1 /* Example illustrating how to use mpfr_can_round. */ 2 3 /* 4 Copyright 2016-2023 Free Software Foundation, Inc. 5 Contributed by the AriC and Caramba projects, INRIA. 6 7 This file is part of the GNU MPFR Library. 8 9 The GNU MPFR Library is free software; you can redistribute it and/or modify 10 it under the terms of the GNU Lesser General Public License as published by 11 the Free Software Foundation; either version 3 of the License, or (at your 12 option) any later version. 13 14 The GNU MPFR Library is distributed in the hope that it will be useful, but 15 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 16 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 17 License for more details. 18 19 You should have received a copy of the GNU Lesser General Public License 20 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 21 https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 22 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. 23 */ 24 25 #include <stdio.h> 26 #include <mpfr.h> 27 28 int 29 main (void) 30 { 31 mpfr_t x, y; 32 mpfr_prec_t px = 53, py = 50; 33 mpfr_rnd_t r1, r2; 34 int ok; 35 36 /* Given an approximation of Pi to px bits computed with rounding mode r1, 37 we call mpfr_can_round() to see if we can deduced the correct rounding 38 of Pi to py bits with rounding mode r2. 39 The error is at most 1 = 2^0 ulp. This translates into err = prec(x). */ 40 mpfr_init2 (x, px); 41 mpfr_init2 (y, py); 42 for (r1 = 0; r1 < 4; r1++) 43 { 44 mpfr_const_pi (x, r1); 45 printf ("r1=%s approx=", mpfr_print_rnd_mode (r1)); 46 mpfr_out_str (stdout, 2, 0, x, MPFR_RNDN); 47 printf ("\n"); 48 for (r2 = 0; r2 < 4; r2++) 49 { 50 ok = mpfr_can_round (x, mpfr_get_prec (x), r1, r2, py); 51 printf ("r2=%s ok=%d", mpfr_print_rnd_mode (r2), ok); 52 if (ok) 53 { 54 mpfr_set (y, x, r2); 55 printf (" "); 56 mpfr_out_str (stdout, 2, 0, y, MPFR_RNDN); 57 } 58 printf ("\n"); 59 } 60 } 61 mpfr_clear (x); 62 mpfr_clear (y); 63 mpfr_free_cache (); 64 return 0; 65 } 66