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*From*: Tejas Joshi <tejasjoshi9673 at gmail dot com>*To*: gcc at gcc dot gnu dot org*Date*: Mon, 4 Feb 2019 20:13:18 +0530*Subject*: Re: About GSOC.*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>

Hello. I have implemented roundeven function in real.c as follows: (and respective changes in real.h) /* 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? 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

**Follow-Ups**:**Re: About GSOC.***From:*Prathamesh Kulkarni

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