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• From: Prathamesh Kulkarni <prathamesh dot kulkarni at linaro dot org>
• To: Tejas Joshi <tejasjoshi9673 at gmail dot com>
• Cc: GCC Development <gcc at gcc dot gnu dot org>
• Date: Mon, 4 Feb 2019 22:14:09 +0530
• References: <CACMrGjCeaZ7EoYqjLYiAJXjOtOfpJNo9zcbWhfarfkiLMN8YYA@mail.gmail.com> <CACMrGjCJ3r9+iNnFUOdajH+73HYHexv+mn7p_MHtn4jUn0d7-Q@mail.gmail.com> <ri6k1m9q6rm.fsf@suse.cz> <alpine.DEB.2.21.1810231631010.17157@digraph.polyomino.org.uk> <CACMrGjB6WLp0YS17b3prvbxvYnKtEsxhN3NOePN5SPVazNRM3A@mail.gmail.com> <alpine.DEB.2.21.1811161645480.12454@digraph.polyomino.org.uk> <CACMrGjC64UmP5-_hSiXyXrb2+cyqDqZ9iQMYJNn+mOKZ6G_LeQ@mail.gmail.com> <alpine.DEB.2.21.1901212257310.27116@digraph.polyomino.org.uk> <CACMrGjBw3-Xm1rHAanVUjYGC3SojJSgKZKL5B+HdkcTEOZ=Kkg@mail.gmail.com> <CACMrGjBBvv=taD6vCK9QcqQJYbGWJj_KSSeSBfnU_DRdcuonrw@mail.gmail.com> <alpine.DEB.2.21.1901231735280.25816@digraph.polyomino.org.uk> <CACMrGjC6NP5CE17M1gDf09B+2Gbufp3offHQmRX1D8hiWGrQ2Q@mail.gmail.com> <alpine.DEB.2.21.1901252130130.8264@digraph.polyomino.org.uk> <CACMrGjDxpwLcVGgAwTDN=LojT01dUTK03dCH54CR1wYFPjGjAg@mail.gmail.com> <CACMrGjARaj3Dy-PzSvTehLzchbDEdE8mbD0rH9Ko6Eu3mFERGg@mail.gmail.com> <CAAgBjMk+QBgY3YgMbuBaq--PkBWfN8jg42Fon1F6cbC2dRV2BA@mail.gmail.com> <CACMrGjC6Gk6UFr9T5iY0OgW5PJ92bB3tSrx59+D3FK+fMGYErQ@mail.gmail.com>

On Mon, 4 Feb 2019 at 21:27, Tejas Joshi <tejasjoshi9673@gmail.com> wrote:
>
> Thanks.
> > Did you add an entry for roundeven in builtins.def ?
> Yes, I did.
>
> Find here the attached patch.diff for which I did the changes to
> implement roundeven. There might be some unnecessary changes and some
> necessary changes which have not been made.
You haven't called roundeven() in the patch. You'll need to add an
entry in fold_const_call_ss()
similar to real_ceil, and probably in other places too.

Thanks,
Prathamesh
>
> Regards,
> -Tejas
>
> On Mon, 4 Feb 2019 at 20:36, Prathamesh Kulkarni
> <prathamesh.kulkarni@linaro.org> wrote:
> >
> > 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



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