1 /* Copyright (C) 1995,1996,1997,1998,1999,2002,2003
2 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, write to the Free
17 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
18 02111-1307 USA. */
19
20 #include <float.h>
21 #include <math.h>
22 #include <stdlib.h>
23 #include "gmp-impl.h"
24
25 /* Convert a `__float128' in IEEE854 quad-precision format to a
26 multi-precision integer representing the significand scaled up by its
27 number of bits (113 for long double) and an integral power of two
28 (MPN frexpl). */
29
30 mp_size_t
31 mpn_extract_flt128 (mp_ptr res_ptr, mp_size_t size,
32 int *expt, int *is_neg,
33 __float128 value)
34 {
35 ieee854_float128 u;
36 u.value = value;
37
38 *is_neg = u.ieee.negative;
39 *expt = (int) u.ieee.exponent - IEEE854_FLOAT128_BIAS;
40
41 #if BITS_PER_MP_LIMB == 32
42 res_ptr[0] = u.ieee.mantissa3; /* Low-order 32 bits of fraction. */
43 res_ptr[1] = u.ieee.mantissa2;
44 res_ptr[2] = u.ieee.mantissa1;
45 res_ptr[3] = u.ieee.mantissa0; /* High-order 32 bits. */
46 #define N 4
47 #elif BITS_PER_MP_LIMB == 64
48 res_ptr[0] = ((mp_limb_t) u.ieee.mantissa2 << 32) | u.ieee.mantissa3;
49 res_ptr[1] = ((mp_limb_t) u.ieee.mantissa0 << 32) | u.ieee.mantissa1;
50 #define N 2
51 #else
52 #error "mp_limb size " BITS_PER_MP_LIMB "not accounted for"
53 #endif
54 /* The format does not fill the last limb. There are some zeros. */
55 #define NUM_LEADING_ZEROS (BITS_PER_MP_LIMB \
56 - (FLT128_MANT_DIG - ((N - 1) * BITS_PER_MP_LIMB)))
57
58 if (u.ieee.exponent == 0)
59 {
60 /* A biased exponent of zero is a special case.
61 Either it is a zero or it is a denormal number. */
62 if (res_ptr[0] == 0 && res_ptr[1] == 0
63 && res_ptr[N - 2] == 0 && res_ptr[N - 1] == 0) /* Assumes N<=4. */
64 /* It's zero. */
65 *expt = 0;
66 else
67 {
68 /* It is a denormal number, meaning it has no implicit leading
69 one bit, and its exponent is in fact the format minimum. */
70 int cnt;
71
72 #if N == 2
73 if (res_ptr[N - 1] != 0)
74 {
75 count_leading_zeros (cnt, res_ptr[N - 1]);
76 cnt -= NUM_LEADING_ZEROS;
77 res_ptr[N - 1] = res_ptr[N - 1] << cnt
78 | (res_ptr[0] >> (BITS_PER_MP_LIMB - cnt));
79 res_ptr[0] <<= cnt;
80 *expt = FLT128_MIN_EXP - 1 - cnt;
81 }
82 else
83 {
84 count_leading_zeros (cnt, res_ptr[0]);
85 if (cnt >= NUM_LEADING_ZEROS)
86 {
87 res_ptr[N - 1] = res_ptr[0] << (cnt - NUM_LEADING_ZEROS);
88 res_ptr[0] = 0;
89 }
90 else
91 {
92 res_ptr[N - 1] = res_ptr[0] >> (NUM_LEADING_ZEROS - cnt);
93 res_ptr[0] <<= BITS_PER_MP_LIMB - (NUM_LEADING_ZEROS - cnt);
94 }
95 *expt = FLT128_MIN_EXP - 1
96 - (BITS_PER_MP_LIMB - NUM_LEADING_ZEROS) - cnt;
97 }
98 #else
99 int j, k, l;
100
101 for (j = N - 1; j > 0; j--)
102 if (res_ptr[j] != 0)
103 break;
104
105 count_leading_zeros (cnt, res_ptr[j]);
106 cnt -= NUM_LEADING_ZEROS;
107 l = N - 1 - j;
108 if (cnt < 0)
109 {
110 cnt += BITS_PER_MP_LIMB;
111 l--;
112 }
113 if (!cnt)
114 for (k = N - 1; k >= l; k--)
115 res_ptr[k] = res_ptr[k-l];
116 else
117 {
118 for (k = N - 1; k > l; k--)
119 res_ptr[k] = res_ptr[k-l] << cnt
120 | res_ptr[k-l-1] >> (BITS_PER_MP_LIMB - cnt);
121 res_ptr[k--] = res_ptr[0] << cnt;
122 }
123
124 for (; k >= 0; k--)
125 res_ptr[k] = 0;
126 *expt = FLT128_MIN_EXP - 1 - l * BITS_PER_MP_LIMB - cnt;
127 #endif
128 }
129 }
130 else
131 /* Add the implicit leading one bit for a normalized number. */
132 res_ptr[N - 1] |= (mp_limb_t) 1 << (FLT128_MANT_DIG - 1
133 - ((N - 1) * BITS_PER_MP_LIMB));
134
135 return N;
136 }