99 lines
3.0 KiB
C
99 lines
3.0 KiB
C
/* Test of the double rounding effect.
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*
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* This example was presented at the CNC'2 summer school on MPFR and MPC
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* at LORIA, Nancy, France.
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*
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* Arguments: max difference of exponents dmax, significand size n.
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* Optional argument: extended precision p (with double rounding).
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*
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* Return all the couples of positive machine numbers (x,y) such that
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* 1/2 <= y < 1, 0 <= Ex - Ey <= dmax, x - y is exactly representable
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* in precision n and the results of floor(x/y) in the rounding modes
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* toward 0 and to nearest are different.
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*/
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/*
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Copyright 2009-2022 Free Software Foundation, Inc.
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Contributed by the AriC and Caramba projects, INRIA.
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This file is part of the GNU MPFR Library.
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The GNU MPFR Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 3 of the License, or (at your
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option) any later version.
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The GNU MPFR Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
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https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
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51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <mpfr.h>
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#define PRECN x, y, z
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#define VARS PRECN, t
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static unsigned long
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eval (mpfr_t x, mpfr_t y, mpfr_t z, mpfr_t t, mpfr_rnd_t rnd)
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{
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mpfr_div (t, x, y, rnd); /* the division x/y in precision p */
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mpfr_set (z, t, rnd); /* the rounding to the precision n */
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mpfr_rint_floor (z, z, rnd);
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return mpfr_get_ui (z, rnd);
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}
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int main (int argc, char *argv[])
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{
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int dmax, n, p;
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mpfr_t VARS;
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if (argc != 3 && argc != 4)
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{
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fprintf (stderr, "Usage: divworst <dmax> <n> [ <p> ]\n");
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exit (EXIT_FAILURE);
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}
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dmax = atoi (argv[1]);
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n = atoi (argv[2]);
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p = argc == 3 ? n : atoi (argv[3]);
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if (p < n)
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{
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fprintf (stderr, "divworst: p must be greater or equal to n\n");
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exit (EXIT_FAILURE);
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}
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mpfr_inits2 (n, PRECN, (mpfr_ptr) 0);
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mpfr_init2 (t, p);
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for (mpfr_set_ui_2exp (x, 1, -1, MPFR_RNDN);
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mpfr_get_exp (x) <= dmax;
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mpfr_nextabove (x))
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for (mpfr_set_ui_2exp (y, 1, -1, MPFR_RNDN);
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mpfr_get_exp (y) == 0;
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mpfr_nextabove (y))
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{
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unsigned long rz, rn;
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if (mpfr_sub (z, x, y, MPFR_RNDZ) != 0)
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continue; /* x - y is not representable in precision n */
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rz = eval (x, y, z, t, MPFR_RNDZ);
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rn = eval (x, y, z, t, MPFR_RNDN);
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if (rz == rn)
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continue;
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mpfr_printf ("x = %.*Rb ; y = %.*Rb ; Z: %lu ; N: %lu\n",
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n - 1, x, n - 1, y, rz, rn);
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}
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mpfr_clears (VARS, (mpfr_ptr) 0);
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mpfr_free_cache ();
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return 0;
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}
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