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/* Example illustrating how to use mpfr_can_round. */
/*
Copyright 2016-2025 Free Software Foundation, Inc.
Contributed by the Pascaline 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/>.
*/
#include <stdio.h>
#include <mpfr.h>
int
main (void)
{
mpfr_t x, y;
mpfr_prec_t px = 53, py = 50;
mpfr_rnd_t r1, r2;
int ok;
/* Given an approximation of Pi to px bits computed with rounding mode r1,
we call mpfr_can_round() to see if we can deduced the correct rounding
of Pi to py bits with rounding mode r2.
The error is at most 1 = 2^0 ulp. This translates into err = prec(x). */
mpfr_init2 (x, px);
mpfr_init2 (y, py);
for (r1 = 0; r1 < 4; r1++)
{
mpfr_const_pi (x, r1);
printf ("r1=%s approx=", mpfr_print_rnd_mode (r1));
mpfr_out_str (stdout, 2, 0, x, MPFR_RNDN);
printf ("\n");
for (r2 = 0; r2 < 4; r2++)
{
ok = mpfr_can_round (x, mpfr_get_prec (x), r1, r2, py);
printf ("r2=%s ok=%d", mpfr_print_rnd_mode (r2), ok);
if (ok)
{
mpfr_set (y, x, r2);
printf (" ");
mpfr_out_str (stdout, 2, 0, y, MPFR_RNDN);
}
printf ("\n");
}
}
mpfr_clear (x);
mpfr_clear (y);
mpfr_free_cache ();
return 0;
}
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