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04277e02 | 1 | /* Copyright (C) 1993-2019 Free Software Foundation, Inc. |
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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 | |
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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. | |
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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 | |
41bdb6e2 | 12 | Lesser General Public License for more details. |
377a515b | 13 | |
41bdb6e2 | 14 | You should have received a copy of the GNU Lesser General Public |
59ba27a6 | 15 | License along with the GNU C Library; if not, see |
5a82c748 | 16 | <https://www.gnu.org/licenses/>. */ |
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17 | |
18 | #include "gmp.h" | |
19 | #include "gmp-impl.h" | |
20 | #include "longlong.h" | |
981993e1 | 21 | #include <ieee754.h> |
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22 | #include <float.h> |
23 | #include <stdlib.h> | |
24 | ||
25 | /* Convert a `double' in IEEE754 standard double-precision format to a | |
26 | multi-precision integer representing the significand scaled up by its | |
27 | number of bits (52 for double) and an integral power of two (MPN frexp). */ | |
28 | ||
29 | mp_size_t | |
30 | __mpn_extract_double (mp_ptr res_ptr, mp_size_t size, | |
31 | int *expt, int *is_neg, | |
32 | double value) | |
33 | { | |
34 | union ieee754_double u; | |
35 | u.d = value; | |
36 | ||
37 | *is_neg = u.ieee.negative; | |
38 | *expt = (int) u.ieee.exponent - IEEE754_DOUBLE_BIAS; | |
39 | ||
40 | #if BITS_PER_MP_LIMB == 32 | |
41 | res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction. */ | |
42 | res_ptr[1] = u.ieee.mantissa0; /* High-order 20 bits. */ | |
c5d5d574 | 43 | # define N 2 |
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44 | #elif BITS_PER_MP_LIMB == 64 |
45 | /* Hopefully the compiler will combine the two bitfield extracts | |
46 | and this composition into just the original quadword extract. */ | |
d8a5edc2 | 47 | res_ptr[0] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1; |
c5d5d574 | 48 | # define N 1 |
28f540f4 | 49 | #else |
c5d5d574 | 50 | # error "mp_limb size " BITS_PER_MP_LIMB "not accounted for" |
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51 | #endif |
52 | /* The format does not fill the last limb. There are some zeros. */ | |
53 | #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \ | |
54 | - (DBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB))) | |
55 | ||
56 | if (u.ieee.exponent == 0) | |
57 | { | |
58 | /* A biased exponent of zero is a special case. | |
59 | Either it is a zero or it is a denormal number. */ | |
60 | if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2. */ | |
61 | /* It's zero. */ | |
62 | *expt = 0; | |
63 | else | |
64 | { | |
65 | /* It is a denormal number, meaning it has no implicit leading | |
66 | one bit, and its exponent is in fact the format minimum. */ | |
67 | int cnt; | |
68 | ||
69 | if (res_ptr[N - 1] != 0) | |
70 | { | |
71 | count_leading_zeros (cnt, res_ptr[N - 1]); | |
72 | cnt -= NUM_LEADING_ZEROS; | |
73 | #if N == 2 | |
74 | res_ptr[N - 1] = res_ptr[1] << cnt | |
75 | | (N - 1) | |
c5d5d574 | 76 | * (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt)); |
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77 | res_ptr[0] <<= cnt; |
78 | #else | |
79 | res_ptr[N - 1] <<= cnt; | |
80 | #endif | |
81 | *expt = DBL_MIN_EXP - 1 - cnt; | |
82 | } | |
83 | else | |
84 | { | |
85 | count_leading_zeros (cnt, res_ptr[0]); | |
86 | if (cnt >= NUM_LEADING_ZEROS) | |
87 | { | |
88 | res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS); | |
a182affd | 89 | res_ptr[0] = 0; |
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90 | } |
91 | else | |
92 | { | |
93 | res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt); | |
94 | res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt); | |
95 | } | |
96 | *expt = DBL_MIN_EXP - 1 | |
97 | - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt; | |
98 | } | |
99 | } | |
100 | } | |
101 | else | |
102 | /* Add the implicit leading one bit for a normalized number. */ | |
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103 | res_ptr[N - 1] |= (mp_limb_t) 1 << (DBL_MANT_DIG - 1 |
104 | - ((N - 1) * BITS_PER_MP_LIMB)); | |
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105 | |
106 | return N; | |
107 | } |