[Bug libfortran/48906] Wrong rounding results with -m32

["thenlich at users dot sourceforge.net" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48906

--- Comment #35 from Thomas Henlich <thenlich at users dot sourceforge.net> 2011-06-10 16:56:02 UTC ---
(In reply to comment #33)
> The last test case I am working is fmt_g0_6.f08. 
> 
> The apparent failing case is:
> 
>       print "(rc,g15.2)", 0.995000_8
> 
> Which is resulting in 0.99 and we expect it to be 1.0.
> 
> However, the raw internal representation of 0.995 is not exact and is:
> 
> 99499999999999999555
> 
> This places the value less then the threshold given in the table in the
> Standard, giving the correct F format as:
> 
>       print "(f11.2,4x)", 0.995000_8  ! 0.99
> 
> Instead of 
> 
>       print "(f11.1,4x)", 0.995000_8  ! 1.0
> 
> 
> Our F formatting in the test case is using the f11.1 and the logic does not
> look at the third digit and dutifully rounds the value as it should.  The new G
> formatting is using exact integer logic and dutifully does look at the third
> digit.
> 
> If we do:
> 
> print "(rc,g15.2)", 0.9950001_8
> 
> The internal value does cross the 0.995 threshold and we do get the 1.0
> results.
> 
> I think this issues is one of those splitting hairs things.  We could
> artificially round the digits string early before we process it, but this would
> effectively be rounding twice to get there.  I would prefer to revise the test
> case like so:
> 
>   call check_all(0.995000000001_RT, 15, 2, 0)
> 
> and be done with this.

The result is correct, but our expectation was wrong.

0.995000_8 which is internally 0.99499999999999999555... is smaller than 0.995
(exact value) so it must output 0.99, not 1.0.

Please don't waste time with this test case (fmt_g0_6.f08), it is broken. I
will fix this some time.