1/* Test of the double rounding effect. 2 * 3 * This example was presented at the CNC'2 summer school on MPFR and MPC 4 * at LORIA, Nancy, France. 5 * 6 * Arguments: max difference of exponents dmax, significand size n. 7 * Optional argument: extended precision p (with double rounding). 8 * 9 * Return all the couples of positive machine numbers (x,y) such that 10 * 1/2 <= y < 1, 0 <= Ex - Ey <= dmax, x - y is exactly representable 11 * in precision n and the results of floor(x/y) in the rounding modes 12 * toward 0 and to nearest are different. 13 */ 14 15/* 16Copyright 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc. 17Contributed by the AriC and Caramel projects, INRIA. 18 19This file is part of the GNU MPFR Library. 20 21The GNU MPFR Library is free software; you can redistribute it and/or modify 22it under the terms of the GNU Lesser General Public License as published by 23the Free Software Foundation; either version 3 of the License, or (at your 24option) any later version. 25 26The GNU MPFR Library is distributed in the hope that it will be useful, but 27WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 28or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 29License for more details. 30 31You should have received a copy of the GNU Lesser General Public License 32along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 33http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 3451 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. 35*/ 36 37#include <stdio.h> 38#include <stdlib.h> 39#include <mpfr.h> 40 41#define PRECN x, y, z 42#define VARS PRECN, t 43 44static unsigned long 45eval (mpfr_t x, mpfr_t y, mpfr_t z, mpfr_t t, mpfr_rnd_t rnd) 46{ 47 mpfr_div (t, x, y, rnd); /* the division x/y in precision p */ 48 mpfr_set (z, t, rnd); /* the rounding to the precision n */ 49 mpfr_rint_floor (z, z, rnd); 50 return mpfr_get_ui (z, rnd); 51} 52 53int main (int argc, char *argv[]) 54{ 55 int dmax, n, p; 56 mpfr_t VARS; 57 58 if (argc != 3 && argc != 4) 59 { 60 fprintf (stderr, "Usage: divworst <dmax> <n> [ <p> ]\n"); 61 exit (EXIT_FAILURE); 62 } 63 64 dmax = atoi (argv[1]); 65 n = atoi (argv[2]); 66 p = argc == 3 ? n : atoi (argv[3]); 67 if (p < n) 68 { 69 fprintf (stderr, "divworst: p must be greater or equal to n\n"); 70 exit (EXIT_FAILURE); 71 } 72 73 mpfr_inits2 (n, PRECN, (mpfr_ptr) 0); 74 mpfr_init2 (t, p); 75 76 for (mpfr_set_ui_2exp (x, 1, -1, MPFR_RNDN); 77 mpfr_get_exp (x) <= dmax; 78 mpfr_nextabove (x)) 79 for (mpfr_set_ui_2exp (y, 1, -1, MPFR_RNDN); 80 mpfr_get_exp (y) == 0; 81 mpfr_nextabove (y)) 82 { 83 unsigned long rz, rn; 84 85 if (mpfr_sub (z, x, y, MPFR_RNDZ) != 0) 86 continue; /* x - y is not representable in precision n */ 87 rz = eval (x, y, z, t, MPFR_RNDZ); 88 rn = eval (x, y, z, t, MPFR_RNDN); 89 if (rz == rn) 90 continue; 91 mpfr_printf ("x = %.*Rb ; y = %.*Rb ; Z: %lu ; N: %lu\n", 92 n - 1, x, n - 1, y, rz, rn); 93 } 94 95 mpfr_clears (VARS, (mpfr_ptr) 0); 96 return 0; 97} 98