1/* mpfr_sub -- subtract two floating-point numbers 2 3Copyright 2001, 2002, 2003, 2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Free Software Foundation, Inc. 4Contributed by the AriC and Caramel projects, INRIA. 5 6This file is part of the GNU MPFR Library. 7 8The GNU MPFR Library is free software; you can redistribute it and/or modify 9it under the terms of the GNU Lesser General Public License as published by 10the Free Software Foundation; either version 3 of the License, or (at your 11option) any later version. 12 13The GNU MPFR Library is distributed in the hope that it will be useful, but 14WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 15or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 16License for more details. 17 18You should have received a copy of the GNU Lesser General Public License 19along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 20http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 2151 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 22 23#include "mpfr-impl.h" 24 25int 26mpfr_sub (mpfr_ptr a, mpfr_srcptr b, mpfr_srcptr c, mpfr_rnd_t rnd_mode) 27{ 28 MPFR_LOG_FUNC 29 (("b[%Pu]=%.*Rg c[%Pu]=%.*Rg rnd=%d", 30 mpfr_get_prec (b), mpfr_log_prec, b, 31 mpfr_get_prec (c), mpfr_log_prec, c, rnd_mode), 32 ("a[%Pu]=%.*Rg", mpfr_get_prec (a), mpfr_log_prec, a)); 33 34 if (MPFR_ARE_SINGULAR (b,c)) 35 { 36 if (MPFR_IS_NAN (b) || MPFR_IS_NAN (c)) 37 { 38 MPFR_SET_NAN (a); 39 MPFR_RET_NAN; 40 } 41 else if (MPFR_IS_INF (b)) 42 { 43 if (!MPFR_IS_INF (c) || MPFR_SIGN (b) != MPFR_SIGN(c)) 44 { 45 MPFR_SET_INF (a); 46 MPFR_SET_SAME_SIGN (a, b); 47 MPFR_RET (0); /* exact */ 48 } 49 else 50 { 51 MPFR_SET_NAN (a); /* Inf - Inf */ 52 MPFR_RET_NAN; 53 } 54 } 55 else if (MPFR_IS_INF (c)) 56 { 57 MPFR_SET_INF (a); 58 MPFR_SET_OPPOSITE_SIGN (a, c); 59 MPFR_RET (0); /* exact */ 60 } 61 else if (MPFR_IS_ZERO (b)) 62 { 63 if (MPFR_IS_ZERO (c)) 64 { 65 int sign = rnd_mode != MPFR_RNDD 66 ? ((MPFR_IS_NEG(b) && MPFR_IS_POS(c)) ? -1 : 1) 67 : ((MPFR_IS_POS(b) && MPFR_IS_NEG(c)) ? 1 : -1); 68 MPFR_SET_SIGN (a, sign); 69 MPFR_SET_ZERO (a); 70 MPFR_RET(0); /* 0 - 0 is exact */ 71 } 72 else 73 return mpfr_neg (a, c, rnd_mode); 74 } 75 else 76 { 77 MPFR_ASSERTD (MPFR_IS_ZERO (c)); 78 return mpfr_set (a, b, rnd_mode); 79 } 80 } 81 82 MPFR_ASSERTD (MPFR_IS_PURE_FP (b)); 83 MPFR_ASSERTD (MPFR_IS_PURE_FP (c)); 84 85 if (MPFR_LIKELY (MPFR_SIGN (b) == MPFR_SIGN (c))) 86 { /* signs are equal, it's a real subtraction */ 87 if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b) 88 && MPFR_PREC (b) == MPFR_PREC (c))) 89 return mpfr_sub1sp (a, b, c, rnd_mode); 90 else 91 return mpfr_sub1 (a, b, c, rnd_mode); 92 } 93 else 94 { /* signs differ, it's an addition */ 95 if (MPFR_GET_EXP (b) < MPFR_GET_EXP (c)) 96 { /* exchange rounding modes toward +/- infinity */ 97 int inexact; 98 rnd_mode = MPFR_INVERT_RND (rnd_mode); 99 if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b) 100 && MPFR_PREC (b) == MPFR_PREC (c))) 101 inexact = mpfr_add1sp (a, c, b, rnd_mode); 102 else 103 inexact = mpfr_add1 (a, c, b, rnd_mode); 104 MPFR_CHANGE_SIGN (a); 105 return -inexact; 106 } 107 else 108 { 109 if (MPFR_LIKELY (MPFR_PREC (a) == MPFR_PREC (b) 110 && MPFR_PREC (b) == MPFR_PREC (c))) 111 return mpfr_add1sp (a, b, c, rnd_mode); 112 else 113 return mpfr_add1 (a, b, c, rnd_mode); 114 } 115 } 116} 117