This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC 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]

Re: About GSOC.


On Mon, 4 Feb 2019 at 20:10, Tejas Joshi <tejasjoshi9673@gmail.com> wrote:
>
> Hello.
> I have implemented roundeven function in real.c as follows: (and
> respective changes in real.h)
It's a better idea to include all changes in patch instead of copy-pasting.
Use the command:
git diff > patch.diff
which will create a file called "patch.diff" containing the changes
and send it as an attachment.
>
> /* Round X to nearest even integer towards zero. */
>
> void
> real_roundeven (REAL_VALUE_TYPE *r, format_helper fmt,
>         const REAL_VALUE_TYPE *x)
> {
>   REAL_VALUE_TYPE t;
>
>   do_fix_trunc (&t, x);
>   HOST_WIDE_INT i = real_to_integer (&t);
>   if(i % 2)
>     do_add (r, &t, &dconstm1, 0);
>   else
>     *r = t;
> }
>
> Although I cant get it to test like
>
> int foo()
> {
>     double x = __builtin_roundeven (3.5);
>     printf("%f",x);
>     return (int) x;
> }
> Because I do not know its dependencies through other files. I tried to
> track them down by inspecting real_ceil function, but it also includes
> other optimization procedures like folding. How do I know enough
> declarations to be made in respective files?
Did you add an entry for roundeven in builtins.def ?

Thanks,
Prathamesh
>
> Thanks.
> -Tejas
>
> On Mon, 28 Jan 2019 at 22:33, Tejas Joshi <tejasjoshi9673@gmail.com> wrote:
> >
> > Hello.
> > Representations of real numbers in real.c are a little complex to
> > understand right now for me. I am still trying to understand them and
> > figure them out using gdb and cscope. Though conventions are given in
> > comments in real.c, I will still be trying to figure it out. The
> > equation and its bitwise representation is not pretty elaborated in
> > any documentation I could find.
> >
> > x = s * b^e * \sum_{k=1}^p f_k * b^{-k}
> >
> >     where
> >         s = sign (+- 1)
> >         b = base or radix, here always 2
> >         e = exponent
> >         p = precision (the number of base-b digits in the significand)
> >         f_k = the digits of the significand.
> >
> > In mean time, I've tried real_round function to work like roundeven. I
> > will try to submit a clean patch along with roundeven implemented
> > separately with changes like in builtins.def, adding cases, etc.
> >
> > void
> > real_round (REAL_VALUE_TYPE *r, format_helper fmt,
> >         const REAL_VALUE_TYPE *x)
> > {
> > #if 0
> >   do_add (r, x, &dconsthalf, x->sign);
> >   do_fix_trunc (r, r);
> >   if (fmt)
> >     real_convert (r, fmt, r);
> > #endif
> >   fprintf (stderr, "\nhere\n");
> >   real_value z;
> >   do_fix_trunc (&z, x);
> >   HOST_WIDE_INT i = real_to_integer (&z);
> >   fprintf (stderr, "\n i = %ld\n", i);
> >   if (i % 2)
> >     do_add (r, &z, &dconstm1, 0);
> >   else
> >     *r = z;
> > }
> >
> > Thanks.
> > -Tejas
> >
> > On Sat, 26 Jan 2019 at 03:02, Joseph Myers <joseph@codesourcery.com> wrote:
> > >
> > > On Sat, 26 Jan 2019, Tejas Joshi wrote:
> > >
> > > > function with byte-byte comparison which also include mpfr. (Correct
> > > > me if I am wrong.) What is the significance of mpfr related to these
> > > > internal representations?
> > >
> > > real.c provides a fixed-size representation of floating-point numbers that
> > > allows for various non-IEEE formats supported by GCC, and also allows
> > > functions from dfp.c to be used for decimal floating-point formats.
> > >
> > > MPFR is used in GCC to provide operations that are nontrivial to
> > > implement, especially those that are nontrivial to implement in such a
> > > fixed-size context.  real.c operations wrap around MPFR ones where
> > > appropriate, doing whatever's needed in cases where there are non-IEEE
> > > semantics or sets of values.
> > >
> > > --
> > > Joseph S. Myers
> > > joseph@codesourcery.com


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]