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 <math.h>
24 #include <math_private.h>
25 #include <stdlib.h>
26
27 /* Convert a `long double' in IEEE854 quad-precision format to a
28 multi-precision integer representing the significand scaled up by its
29 number of bits (113 for long double) and an integral power of two
30 (MPN frexpl). */
31
32 mp_size_t
33 __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size,
34 int *expt, int *is_neg,
35 _Float128 value)
36 {
37 union ieee854_long_double u;
38 u.d = value;
39
40 *is_neg = u.ieee.negative;
41 *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS;
42
43 #if BITS_PER_MP_LIMB == 32
44 res_ptr[0] = u.ieee.mantissa3; /* Low-order 32 bits of fraction. */
45 res_ptr[1] = u.ieee.mantissa2;
46 res_ptr[2] = u.ieee.mantissa1;
47 res_ptr[3] = u.ieee.mantissa0; /* High-order 32 bits. */
48 #define N 4
49 #elif BITS_PER_MP_LIMB == 64
50 /* Hopefully the compiler will combine the two bitfield extracts
51 and this composition into just the original quadword extract. */
52 res_ptr[0] = ((mp_limb_t) u.ieee.mantissa2 << 32) | u.ieee.mantissa3;
53 res_ptr[1] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
54 #define N 2
55 #else
56 #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
57 #endif
58 /* The format does not fill the last limb. There are some zeros. */
59 #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
60 - (LDBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
61
62 if (u.ieee.exponent == 0)
63 {
64 /* A biased exponent of zero is a special case.
65 Either it is a zero or it is a denormal number. */
66 if (res_ptr[0] == 0 && res_ptr[1] == 0
67 && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4. */
68 /* It's zero. */
69 *expt = 0;
70 else
71 {
72 /* It is a denormal number, meaning it has no implicit leading
73 one bit, and its exponent is in fact the format minimum. */
74 int cnt;
75
76 #if N == 2
77 if (res_ptr[N - 1] != 0)
78 {
79 count_leading_zeros (cnt, res_ptr[N - 1]);
80 cnt -= NUM_LEADING_ZEROS;
81 res_ptr[N - 1] = res_ptr[N - 1] << cnt
82 | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
83 res_ptr[0] <<= cnt;
84 *expt = LDBL_MIN_EXP - 1 - cnt;
85 }
86 else
87 {
88 count_leading_zeros (cnt, res_ptr[0]);
89 if (cnt >= NUM_LEADING_ZEROS)
90 {
91 res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
92 res_ptr[0] = 0;
93 }
94 else
95 {
96 res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
97 res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
98 }
99 *expt = LDBL_MIN_EXP - 1
100 - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
101 }
102 #else
103 int j, k, l;
104
105 for (j = N - 1; j > 0; j--)
106 if (res_ptr[j] != 0)
107 break;
108
109 count_leading_zeros (cnt, res_ptr[j]);
110 cnt -= NUM_LEADING_ZEROS;
111 l = N - 1 - j;
112 if (cnt < 0)
113 {
114 cnt += BITS_PER_MP_LIMB;
115 l--;
116 }
117 if (!cnt)
118 for (k = N - 1; k >= l; k--)
119 res_ptr[k] = res_ptr[k-l];
120 else
121 {
122 for (k = N - 1; k > l; k--)
123 res_ptr[k] = res_ptr[k-l] << cnt
124 | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt);
125 res_ptr[k--] = res_ptr[0] << cnt;
126 }
127
128 for (; k >= 0; k--)
129 res_ptr[k] = 0;
130 *expt = LDBL_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt;
131 #endif
132 }
133 }
134 else
135 /* Add the implicit leading one bit for a normalized number. */
136 res_ptr[N - 1] |= (mp_limb_t) 1 << (LDBL_MANT_DIG - 1
137 - ((N - 1) * BITS_PER_MP_LIMB));
138
139 return N;
140 }