1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
|
/* Copyright (C) 1993, 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Library General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with the GNU C Library; see the file COPYING.LIB. If not,
write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA. */
#include "gmp.h"
#include "gmp-impl.h"
#include "longlong.h"
#include "ieee754.h"
#include <float.h>
#include <stdlib.h>
/* Convert a `double' in IEEE754 standard double-precision format to a
multi-precision integer representing the significand scaled up by its
number of bits (52 for double) and an integral power of two (MPN frexp). */
mp_size_t
__mpn_extract_double (mp_ptr res_ptr, mp_size_t size,
int *expt, int *is_neg,
double value)
{
union ieee754_double u;
u.d = value;
*is_neg = u.ieee.negative;
*expt = (int) u.ieee.exponent - IEEE754_DOUBLE_BIAS;
#if BITS_PER_MP_LIMB == 32
res_ptr[0] = u.ieee.mantissa1; /* Low-order 32 bits of fraction. */
res_ptr[1] = u.ieee.mantissa0; /* High-order 20 bits. */
#define N 2
#elif BITS_PER_MP_LIMB == 64
/* Hopefully the compiler will combine the two bitfield extracts
and this composition into just the original quadword extract. */
res_ptr[0] = ((unsigned long int) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
#define N 1
#else
#error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
#endif
/* The format does not fill the last limb. There are some zeros. */
#define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
- (DBL_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
if (u.ieee.exponent == 0)
{
/* A biased exponent of zero is a special case.
Either it is a zero or it is a denormal number. */
if (res_ptr[0] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=2. */
/* It's zero. */
*expt = 0;
else
{
/* It is a denormal number, meaning it has no implicit leading
one bit, and its exponent is in fact the format minimum. */
int cnt;
if (res_ptr[N - 1] != 0)
{
count_leading_zeros (cnt, res_ptr[N - 1]);
cnt -= NUM_LEADING_ZEROS;
#if N == 2
res_ptr[N - 1] = res_ptr[1] << cnt
| (N - 1)
* (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
res_ptr[0] <<= cnt;
#else
res_ptr[N - 1] <<= cnt;
#endif
*expt = DBL_MIN_EXP - 1 - cnt;
}
else
{
count_leading_zeros (cnt, res_ptr[0]);
if (cnt >= NUM_LEADING_ZEROS)
{
res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
res_ptr[0] = 0;
}
else
{
res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
}
*expt = DBL_MIN_EXP - 1
- (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
}
}
}
else
/* Add the implicit leading one bit for a normalized number. */
res_ptr[N - 1] |= 1L << (DBL_MANT_DIG - 1 - ((N - 1) * BITS_PER_MP_LIMB));
return N;
}
|
