1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
|
/* mpfr_get_d, mpfr_get_d_2exp -- convert a multiple precision floating-point
number to a machine double precision float
Copyright 1999-2021 Free Software Foundation, Inc.
Contributed by the AriC and Caramba projects, INRIA.
This file is part of the GNU MPFR Library.
The GNU MPFR Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 3 of the License, or (at your
option) any later version.
The GNU MPFR Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
https://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
#include <float.h>
#define MPFR_NEED_LONGLONG_H
#include "mpfr-impl.h"
#include "ieee_floats.h"
/* Assumes IEEE-754 double precision; otherwise, only an approximated
result will be returned, without any guaranty (and special cases
such as NaN must be avoided if not supported). */
double
mpfr_get_d (mpfr_srcptr src, mpfr_rnd_t rnd_mode)
{
double d;
int negative;
mpfr_exp_t e;
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (src)))
{
if (MPFR_IS_NAN (src))
{
/* we don't propagate the sign bit */
return MPFR_DBL_NAN;
}
negative = MPFR_IS_NEG (src);
if (MPFR_IS_INF (src))
return negative ? MPFR_DBL_INFM : MPFR_DBL_INFP;
MPFR_ASSERTD (MPFR_IS_ZERO(src));
return negative ? DBL_NEG_ZERO : 0.0;
}
e = MPFR_GET_EXP (src);
negative = MPFR_IS_NEG (src);
if (MPFR_UNLIKELY(rnd_mode == MPFR_RNDA))
rnd_mode = negative ? MPFR_RNDD : MPFR_RNDU;
/* the smallest normalized number is 2^(-1022)=0.1e-1021, and the smallest
subnormal is 2^(-1074)=0.1e-1073 */
if (MPFR_UNLIKELY (e < -1073))
{
/* Note: Avoid using a constant expression DBL_MIN * DBL_EPSILON
as this gives 0 instead of the correct result with gcc on some
Alpha machines. */
d = negative ?
(rnd_mode == MPFR_RNDD ||
(rnd_mode == MPFR_RNDN && mpfr_cmp_si_2exp(src, -1, -1075) < 0)
? -DBL_MIN : DBL_NEG_ZERO) :
(rnd_mode == MPFR_RNDU ||
(rnd_mode == MPFR_RNDN && mpfr_cmp_si_2exp(src, 1, -1075) > 0)
? DBL_MIN : 0.0);
if (d != 0.0) /* we multiply DBL_MIN = 2^(-1022) by DBL_EPSILON = 2^(-52)
to get +-2^(-1074) */
d *= DBL_EPSILON;
}
/* the largest normalized number is 2^1024*(1-2^(-53))=0.111...111e1024 */
else if (MPFR_UNLIKELY (e > 1024))
{
d = negative ?
(rnd_mode == MPFR_RNDZ || rnd_mode == MPFR_RNDU ?
-DBL_MAX : MPFR_DBL_INFM) :
(rnd_mode == MPFR_RNDZ || rnd_mode == MPFR_RNDD ?
DBL_MAX : MPFR_DBL_INFP);
}
else
{
int nbits;
mp_limb_t tp[ MPFR_LIMBS_PER_DOUBLE ];
int carry;
nbits = IEEE_DBL_MANT_DIG; /* 53 */
if (MPFR_UNLIKELY (e < -1021))
/*In the subnormal case, compute the exact number of significant bits*/
{
nbits += 1021 + e;
MPFR_ASSERTD (1 <= nbits && nbits < IEEE_DBL_MANT_DIG);
}
carry = mpfr_round_raw_4 (tp, MPFR_MANT(src), MPFR_PREC(src), negative,
nbits, rnd_mode);
if (MPFR_UNLIKELY(carry))
d = 1.0;
else
{
#if MPFR_LIMBS_PER_DOUBLE == 1
d = (double) tp[0] / MP_BASE_AS_DOUBLE;
#else
mp_size_t np, i;
MPFR_ASSERTD (nbits <= IEEE_DBL_MANT_DIG);
np = MPFR_PREC2LIMBS (nbits);
MPFR_ASSERTD ( np <= MPFR_LIMBS_PER_DOUBLE );
/* The following computations are exact thanks to the previous
mpfr_round_raw. */
d = (double) tp[0] / MP_BASE_AS_DOUBLE;
for (i = 1 ; i < np ; i++)
d = (d + tp[i]) / MP_BASE_AS_DOUBLE;
/* d is the mantissa (between 1/2 and 1) of the argument rounded
to 53 bits */
#endif
}
d = mpfr_scale2 (d, e);
if (negative)
d = -d;
}
return d;
}
#undef mpfr_get_d1
double
mpfr_get_d1 (mpfr_srcptr src)
{
return mpfr_get_d (src, __gmpfr_default_rounding_mode);
}
double
mpfr_get_d_2exp (long *expptr, mpfr_srcptr src, mpfr_rnd_t rnd_mode)
{
double ret;
mpfr_exp_t exp;
mpfr_t tmp;
if (MPFR_UNLIKELY (MPFR_IS_SINGULAR (src)))
{
int negative;
*expptr = 0;
if (MPFR_IS_NAN (src))
{
/* we don't propagate the sign bit */
return MPFR_DBL_NAN;
}
negative = MPFR_IS_NEG (src);
if (MPFR_IS_INF (src))
return negative ? MPFR_DBL_INFM : MPFR_DBL_INFP;
MPFR_ASSERTD (MPFR_IS_ZERO(src));
return negative ? DBL_NEG_ZERO : 0.0;
}
MPFR_ALIAS (tmp, src, MPFR_SIGN (src), 0);
ret = mpfr_get_d (tmp, rnd_mode);
exp = MPFR_GET_EXP (src);
/* rounding can give 1.0, adjust back to 0.5 <= abs(ret) < 1.0 */
if (ret == 1.0)
{
ret = 0.5;
exp++;
}
else if (ret == -1.0)
{
ret = -0.5;
exp++;
}
MPFR_ASSERTN ((ret >= 0.5 && ret < 1.0)
|| (ret <= -0.5 && ret > -1.0));
MPFR_ASSERTN (exp >= LONG_MIN && exp <= LONG_MAX);
*expptr = exp;
return ret;
}
|
