[Bug c/50773] float values are printed with greater precision than the float data type has when given as an argument to printf()

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50773

--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-10-18 14:49:28 UTC ---
On Tue, 18 Oct 2011, rguenth at gcc dot gnu.org wrote:

> Needs -fexcess-precision=standard -m32 to trigger.  libcpp does the
> parsing of FP constants IIRC, and the C++ frontend does not implement
> -fexcess-precision.
> 
> CCing Joseph.
> 
> Testcase that fails with -fexcess-precision=standard -m32:
> 
> extern void abort (void);
> int
> main()
> {
>       float a = 268517138.f;
>       if (a != 268517138.f)
>         abort ();
>       return 0;
> }

I don't see any bug there.  With -fexcess-precision=standard, 
FLT_EVAL_METHOD is 2, "evaluate all operations and constants to the range 
and precision of the long double type".  Thus 268517138.f has type float 
but a value represented to the precision of long double - and the 
conversion to the precision of float takes place for the initialization 
but not for the comparison.  (Without -fexcess-precision=standard - 
outside any conformance mode - FLT_EVAL_METHOD is still 2, but exactly 
what happens is unpredictable.)