1 /* $NetBSD: ldexp_ieee754.c,v 1.4 2003/12/30 23:19:07 martin Exp $ */
2
3 /*-
4 * Copyright (c) 1999 The NetBSD Foundation, Inc.
5 * All rights reserved.
6 *
7 * This code is derived from software contributed to The NetBSD Foundation
8 * by Charles M. Hannum.
9 *
10 * Redistribution and use in source and binary forms, with or without
11 * modification, are permitted provided that the following conditions
12 * are met:
13 * 1. Redistributions of source code must retain the above copyright
14 * notice, this list of conditions and the following disclaimer.
15 * 2. Redistributions in binary form must reproduce the above copyright
16 * notice, this list of conditions and the following disclaimer in the
17 * documentation and/or other materials provided with the distribution.
18 * 3. All advertising materials mentioning features or use of this software
19 * must display the following acknowledgement:
20 * This product includes software developed by the NetBSD
21 * Foundation, Inc. and its contributors.
22 * 4. Neither the name of The NetBSD Foundation nor the names of its
23 * contributors may be used to endorse or promote products derived
24 * from this software without specific prior written permission.
25 *
26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
36 * POSSIBILITY OF SUCH DAMAGE.
37 */
38
39 #include <sys/cdefs.h>
40 #if defined(LIBC_SCCS) && !defined(lint)
41 __RCSID("$MirOS: src/lib/libc/gen/ldexp_ieee754.c,v 1.2 2006/11/03 18:10:44 tg Exp $");
42 __RCSID("$NetBSD: ldexp_ieee754.c,v 1.4 2003/12/30 23:19:07 martin Exp $");
43 #endif /* LIBC_SCCS and not lint */
44
45 #include <sys/types.h>
46 #include <machine/ieee.h>
47 #include <errno.h>
48 #include <math.h>
49
50 /*
51 * Multiply the given value by 2^expon.
52 */
53 double
ldexp(double val,int expon)54 ldexp(double val, int expon)
55 {
56 int oldexp, newexp;
57 union ieee_double_u u, mul;
58
59 u.dblu_d = val;
60 oldexp = u.dblu_dbl.dbl_exp;
61
62 /*
63 * If input is zero, Inf or NaN, just return it.
64 */
65 if (u.dblu_d == 0.0 || oldexp == DBL_EXP_INFNAN)
66 return (val);
67
68 if (oldexp == 0) {
69 /*
70 * u.v is denormal. We must adjust it so that the exponent
71 * arithmetic below will work.
72 */
73 if (expon <= DBL_EXP_BIAS) {
74 /*
75 * Optimization: if the scaling can be done in a single
76 * multiply, or underflows, just do it now.
77 */
78 if (expon <= -DBL_FRACBITS) {
79 errno = ERANGE;
80 return (val < 0.0 ? -0.0 : 0.0);
81 }
82 mul.dblu_d = 0.0;
83 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS;
84 u.dblu_d *= mul.dblu_d;
85 if (u.dblu_d == 0.0) {
86 errno = ERANGE;
87 return (val < 0.0 ? -0.0 : 0.0);
88 }
89 return (u.dblu_d);
90 } else {
91 /*
92 * We know that expon is very large, and therefore the
93 * result cannot be denormal (though it may be Inf).
94 * Shift u.v by just enough to make it normal.
95 */
96 mul.dblu_d = 0.0;
97 mul.dblu_dbl.dbl_exp = DBL_FRACBITS + DBL_EXP_BIAS;
98 u.dblu_d *= mul.dblu_d;
99 expon -= DBL_FRACBITS;
100 oldexp = u.dblu_dbl.dbl_exp;
101 }
102 }
103
104 /*
105 * u.v is now normalized and oldexp has been adjusted if necessary.
106 * Calculate the new exponent and check for underflow and overflow.
107 */
108 newexp = oldexp + expon;
109
110 if (newexp <= 0) {
111 /*
112 * The output number is either denormal or underflows (see
113 * comments in machine/ieee.h).
114 */
115 if (newexp <= -DBL_FRACBITS) {
116 errno = ERANGE;
117 return (val < 0.0 ? -0.0 : 0.0);
118 }
119 /*
120 * Denormalize the result. We do this with a multiply. If
121 * expon is very large, it won't fit in a double, so we have
122 * to adjust the exponent first. This is safe because we know
123 * that u.v is normal at this point.
124 */
125 if (expon <= -DBL_EXP_BIAS) {
126 u.dblu_dbl.dbl_exp = 1;
127 expon += oldexp - 1;
128 }
129 mul.dblu_d = 0.0;
130 mul.dblu_dbl.dbl_exp = expon + DBL_EXP_BIAS;
131 u.dblu_d *= mul.dblu_d;
132 return (u.dblu_d);
133 } else if (newexp >= DBL_EXP_INFNAN) {
134 /*
135 * The result overflowed; return +/-Inf.
136 */
137 u.dblu_dbl.dbl_exp = DBL_EXP_INFNAN;
138 u.dblu_dbl.dbl_frach = 0;
139 u.dblu_dbl.dbl_fracl = 0;
140 errno = ERANGE;
141 return (u.dblu_d);
142 } else {
143 /*
144 * The result is normal; just replace the old exponent with the
145 * new one.
146 */
147 u.dblu_dbl.dbl_exp = newexp;
148 return (u.dblu_d);
149 }
150 }
151