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1.1 maekawa 1: /* __gmp_extract_double -- convert from double to array of mp_limb_t.
2:
3: Copyright (C) 1996 Free Software Foundation, Inc.
4:
5: This file is part of the GNU MP Library.
6:
7: The GNU MP Library is free software; you can redistribute it and/or modify
8: it under the terms of the GNU Library General Public License as published by
9: the Free Software Foundation; either version 2 of the License, or (at your
10: option) any later version.
11:
12: The GNU MP Library is distributed in the hope that it will be useful, but
13: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14: or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
15: License for more details.
16:
17: You should have received a copy of the GNU Library General Public License
18: along with the GNU MP Library; see the file COPYING.LIB. If not, write to
19: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
20: MA 02111-1307, USA. */
21:
22: #include "gmp.h"
23: #include "gmp-impl.h"
24:
25: #ifdef XDEBUG
26: #undef _GMP_IEEE_FLOATS
27: #endif
28:
29: #ifndef _GMP_IEEE_FLOATS
30: #define _GMP_IEEE_FLOATS 0
31: #endif
32:
33: #define MP_BASE_AS_DOUBLE (2.0 * ((mp_limb_t) 1 << (BITS_PER_MP_LIMB - 1)))
34:
35: /* Extract a non-negative double in d. */
36:
37: int
38: #if __STDC__
39: __gmp_extract_double (mp_ptr rp, double d)
40: #else
41: __gmp_extract_double (rp, d)
42: mp_ptr rp;
43: double d;
44: #endif
45: {
46: long exp;
47: unsigned sc;
48: mp_limb_t manh, manl;
49:
50: /* BUGS
51:
52: 1. Should handle Inf and NaN in IEEE specific code.
53: 2. Handle Inf and NaN also in default code, to avoid hangs.
54: 3. Generalize to handle all BITS_PER_MP_LIMB >= 32.
55: 4. This lits is incomplete and misspelled.
56: */
57:
58: if (d == 0.0)
59: {
60: rp[0] = 0;
61: rp[1] = 0;
62: #if BITS_PER_MP_LIMB == 32
63: rp[2] = 0;
64: #endif
65: return 0;
66: }
67:
68: #if _GMP_IEEE_FLOATS
69: {
70: union ieee_double_extract x;
71: x.d = d;
72:
73: exp = x.s.exp;
74: sc = (unsigned) (exp + 2) % BITS_PER_MP_LIMB;
75: #if BITS_PER_MP_LIMB == 64
76: manl = (((mp_limb_t) 1 << 63)
77: | ((mp_limb_t) x.s.manh << 43) | ((mp_limb_t) x.s.manl << 11));
78: #else
79: manh = ((mp_limb_t) 1 << 31) | (x.s.manh << 11) | (x.s.manl >> 21);
80: manl = x.s.manl << 11;
81: #endif
82: }
83: #else
84: {
85: /* Unknown (or known to be non-IEEE) double format. */
86: exp = 0;
87: if (d >= 1.0)
88: {
89: if (d * 0.5 == d)
90: abort ();
91:
92: while (d >= 32768.0)
93: {
94: d *= (1.0 / 65536.0);
95: exp += 16;
96: }
97: while (d >= 1.0)
98: {
99: d *= 0.5;
100: exp += 1;
101: }
102: }
103: else if (d < 0.5)
104: {
105: while (d < (1.0 / 65536.0))
106: {
107: d *= 65536.0;
108: exp -= 16;
109: }
110: while (d < 0.5)
111: {
112: d *= 2.0;
113: exp -= 1;
114: }
115: }
116:
117: sc = (unsigned) exp % BITS_PER_MP_LIMB;
118:
119: d *= MP_BASE_AS_DOUBLE;
120: #if BITS_PER_MP_LIMB == 64
121: manl = d;
122: #else
123: manh = d;
124: manl = (d - manh) * MP_BASE_AS_DOUBLE;
125: #endif
126:
127: exp += 1022;
128: }
129: #endif
130:
131: exp = (unsigned) (exp + 1) / BITS_PER_MP_LIMB - 1024 / BITS_PER_MP_LIMB + 1;
132:
133: #if BITS_PER_MP_LIMB == 64
134: if (sc != 0)
135: {
136: rp[1] = manl >> (BITS_PER_MP_LIMB - sc);
137: rp[0] = manl << sc;
138: }
139: else
140: {
141: rp[1] = manl;
142: rp[0] = 0;
143: }
144: #else
145: if (sc != 0)
146: {
147: rp[2] = manh >> (BITS_PER_MP_LIMB - sc);
148: rp[1] = (manl >> (BITS_PER_MP_LIMB - sc)) | (manh << sc);
149: rp[0] = manl << sc;
150: }
151: else
152: {
153: rp[2] = manh;
154: rp[1] = manl;
155: rp[0] = 0;
156: }
157: #endif
158:
159: return exp;
160: }