1 /* Copyright (C) 1995-2023 Free Software Foundation, Inc.
2 This file is part of the GNU C Library.
3
4 The GNU C Library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 The GNU C Library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with the GNU C Library; if not, see
16 <https://www.gnu.org/licenses/>. */
17
18 #include "gmp.h"
19 #include "gmp-impl.h"
20 #include "longlong.h"
21 #include <ieee754.h>
22 #include <float.h>
23 #include <stdlib.h>
24
25 /* Convert a `long double' in IEEE854 standard double-precision format to a
26 multi-precision integer representing the significand scaled up by its
27 number of bits (64 for long double) and an integral power of two
28 (MPN frexpl). */
29
30 mp_size_t
31 __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size,
32 int *expt, int *is_neg,
33 long double value)
34 {
35 union ieee854_long_double u;
36 u.d = value;
37
38 *is_neg = u.ieee.negative;
39 *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;
40
41 #if BITS_PER_MP_LIMB == 32
42 res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction. */
43 res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits. */
44 #define N 2
45 #elif BITS_PER_MP_LIMB == 64
46 /* Hopefully the compiler will combine the two bitfield extracts
47 and this composition into just the original quadword extract. */
48 res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
49 #define N 1
50 #else
51 #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
52 #endif
53
54 if (u.ieee.exponent == 0)
55 {
56 /* A biased exponent of zero is a special case.
57 Either it is a zero or it is a denormal number. */
58 if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2. */
59 /* It's zero. */
60 *expt = 0;
61 else
62 {
63 /* It is a denormal number, meaning it has no implicit leading
64 one bit, and its exponent is in fact the format minimum. */
65 int cnt;
66
67 /* One problem with Intel's 80-bit format is that the explicit
68 leading one in the normalized representation has to be zero
69 for denormalized number. If it is one, the number is according
70 to Intel's specification an invalid number. We make the
71 representation unique by explicitly clearing this bit. */
72 res_ptr[N - 1] &= ~((mp_limb_t) 1 << ((LDBL_MANT_DIG - 1) % BITS_PER_MP_LIMB));
73
74 if (res_ptr[N - 1] != 0)
75 {
76 count_leading_zeros (cnt, res_ptr[N - 1]);
77 if (cnt != 0)
78 {
79 #if N == 2
80 res_ptr[N - 1] = res_ptr[N - 1] << cnt
81 | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
82 res_ptr[0] <<= cnt;
83 #else
84 res_ptr[N - 1] <<= cnt;
85 #endif
86 }
87 *expt = LDBL_MIN_EXP - 1 - cnt;
88 }
89 else if (res_ptr[0] != 0)
90 {
91 count_leading_zeros (cnt, res_ptr[0]);
92 res_ptr[N - 1] = res_ptr[0] << cnt;
93 res_ptr[0] = 0;
94 *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt;
95 }
96 else
97 {
98 /* This is the special case of the pseudo denormal number
99 with only the implicit leading bit set. The value is
100 in fact a normal number and so we have to treat this
101 case differently. */
102 #if N == 2
103 res_ptr[N - 1] = 0x80000000ul;
104 #else
105 res_ptr[0] = 0x8000000000000000ul;
106 #endif
107 *expt = LDBL_MIN_EXP - 1;
108 }
109 }
110 }
111 else if (u.ieee.exponent < 0x7fff
112 #if N == 2
113 && res_ptr[0] == 0
114 #endif
115 && res_ptr[N - 1] == 0)
116 /* Pseudo zero. */
117 *expt = 0;
118
119 return N;
120 }