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[Bug math/15416] New: catan, catanh inaccuracy from atan2
- From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Mon, 29 Apr 2013 16:25:54 +0000
- Subject: [Bug math/15416] New: catan, catanh inaccuracy from atan2
- Auto-submitted: auto-generated
http://sourceware.org/bugzilla/show_bug.cgi?id=15416
Bug #: 15416
Summary: catan, catanh inaccuracy from atan2
Product: glibc
Version: 2.17
Status: NEW
Severity: normal
Priority: P2
Component: math
AssignedTo: unassigned@sourceware.org
ReportedBy: jsm28@gcc.gnu.org
Classification: Unclassified
When catan computes __real__ res = 0.5 * __ieee754_atan2 (2.0 * __real__ x,
den), the value of den may be inaccurate when close to 0, resulting in an
inaccurate real part of the result when __real__ x is also small. For example,
catan (0x1p-27 + 1.0i) gives a result with real part 0.785398163397448279 on
x86_64, which is only accurate to 8 decimal places, about half the precision
expected (the exact value is 0.785398165260093458846617868453411006955...).
The same applies to catanh.
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