[Bug c++/24479] New: GCC donot promote single precision correctly with optimization flag on

["dyang at mathworks dot com" <gcc-bugzilla at gcc dot gnu dot org>]

Please run the following code through gcc with -O3 flag, then run the
executable. The expected result is -13275031.0, but the result from the code is
-13275030.0. That is because the result from the addition (a+0.5) was stored in
a signle precision, not double precision as ISO C++ standard mandates. This is
causing numerical problems with our product. This bug might be associated with
other math built-in functions.


#include <math.h>
#include <stdio.h>


inline float foof(float a) {
    float b = floor(a + 0.5);
    return b;
}

int main(void) {
    float a = -13275031.0f;
    a = foof(a);
    printf("%f\n", a);
    return 0;
}


-- 
           Summary: GCC donot promote single precision correctly with
                    optimization flag on
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: dyang at mathworks dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24479