; changes) is ready! 🎉 |
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Technically this makes the comment of the method incorrect (?) it says an infinity is not a MPZ/MPQ. But then there's also a |
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Good point. I think it makes sense to just add "(or an infinity)" at the end. How does that sound? |
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Sounds good. |
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sagemathgh-39135: Fix ginac's ratlog method so log(int(0),2) does not hang Fixes sagemath#37794. It is explained in sagemath#37794 that calculating the logarithm of `int(0)` (zero represented as a python integer) can enter an infinite loop, due to a bug in ginac's `numeric::ratlog` method. This PR adds an `if` statement to return negative infinity for this value. (At this point in the code, the base of the logarithm is known to be a positive integer that is greater than 1, so the log of 0 is negative infinity, not positive infinity.) The PR also adds `log(int(0), 2)` as a doctest and, for good measure, also `log(int(0), 1/2)`. ### 📝 Checklist <!-- Put an `x` in all the boxes that apply. --> - [x] The title is concise and informative. - [x] The description explains in detail what this PR is about. - [x] I have linked a relevant issue or discussion. - [x] I have created tests covering the changes. - [x] I have updated the documentation and checked the documentation preview. ### ⌛ Dependencies <!-- List all open PRs that this PR logically depends on. For example, --> <!-- - sagemath#12345: short description why this is a dependency --> <!-- - sagemath#34567: ... --> URL: sagemath#39135 Reported by: DaveWitteMorris Reviewer(s): Lorenz Panny
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Fixes #37794.
It is explained in #37794 that calculating the logarithm of
int(0)(zero represented as a python integer) can enter an infinite loop, due to a bug in ginac'snumeric::ratlogmethod. This PR adds anifstatement to return negative infinity for this value. (At this point in the code, the base of the logarithm is known to be a positive integer that is greater than 1, so the log of 0 is negative infinity, not positive infinity.)The PR also adds
log(int(0), 2)as a doctest and, for good measure, alsolog(int(0), 1/2).📝 Checklist
⌛ Dependencies