1 /* mpfr_set_float128 -- convert a machine _Float128 number to
2 a multiple precision floating-point number
3
4 Copyright 2012-2023 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 #define MPFR_NEED_LONGLONG_H
25 #include "mpfr-impl.h"
26
27 #ifdef MPFR_WANT_FLOAT128
28
29 #if MPFR_WANT_FLOAT128 == 1
30 /* _Float128 type from ISO/IEC TS 18661 */
31 # define MPFR_FLOAT128_MAX 0x1.ffffffffffffffffffffffffffffp+16383f128
32 #elif MPFR_WANT_FLOAT128 == 2
33 /* __float128 type (GNU C extension) */
34 # define MPFR_FLOAT128_MAX 0x1.ffffffffffffffffffffffffffffp+16383q
35 #else
36 # error "Unsupported value for MPFR_WANT_FLOAT128"
37 #endif
38
39 int
40 mpfr_set_float128 (mpfr_ptr r, _Float128 d, mpfr_rnd_t rnd_mode)
41 {
42 mpfr_t t;
43 mp_limb_t *tp;
44 int inexact, shift_exp, neg, e, i;
45 _Float128 p[14], q[14];
46 MPFR_SAVE_EXPO_DECL (expo);
47
48 /* Check for NaN */
49 if (MPFR_UNLIKELY (DOUBLE_ISNAN (d)))
50 {
51 MPFR_SET_NAN(r);
52 MPFR_RET_NAN;
53 }
54
55 /* Check for INF */
56 if (MPFR_UNLIKELY (d > MPFR_FLOAT128_MAX))
57 {
58 MPFR_SET_INF (r);
59 MPFR_SET_POS (r);
60 return 0;
61 }
62 else if (MPFR_UNLIKELY (d < -MPFR_FLOAT128_MAX))
63 {
64 MPFR_SET_INF (r);
65 MPFR_SET_NEG (r);
66 return 0;
67 }
68 /* Check for ZERO */
69 else if (MPFR_UNLIKELY (d == (_Float128) 0.0))
70 return mpfr_set_d (r, (double) d, rnd_mode);
71
72 shift_exp = 0; /* invariant: remainder to deal with is d*2^shift_exp */
73 neg = d < 0;
74 if (d < 0)
75 d = -d;
76
77 /* Scaling, avoiding (slow) divisions. Should the tables be cached? */
78 if (d >= 1.0)
79 {
80 p[0] = 2.0;
81 q[0] = 0.5;
82 e = 1;
83 /* p[i] = 2^(2^i), q[i] = 1/p[i] */
84 for (i = 0; i < 13 && d >= p[i]; i++)
85 {
86 p[i+1] = p[i] * p[i];
87 q[i+1] = q[i] * q[i];
88 e <<= 1;
89 }
90 for (; i >= 0; e >>= 1, i--)
91 if (d >= p[i])
92 {
93 d *= q[i];
94 shift_exp += e;
95 }
96 d *= 0.5;
97 shift_exp++;
98 }
99 else if (d < 0.5)
100 {
101 p[0] = 2.0;
102 q[0] = 0.5;
103 e = 1;
104 /* p[i] = 2^(2^i), q[i] = 1/p[i] */
105 for (i = 0; i < 13 && d < q[i]; i++)
106 {
107 p[i+1] = p[i] * p[i];
108 q[i+1] = q[i] * q[i];
109 e <<= 1;
110 }
111 /* The while() may be needed for i = 13 due to subnormals.
112 This can probably be improved without yielding an underflow. */
113 for (; i >= 0; e >>= 1, i--)
114 while (d < q[i])
115 {
116 d *= p[i];
117 shift_exp -= e;
118 }
119 }
120
121 MPFR_ASSERTD (d >= 0.5 && d < 1.0);
122
123 mpfr_init2 (t, IEEE_FLOAT128_MANT_DIG);
124 tp = MPFR_MANT (t);
125
126 MPFR_SAVE_EXPO_MARK (expo);
127 MPFR_SET_EXP (t, shift_exp);
128 MPFR_SET_SIGN (t, neg ? MPFR_SIGN_NEG : MPFR_SIGN_POS);
129
130 for (i = MPFR_LAST_LIMB (t); i >= 0; i--)
131 {
132 d *= 2 * (_Float128) MPFR_LIMB_HIGHBIT;
133 tp[i] = (mp_limb_t) d;
134 d -= tp[i];
135 }
136
137 inexact = mpfr_set (r, t, rnd_mode);
138 mpfr_clear (t);
139
140 MPFR_SAVE_EXPO_FREE (expo);
141 return mpfr_check_range (r, inexact, rnd_mode);
142 }
143
144 #endif /* MPFR_WANT_FLOAT128 */