get_d.c revision 1.1.1.3
1/* mpfr_get_d, mpfr_get_d_2exp -- convert a multiple precision floating-point 2 number to a machine double precision float 3 4Copyright 1999-2018 Free Software Foundation, Inc. 5Contributed by the AriC and Caramba projects, INRIA. 6 7This file is part of the GNU MPFR Library. 8 9The GNU MPFR Library is free software; you can redistribute it and/or modify 10it under the terms of the GNU Lesser General Public License as published by 11the Free Software Foundation; either version 3 of the License, or (at your 12option) any later version. 13 14The GNU MPFR Library is distributed in the hope that it will be useful, but 15WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 16or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 17License for more details. 18 19You should have received a copy of the GNU Lesser General Public License 20along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see 21http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc., 2251 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */ 23 24#include <float.h> 25 26#define MPFR_NEED_LONGLONG_H 27#include "mpfr-impl.h" 28 29#include "ieee_floats.h" 30 31/* Assumes IEEE-754 double precision; otherwise, only an approximated 32 result will be returned, without any guaranty (and special cases 33 such as NaN must be avoided if not supported). */ 34 35double 36mpfr_get_d (mpfr_srcptr src, mpfr_rnd_t rnd_mode) 37{ 38 double d; 39 int negative; 40 mpfr_exp_t e; 41 42 if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (src))) 43 { 44 if (MPFR_IS_NAN (src)) 45 return MPFR_DBL_NAN; 46 47 negative = MPFR_IS_NEG (src); 48 49 if (MPFR_IS_INF (src)) 50 return negative ? MPFR_DBL_INFM : MPFR_DBL_INFP; 51 52 MPFR_ASSERTD (MPFR_IS_ZERO(src)); 53 return negative ? DBL_NEG_ZERO : 0.0; 54 } 55 56 e = MPFR_GET_EXP (src); 57 negative = MPFR_IS_NEG (src); 58 59 if (MPFR_UNLIKELY(rnd_mode == MPFR_RNDA)) 60 rnd_mode = negative ? MPFR_RNDD : MPFR_RNDU; 61 62 /* the smallest normalized number is 2^(-1022)=0.1e-1021, and the smallest 63 subnormal is 2^(-1074)=0.1e-1073 */ 64 if (MPFR_UNLIKELY (e < -1073)) 65 { 66 /* Note: Avoid using a constant expression DBL_MIN * DBL_EPSILON 67 as this gives 0 instead of the correct result with gcc on some 68 Alpha machines. */ 69 d = negative ? 70 (rnd_mode == MPFR_RNDD || 71 (rnd_mode == MPFR_RNDN && mpfr_cmp_si_2exp(src, -1, -1075) < 0) 72 ? -DBL_MIN : DBL_NEG_ZERO) : 73 (rnd_mode == MPFR_RNDU || 74 (rnd_mode == MPFR_RNDN && mpfr_cmp_si_2exp(src, 1, -1075) > 0) 75 ? DBL_MIN : 0.0); 76 if (d != 0.0) /* we multiply DBL_MIN = 2^(-1022) by DBL_EPSILON = 2^(-52) 77 to get +-2^(-1074) */ 78 d *= DBL_EPSILON; 79 } 80 /* the largest normalized number is 2^1024*(1-2^(-53))=0.111...111e1024 */ 81 else if (MPFR_UNLIKELY (e > 1024)) 82 { 83 d = negative ? 84 (rnd_mode == MPFR_RNDZ || rnd_mode == MPFR_RNDU ? 85 -DBL_MAX : MPFR_DBL_INFM) : 86 (rnd_mode == MPFR_RNDZ || rnd_mode == MPFR_RNDD ? 87 DBL_MAX : MPFR_DBL_INFP); 88 } 89 else 90 { 91 int nbits; 92 mp_size_t np, i; 93 mp_limb_t tp[ MPFR_LIMBS_PER_DOUBLE ]; 94 int carry; 95 96 nbits = IEEE_DBL_MANT_DIG; /* 53 */ 97 if (MPFR_UNLIKELY (e < -1021)) 98 /*In the subnormal case, compute the exact number of significant bits*/ 99 { 100 nbits += (1021 + e); 101 MPFR_ASSERTD (nbits >= 1); 102 } 103 np = MPFR_PREC2LIMBS (nbits); 104 MPFR_ASSERTD ( np <= MPFR_LIMBS_PER_DOUBLE ); 105 carry = mpfr_round_raw_4 (tp, MPFR_MANT(src), MPFR_PREC(src), negative, 106 nbits, rnd_mode); 107 if (MPFR_UNLIKELY(carry)) 108 d = 1.0; 109 else 110 { 111 /* The following computations are exact thanks to the previous 112 mpfr_round_raw. */ 113 d = (double) tp[0] / MP_BASE_AS_DOUBLE; 114 for (i = 1 ; i < np ; i++) 115 d = (d + tp[i]) / MP_BASE_AS_DOUBLE; 116 /* d is the mantissa (between 1/2 and 1) of the argument rounded 117 to 53 bits */ 118 } 119 d = mpfr_scale2 (d, e); 120 if (negative) 121 d = -d; 122 } 123 124 return d; 125} 126 127#undef mpfr_get_d1 128double 129mpfr_get_d1 (mpfr_srcptr src) 130{ 131 return mpfr_get_d (src, __gmpfr_default_rounding_mode); 132} 133 134double 135mpfr_get_d_2exp (long *expptr, mpfr_srcptr src, mpfr_rnd_t rnd_mode) 136{ 137 double ret; 138 mpfr_exp_t exp; 139 mpfr_t tmp; 140 141 if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (src))) 142 { 143 int negative; 144 *expptr = 0; 145 if (MPFR_IS_NAN (src)) 146 return MPFR_DBL_NAN; 147 negative = MPFR_IS_NEG (src); 148 if (MPFR_IS_INF (src)) 149 return negative ? MPFR_DBL_INFM : MPFR_DBL_INFP; 150 MPFR_ASSERTD (MPFR_IS_ZERO(src)); 151 return negative ? DBL_NEG_ZERO : 0.0; 152 } 153 154 MPFR_ALIAS (tmp, src, MPFR_SIGN (src), 0); 155 ret = mpfr_get_d (tmp, rnd_mode); 156 157 if (MPFR_IS_PURE_FP(src)) 158 { 159 exp = MPFR_GET_EXP (src); 160 161 /* rounding can give 1.0, adjust back to 0.5 <= abs(ret) < 1.0 */ 162 if (ret == 1.0) 163 { 164 ret = 0.5; 165 exp++; 166 } 167 else if (ret == -1.0) 168 { 169 ret = -0.5; 170 exp++; 171 } 172 173 MPFR_ASSERTN ((ret >= 0.5 && ret < 1.0) 174 || (ret <= -0.5 && ret > -1.0)); 175 MPFR_ASSERTN (exp >= LONG_MIN && exp <= LONG_MAX); 176 } 177 else 178 exp = 0; 179 180 *expptr = exp; 181 return ret; 182} 183