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688903eb | 1 | /* Copyright (C) 1995-2018 Free Software Foundation, Inc. |
f964490f RM |
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 | |
59ba27a6 PE |
15 | License along with the GNU C Library; if not, see |
16 | <http://www.gnu.org/licenses/>. */ | |
f964490f RM |
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 IBM extended format to a multi-precision | |
27 | integer representing the significand scaled up by its number of | |
28 | bits (106 for long double) and an integral power of two (MPN | |
29 | frexpl). */ | |
30 | ||
37a4c70b PM |
31 | |
32 | /* When signs differ, the actual value is the difference between the | |
33 | significant double and the less significant double. Sometimes a | |
34 | bit can be lost when we borrow from the significant mantissa. */ | |
35 | #define EXTRA_INTERNAL_PRECISION (7) | |
36 | ||
f964490f RM |
37 | mp_size_t |
38 | __mpn_extract_long_double (mp_ptr res_ptr, mp_size_t size, | |
39 | int *expt, int *is_neg, | |
40 | long double value) | |
41 | { | |
42 | union ibm_extended_long_double u; | |
43 | unsigned long long hi, lo; | |
44 | int ediff; | |
4cf69995 | 45 | |
9605ca6c | 46 | u.ld = value; |
f964490f | 47 | |
9605ca6c AM |
48 | *is_neg = u.d[0].ieee.negative; |
49 | *expt = (int) u.d[0].ieee.exponent - IEEE754_DOUBLE_BIAS; | |
f964490f | 50 | |
9605ca6c AM |
51 | lo = ((long long) u.d[1].ieee.mantissa0 << 32) | u.d[1].ieee.mantissa1; |
52 | hi = ((long long) u.d[0].ieee.mantissa0 << 32) | u.d[0].ieee.mantissa1; | |
4cf69995 | 53 | |
37a4c70b PM |
54 | /* Hold 7 extra bits of precision in the mantissa. This allows |
55 | the normalizing shifts below to prevent losing precision when | |
56 | the signs differ and the exponents are sufficiently far apart. */ | |
57 | lo <<= EXTRA_INTERNAL_PRECISION; | |
58 | ||
4cf69995 | 59 | /* If the lower double is not a denormal or zero then set the hidden |
f964490f | 60 | 53rd bit. */ |
4cf69995 | 61 | if (u.d[1].ieee.exponent != 0) |
37a4c70b | 62 | lo |= 1ULL << (52 + EXTRA_INTERNAL_PRECISION); |
4cf69995 AM |
63 | else |
64 | lo = lo << 1; | |
f964490f | 65 | |
4cf69995 AM |
66 | /* The lower double is normalized separately from the upper. We may |
67 | need to adjust the lower manitissa to reflect this. */ | |
68 | ediff = u.d[0].ieee.exponent - u.d[1].ieee.exponent - 53; | |
69 | if (ediff > 0) | |
70 | { | |
71 | if (ediff < 64) | |
72 | lo = lo >> ediff; | |
73 | else | |
74 | lo = 0; | |
f964490f | 75 | } |
4cf69995 AM |
76 | else if (ediff < 0) |
77 | lo = lo << -ediff; | |
78 | ||
f964490f RM |
79 | /* The high double may be rounded and the low double reflects the |
80 | difference between the long double and the rounded high double | |
81 | value. This is indicated by a differnce between the signs of the | |
82 | high and low doubles. */ | |
4cf69995 AM |
83 | if (u.d[0].ieee.negative != u.d[1].ieee.negative |
84 | && lo != 0) | |
f964490f | 85 | { |
37a4c70b | 86 | lo = (1ULL << (53 + EXTRA_INTERNAL_PRECISION)) - lo; |
4cf69995 | 87 | if (hi == 0) |
f964490f RM |
88 | { |
89 | /* we have a borrow from the hidden bit, so shift left 1. */ | |
37a4c70b PM |
90 | hi = 0x000ffffffffffffeLL | (lo >> (52 + EXTRA_INTERNAL_PRECISION)); |
91 | lo = 0x0fffffffffffffffLL & (lo << 1); | |
f964490f RM |
92 | (*expt)--; |
93 | } | |
94 | else | |
95 | hi--; | |
96 | } | |
97 | #if BITS_PER_MP_LIMB == 32 | |
98 | /* Combine the mantissas to be contiguous. */ | |
37a4c70b PM |
99 | res_ptr[0] = lo >> EXTRA_INTERNAL_PRECISION; |
100 | res_ptr[1] = (hi << (53 - 32)) | (lo >> (32 + EXTRA_INTERNAL_PRECISION)); | |
f964490f RM |
101 | res_ptr[2] = hi >> 11; |
102 | res_ptr[3] = hi >> (32 + 11); | |
103 | #define N 4 | |
104 | #elif BITS_PER_MP_LIMB == 64 | |
105 | /* Combine the two mantissas to be contiguous. */ | |
37a4c70b | 106 | res_ptr[0] = (hi << 53) | (lo >> EXTRA_INTERNAL_PRECISION); |
f964490f RM |
107 | res_ptr[1] = hi >> 11; |
108 | #define N 2 | |
109 | #else | |
110 | #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for" | |
111 | #endif | |
112 | /* The format does not fill the last limb. There are some zeros. */ | |
113 | #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \ | |
114 | - (LDBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB))) | |
115 | ||
9605ca6c | 116 | if (u.d[0].ieee.exponent == 0) |
f964490f RM |
117 | { |
118 | /* A biased exponent of zero is a special case. | |
119 | Either it is a zero or it is a denormal number. */ | |
120 | if (res_ptr[0] == 0 && res_ptr[1] == 0 | |
121 | && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4. */ | |
122 | /* It's zero. */ | |
123 | *expt = 0; | |
124 | else | |
125 | { | |
126 | /* It is a denormal number, meaning it has no implicit leading | |
7e0d315d AS |
127 | one bit, and its exponent is in fact the format minimum. We |
128 | use DBL_MIN_EXP instead of LDBL_MIN_EXP below because the | |
129 | latter describes the properties of both parts together, but | |
130 | the exponent is computed from the high part only. */ | |
f964490f RM |
131 | int cnt; |
132 | ||
133 | #if N == 2 | |
134 | if (res_ptr[N - 1] != 0) | |
135 | { | |
136 | count_leading_zeros (cnt, res_ptr[N - 1]); | |
137 | cnt -= NUM_LEADING_ZEROS; | |
138 | res_ptr[N - 1] = res_ptr[N - 1] << cnt | |
139 | | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt)); | |
140 | res_ptr[0] <<= cnt; | |
7e0d315d | 141 | *expt = DBL_MIN_EXP - 1 - cnt; |
f964490f RM |
142 | } |
143 | else | |
144 | { | |
145 | count_leading_zeros (cnt, res_ptr[0]); | |
146 | if (cnt >= NUM_LEADING_ZEROS) | |
147 | { | |
148 | res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS); | |
149 | res_ptr[0] = 0; | |
150 | } | |
151 | else | |
152 | { | |
153 | res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt); | |
154 | res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt); | |
155 | } | |
7e0d315d | 156 | *expt = DBL_MIN_EXP - 1 |
f964490f RM |
157 | - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt; |
158 | } | |
159 | #else | |
160 | int j, k, l; | |
161 | ||
162 | for (j = N - 1; j > 0; j--) | |
163 | if (res_ptr[j] != 0) | |
164 | break; | |
165 | ||
166 | count_leading_zeros (cnt, res_ptr[j]); | |
167 | cnt -= NUM_LEADING_ZEROS; | |
168 | l = N - 1 - j; | |
169 | if (cnt < 0) | |
170 | { | |
171 | cnt += BITS_PER_MP_LIMB; | |
172 | l--; | |
173 | } | |
174 | if (!cnt) | |
175 | for (k = N - 1; k >= l; k--) | |
176 | res_ptr[k] = res_ptr[k-l]; | |
177 | else | |
178 | { | |
179 | for (k = N - 1; k > l; k--) | |
180 | res_ptr[k] = res_ptr[k-l] << cnt | |
181 | | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt); | |
182 | res_ptr[k--] = res_ptr[0] << cnt; | |
183 | } | |
184 | ||
185 | for (; k >= 0; k--) | |
186 | res_ptr[k] = 0; | |
7e0d315d | 187 | *expt = DBL_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt; |
f964490f RM |
188 | #endif |
189 | } | |
190 | } | |
191 | else | |
192 | /* Add the implicit leading one bit for a normalized number. */ | |
193 | res_ptr[N - 1] |= (mp_limb_t) 1 << (LDBL_MANT_DIG - 1 | |
194 | - ((N - 1) * BITS_PER_MP_LIMB)); | |
195 | ||
196 | return N; | |
197 | } |