[Bug math/14994] New: casinh, casin inaccuracy from cancellation

["jsm28 at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14994

             Bug #: 14994
           Summary: casinh, casin inaccuracy from cancellation
           Product: glibc
           Version: 2.16
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: jsm28@gcc.gnu.org
    Classification: Unclassified


casinh is inaccurate for large arguments with negative real part because it
uses the formula clog (z + csqrt (1 + z*z)), and for such arguments the square
root is approximately -z, rather than approximately z, so there is loss of
precision from cancellation in the addition.  For example, on x86_64 casinh
(-1.0 + 0x1p500i) returns -inf + 0i rather than the expected -347.266... +
1.57079...i.

casin has similar problems since it's implemented in terms of casinh.

-- 
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.