This is the mail archive of the glibc-bugs@sourceware.org mailing list for the glibc project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

[Bug math/15416] New: catan, catanh inaccuracy from atan2


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.

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]