| 1 | /* Example illustrating how to use mpfr_can_round. */
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| 2 |
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| 3 | /*
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| 4 | Copyright 2016-2020 Free Software Foundation, Inc.
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| 5 | Contributed by the AriC and Caramba projects, INRIA.
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| 6 |
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| 7 | This file is part of the GNU MPFR Library.
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| 8 |
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| 9 | The GNU MPFR Library is free software; you can redistribute it and/or modify
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| 10 | it under the terms of the GNU Lesser General Public License as published by
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| 11 | the Free Software Foundation; either version 3 of the License, or (at your
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| 12 | option) any later version.
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| 13 |
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| 14 | The GNU MPFR Library is distributed in the hope that it will be useful, but
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| 15 | WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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| 16 | or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
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| 17 | License for more details.
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| 18 |
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| 19 | You should have received a copy of the GNU Lesser General Public License
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| 20 | along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
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| 21 | https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
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| 22 | 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
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| 23 | */
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| 24 |
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| 25 | #include <stdio.h>
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| 26 | #include <mpfr.h>
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| 27 |
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| 28 | int
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| 29 | main (void)
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| 30 | {
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| 31 | mpfr_t x, y;
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| 32 | mpfr_prec_t px = 53, py = 50;
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| 33 | mpfr_rnd_t r1, r2;
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| 34 | int ok;
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| 35 |
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| 36 | /* Given an approximation of Pi to px bits computed with rounding mode r1,
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| 37 | we call mpfr_can_round() to see if we can deduced the correct rounding
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| 38 | of Pi to py bits with rounding mode r2.
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| 39 | The error is at most 1 = 2^0 ulp. This translates into err = prec(x). */
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| 40 | mpfr_init2 (x, px);
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| 41 | mpfr_init2 (y, py);
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| 42 | for (r1 = 0; r1 < 4; r1++)
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| 43 | {
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| 44 | mpfr_const_pi (x, r1);
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| 45 | printf ("r1=%s approx=", mpfr_print_rnd_mode (r1));
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| 46 | mpfr_out_str (stdout, 2, 0, x, MPFR_RNDN);
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| 47 | printf ("\n");
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| 48 | for (r2 = 0; r2 < 4; r2++)
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| 49 | {
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| 50 | ok = mpfr_can_round (x, mpfr_get_prec (x), r1, r2, py);
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| 51 | printf ("r2=%s ok=%d", mpfr_print_rnd_mode (r2), ok);
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| 52 | if (ok)
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| 53 | {
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| 54 | mpfr_set (y, x, r2);
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| 55 | printf (" ");
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| 56 | mpfr_out_str (stdout, 2, 0, y, MPFR_RNDN);
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| 57 | }
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| 58 | printf ("\n");
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| 59 | }
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| 60 | }
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| 61 | mpfr_clear (x);
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| 62 | mpfr_clear (y);
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| 63 | mpfr_free_cache ();
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| 64 | return 0;
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| 65 | }
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