#15337: Speed up ulp() method of real_mpfr.pyx
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Reporter: jdemeyer | Owner:
Type: enhancement | Status: needs_work
Priority: minor | Milestone: sage-5.13
Component: basic arithmetic | Resolution:
Keywords: | Merged in:
Authors: Jeroen Demeyer | Reviewers:
Report Upstream: N/A | Work issues: documentation
Branch: | Commit:
Dependencies: | Stopgaps:
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Changes (by jdemeyer):
* work_issues: segfault in fp_rank, error in nextabove => documentation
Comment:
Replying to [comment:11 zimmerma]:
> "Adding or subtracting something less than half an ulp always gives the
same number (unless the number is exactly a power of 2...)": the case of
the opposite of a power of 2 is missing here, also this assumes the
rounding mode is to nearest.
Fair enough, this documentation should be fixed.
> I don't see the logic of returning {{{self}}} for NaN but not for
infinities.
So what do you prefer: never returning `self`? returning `self` for `NaN`
and `+Inf` but not for `-Inf`?
> Since the patch also adds tests for {{{fp_rank}}} (which I discovered)
That's an indepedent bug deserving a new ticket: #15363.
> If {{{a}}} is the smallest positive non-zero number, then the next
number should be {{{2*a}}}.
In MPFR, this isn't true since MPFR doesn't have denormal numbers.
--
Ticket URL: <http://trac.sagemath.org/ticket/15337#comment:12>
Sage <http://www.sagemath.org>
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