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[Bug math/18210] New: clog10 inaccuracy
- From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Tue, 07 Apr 2015 23:22:18 +0000
- Subject: [Bug math/18210] New: clog10 inaccuracy
- Auto-submitted: auto-generated
https://sourceware.org/bugzilla/show_bug.cgi?id=18210
Bug ID: 18210
Summary: clog10 inaccuracy
Product: glibc
Version: 2.21
Status: NEW
Severity: normal
Priority: P2
Component: math
Assignee: unassigned at sourceware dot org
Reporter: jsm28 at gcc dot gnu.org
clog10, using the dbl-64 version of atan2 in non-default rounding modes, can be
inaccurate beyond the 9ulp maximum considered acceptable by libm-test.inc. For
example, on x86_64:
Failure: Test: Imaginary part of: clog10_upward (0x1.f4755cp+0 - 0x4.29411p-4
i)
Result:
is: -5.74390044257056600618e-02 -0x1.d68a52b0be1890000000p-5
should be: -5.74390044257055767951e-02 -0x1.d68a52b0be17d0000000p-5
difference: 8.32667268468867405318e-17 0x1.80000000000000000000p-54
ulp : 12.0000
max.ulp : 5.0000
(I suspect there may in fact be cases where atan2 by itself is that inaccurate,
like atan in bug 18197, though I haven't yet found them in my random testing.)
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