1 /* Copyright (C) 1993, 1994, 1995, 1996, 1997 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, write to the Free
16 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
17 02111-1307 USA. */
18
19 #include "gmp.h"
20 #include "gmp-impl.h"
21 #include "longlong.h"
22 #include <ieee754.h>
23 #include <float.h>
24 #include <stdlib.h>
25
26 /* Convert a `double' in IEEE754 standard double-precision format to a
27 multi-precision integer representing the significand scaled up by its
28 number of bits (52 for double) and an integral power of two (MPN frexp). */
29
30 mp_size_t
__mpn_extract_double(mp_ptr res_ptr,mp_size_t size,int * expt,int * is_neg,double value)31 __mpn_extract_double (mp_ptr res_ptr, mp_size_t size,
32 int *expt, int *is_neg,
33 double value)
34 {
35 union ieee754_double u;
36 u.d = value;
37
38 *is_neg = u.ieee.negative;
39 *expt = (int) u.ieee.exponent - IEEE754_DOUBLE_BIAS;
40
41 #if BITS_PER_MP_LIMB == 32
42 res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction. */
43 res_ptr[1] = u.ieee.mantissa0; /* High-order 20 bits. */
44 #define N 2
45 #elif BITS_PER_MP_LIMB == 64
46 /* Hopefully the compiler will combine the two bitfield extracts
47 and this composition into just the original quadword extract. */
48 res_ptr[0] = ((unsigned long int) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
49 #define N 1
50 #else
51 #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
52 #endif
53 /* The format does not fill the last limb. There are some zeros. */
54 #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
55 - (DBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
56
57 if (u.ieee.exponent == 0)
58 {
59 /* A biased exponent of zero is a special case.
60 Either it is a zero or it is a denormal number. */
61 if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2. */
62 /* It's zero. */
63 *expt = 0;
64 else
65 {
66 /* It is a denormal number, meaning it has no implicit leading
67 one bit, and its exponent is in fact the format minimum. */
68 int cnt;
69
70 if (res_ptr[N - 1] != 0)
71 {
72 count_leading_zeros (cnt, res_ptr[N - 1]);
73 cnt -= NUM_LEADING_ZEROS;
74 #if N == 2
75 res_ptr[N - 1] = res_ptr[1] << cnt
76 | (N - 1)
77 * (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
78 res_ptr[0] <<= cnt;
79 #else
80 res_ptr[N - 1] <<= cnt;
81 #endif
82 *expt = DBL_MIN_EXP - 1 - cnt;
83 }
84 else
85 {
86 count_leading_zeros (cnt, res_ptr[0]);
87 if (cnt >= NUM_LEADING_ZEROS)
88 {
89 res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
90 res_ptr[0] = 0;
91 }
92 else
93 {
94 res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
95 res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
96 }
97 *expt = DBL_MIN_EXP - 1
98 - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
99 }
100 }
101 }
102 else
103 /* Add the implicit leading one bit for a normalized number. */
104 res_ptr[N - 1] |= 1L << (DBL_MANT_DIG - 1 - ((N - 1) * BITS_PER_MP_LIMB));
105
106 return N;
107 }
108