1 | /* Copyright (C) 1995-2022 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 <stdlib.h> |
25 | |
26 | /* Convert a `long double' in IEEE854 standard double-precision format to a |
27 | multi-precision integer representing the significand scaled up by its |
28 | number of bits (64 for long double) and an integral power of two |
29 | (MPN frexpl). */ |
30 | |
31 | mp_size_t |
32 | (mp_ptr res_ptr, mp_size_t size, |
33 | int *expt, int *is_neg, |
34 | long double value) |
35 | { |
36 | union ieee854_long_double u; |
37 | u.d = value; |
38 | |
39 | *is_neg = u.ieee.negative; |
40 | *expt = (int) u.ieee.exponent - IEEE854_LONG_DOUBLE_BIAS; |
41 | |
42 | #if BITS_PER_MP_LIMB == 32 |
43 | res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction. */ |
44 | res_ptr[1] = u.ieee.mantissa0; /* High-order 32 bits. */ |
45 | #define N 2 |
46 | #elif BITS_PER_MP_LIMB == 64 |
47 | /* Hopefully the compiler will combine the two bitfield extracts |
48 | and this composition into just the original quadword extract. */ |
49 | res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1; |
50 | #define N 1 |
51 | #else |
52 | #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for" |
53 | #endif |
54 | |
55 | if (u.ieee.exponent == 0) |
56 | { |
57 | /* A biased exponent of zero is a special case. |
58 | Either it is a zero or it is a denormal number. */ |
59 | if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2. */ |
60 | /* It's zero. */ |
61 | *expt = 0; |
62 | else |
63 | { |
64 | /* It is a denormal number, meaning it has no implicit leading |
65 | one bit, and its exponent is in fact the format minimum. */ |
66 | int cnt; |
67 | |
68 | if (res_ptr[N - 1] != 0) |
69 | { |
70 | count_leading_zeros (cnt, res_ptr[N - 1]); |
71 | if (cnt != 0) |
72 | { |
73 | #if N == 2 |
74 | res_ptr[N - 1] = res_ptr[N - 1] << cnt |
75 | | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt)); |
76 | res_ptr[0] <<= cnt; |
77 | #else |
78 | res_ptr[N - 1] <<= cnt; |
79 | #endif |
80 | } |
81 | *expt = LDBL_MIN_EXP - 1 - cnt; |
82 | } |
83 | else |
84 | { |
85 | count_leading_zeros (cnt, res_ptr[0]); |
86 | res_ptr[N - 1] = res_ptr[0] << cnt; |
87 | res_ptr[0] = 0; |
88 | *expt = LDBL_MIN_EXP - 1 - BITS_PER_MP_LIMB - cnt; |
89 | } |
90 | } |
91 | } |
92 | |
93 | return N; |
94 | } |
95 | |