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/14785] New: Incorrect results from fma in round-toward-zero mode when a * b is small and of opposite sign to c


http://sourceware.org/bugzilla/show_bug.cgi?id=14785

             Bug #: 14785
           Summary: Incorrect results from fma in round-toward-zero mode
                    when a * b is small and of opposite sign to c
           Product: glibc
           Version: 2.16
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: jsm28@gcc.gnu.org
    Classification: Unclassified


fma (a, b, c) gives incorrect results in round-to-zero mode in some cases when
a * b is sufficiently small that the implementation uses a * b + c for the
computation, but a * b has opposite sign to c.  Example, on x86: fmal
(0x1p-16382L, -0x1p-16382L, 0x1p16383L).  In such a case, a * b rounds to zero,
and so the final result returned is equal to c, but correct rounding towards
zero should return the next value after c in the direction of 0.  Using a * b +
c would give the correct results in the other three rounding modes, but not in
FE_TOWARDZERO mode when the signs differ like this.

-- 
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]