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
31mp_size_t
32__mpn_extract_long_double (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

source code of glibc/sysdeps/ieee754/ldbl-96/ldbl2mpn.c