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
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
|
/* $NetBSD: n_pow.c,v 1.1 1995/10/10 23:37:02 ragge Exp $ */
/*
* Copyright (c) 1985, 1993
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
* 4. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#ifndef lint
static char sccsid[] = "@(#)pow.c 8.1 (Berkeley) 6/4/93";
#endif /* not lint */
/* POW(X,Y)
* RETURN X**Y
* DOUBLE PRECISION (VAX D format 56 bits, IEEE DOUBLE 53 BITS)
* CODED IN C BY K.C. NG, 1/8/85;
* REVISED BY K.C. NG on 7/10/85.
* KERNEL pow_P() REPLACED BY P. McILROY 7/22/92.
* Required system supported functions:
* scalb(x,n)
* logb(x)
* copysign(x,y)
* finite(x)
* drem(x,y)
*
* Required kernel functions:
* exp__D(a,c) exp(a + c) for |a| << |c|
* struct d_double dlog(x) r.a + r.b, |r.b| < |r.a|
*
* Method
* 1. Compute and return log(x) in three pieces:
* log(x) = n*ln2 + hi + lo,
* where n is an integer.
* 2. Perform y*log(x) by simulating muti-precision arithmetic and
* return the answer in three pieces:
* y*log(x) = m*ln2 + hi + lo,
* where m is an integer.
* 3. Return x**y = exp(y*log(x))
* = 2^m * ( exp(hi+lo) ).
*
* Special cases:
* (anything) ** 0 is 1 ;
* (anything) ** 1 is itself;
* (anything) ** NaN is NaN;
* NaN ** (anything except 0) is NaN;
* +(anything > 1) ** +INF is +INF;
* -(anything > 1) ** +INF is NaN;
* +-(anything > 1) ** -INF is +0;
* +-(anything < 1) ** +INF is +0;
* +(anything < 1) ** -INF is +INF;
* -(anything < 1) ** -INF is NaN;
* +-1 ** +-INF is NaN and signal INVALID;
* +0 ** +(anything except 0, NaN) is +0;
* -0 ** +(anything except 0, NaN, odd integer) is +0;
* +0 ** -(anything except 0, NaN) is +INF and signal DIV-BY-ZERO;
* -0 ** -(anything except 0, NaN, odd integer) is +INF with signal;
* -0 ** (odd integer) = -( +0 ** (odd integer) );
* +INF ** +(anything except 0,NaN) is +INF;
* +INF ** -(anything except 0,NaN) is +0;
* -INF ** (odd integer) = -( +INF ** (odd integer) );
* -INF ** (even integer) = ( +INF ** (even integer) );
* -INF ** -(anything except integer,NaN) is NaN with signal;
* -(x=anything) ** (k=integer) is (-1)**k * (x ** k);
* -(anything except 0) ** (non-integer) is NaN with signal;
*
* Accuracy:
* pow(x,y) returns x**y nearly rounded. In particular, on a SUN, a VAX,
* and a Zilog Z8000,
* pow(integer,integer)
* always returns the correct integer provided it is representable.
* In a test run with 100,000 random arguments with 0 < x, y < 20.0
* on a VAX, the maximum observed error was 1.79 ulps (units in the
* last place).
*
* Constants :
* The hexadecimal values are the intended ones for the following constants.
* The decimal values may be used, provided that the compiler will convert
* from decimal to binary accurately enough to produce the hexadecimal values
* shown.
*/
#include <errno.h>
#include <math.h>
#include "mathimpl.h"
#if (defined(__vax__) || defined(tahoe))
#define TRUNC(x) x = (double) (float) x
#define _IEEE 0
#else
#define _IEEE 1
#define endian (((*(int *) &one)) ? 1 : 0)
#define TRUNC(x) *(((int *) &x)+endian) &= 0xf8000000
#define infnan(x) 0.0
#endif /* vax or tahoe */
const static double zero=0.0, one=1.0, two=2.0, negone= -1.0;
static double pow_P __P((double, double));
double pow(x,y)
double x,y;
{
double t;
if (y==zero)
return (one);
else if (y==one || (_IEEE && x != x))
return (x); /* if x is NaN or y=1 */
else if (_IEEE && y!=y) /* if y is NaN */
return (y);
else if (!finite(y)) /* if y is INF */
if ((t=fabs(x))==one) /* +-1 ** +-INF is NaN */
return (y - y);
else if (t>one)
return ((y<0)? zero : ((x<zero)? y-y : y));
else
return ((y>0)? zero : ((x<0)? y-y : -y));
else if (y==two)
return (x*x);
else if (y==negone)
return (one/x);
/* x > 0, x == +0 */
else if (copysign(one, x) == one)
return (pow_P(x, y));
/* sign(x)= -1 */
/* if y is an even integer */
else if ( (t=drem(y,two)) == zero)
return (pow_P(-x, y));
/* if y is an odd integer */
else if (copysign(t,one) == one)
return (-pow_P(-x, y));
/* Henceforth y is not an integer */
else if (x==zero) /* x is -0 */
return ((y>zero)? -x : one/(-x));
else if (_IEEE)
return (zero/zero);
else
return (infnan(EDOM));
}
/* kernel function for x >= 0 */
static double
#ifdef _ANSI_SOURCE
pow_P(double x, double y)
#else
pow_P(x, y) double x, y;
#endif
{
struct Double s, t, __log__D();
double __exp__D(), huge = 1e300, tiny = 1e-300;
if (x == zero)
if (y > zero)
return (zero);
else if (_IEEE)
return (huge*huge);
else
return (infnan(ERANGE));
if (x == one)
return (one);
if (!finite(x))
if (y < zero)
return (zero);
else if (_IEEE)
return (huge*huge);
else
return (infnan(ERANGE));
if (y >= 7e18) /* infinity */
if (x < 1)
return(tiny*tiny);
else if (_IEEE)
return (huge*huge);
else
return (infnan(ERANGE));
/* Return exp(y*log(x)), using simulated extended */
/* precision for the log and the multiply. */
s = __log__D(x);
t.a = y;
TRUNC(t.a);
t.b = y - t.a;
t.b = s.b*y + t.b*s.a;
t.a *= s.a;
s.a = t.a + t.b;
s.b = (t.a - s.a) + t.b;
return (__exp__D(s.a, s.b));
}
|
