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/* Test of the double rounding effect.
*
* This example was presented at the CNC'2 summer school on MPFR and MPC
* at LORIA, Nancy, France.
*
* Arguments: max difference of exponents dmax, significand size n.
* Optional argument: extended precision p (with double rounding).
*
* Return all the couples of positive machine numbers (x,y) such that
* 1/2 <= y < 1, 0 <= Ex - Ey <= dmax, x - y is exactly representable
* in precision n and the results of floor(x/y) in the rounding modes
* toward 0 and to nearest are different.
*/
/*
Copyright 2009-2021 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.
The GNU MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <stdio.h>
#include <stdlib.h>
#include <mpfr.h>
#define PRECN x, y, z
#define VARS PRECN, t
static unsigned long
eval (mpfr_t x, mpfr_t y, mpfr_t z, mpfr_t t, mpfr_rnd_t rnd)
{
mpfr_div (t, x, y, rnd); /* the division x/y in precision p */
mpfr_set (z, t, rnd); /* the rounding to the precision n */
mpfr_rint_floor (z, z, rnd);
return mpfr_get_ui (z, rnd);
}
int main (int argc, char *argv[])
{
int dmax, n, p;
mpfr_t VARS;
if (argc != 3 && argc != 4)
{
fprintf (stderr, "Usage: divworst <dmax> <n> [ <p> ]\n");
exit (EXIT_FAILURE);
}
dmax = atoi (argv[1]);
n = atoi (argv[2]);
p = argc == 3 ? n : atoi (argv[3]);
if (p < n)
{
fprintf (stderr, "divworst: p must be greater or equal to n\n");
exit (EXIT_FAILURE);
}
mpfr_inits2 (n, PRECN, (mpfr_ptr) 0);
mpfr_init2 (t, p);
for (mpfr_set_ui_2exp (x, 1, -1, MPFR_RNDN);
mpfr_get_exp (x) <= dmax;
mpfr_nextabove (x))
for (mpfr_set_ui_2exp (y, 1, -1, MPFR_RNDN);
mpfr_get_exp (y) == 0;
mpfr_nextabove (y))
{
unsigned long rz, rn;
if (mpfr_sub (z, x, y, MPFR_RNDZ) != 0)
continue; /* x - y is not representable in precision n */
rz = eval (x, y, z, t, MPFR_RNDZ);
rn = eval (x, y, z, t, MPFR_RNDN);
if (rz == rn)
continue;
mpfr_printf ("x = %.*Rb ; y = %.*Rb ; Z: %lu ; N: %lu\n",
n - 1, x, n - 1, y, rz, rn);
}
mpfr_clears (VARS, (mpfr_ptr) 0);
mpfr_free_cache ();
return 0;
}
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