[Bug c++/40186] New: floating point comparision works wrong ( !(a < b) && (b > a) is true )

["ich at az2000 dot de" <gcc-bugzilla@gcc.gnu.org>]

When comparing the return value of two functions (which both return double and
do always return the same value), I have the case that (a < b) && (b < a)
(whereby they should be equal) in a real world application.

I tried to reproduce it, though in the test case, I have a slightly different
case, which should be also wrong: !(a < b) && (b > a) is true (whereby it
should be a == b).

Probably both problems are related.

The behaviour pretty much depend on the optimisation. With -O0 and -Os, I am
hitting the problem, but not so with -O1, -O2 and -O3.


-- 
           Summary: floating point comparision works wrong ( !(a < b) && (b
                    > a) is true )
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: ich at az2000 dot de
 GCC build triplet: tried with GCC 4.1.2, 4.3.2 and 4.4.0
  GCC host triplet: Gentoo Linux i386
GCC target triplet: Linux i386


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40186