/[jscoverage]/trunk/js/src/fdlibm/e_log10.c
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Contents of /trunk/js/src/fdlibm/e_log10.c

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Wed Aug 1 13:51:53 2007 UTC (14 years, 9 months ago) by siliconforks
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Initial import.

1 /* -*- Mode: C; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
2 *
3 * ***** BEGIN LICENSE BLOCK *****
4 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
5 *
6 * The contents of this file are subject to the Mozilla Public License Version
7 * 1.1 (the "License"); you may not use this file except in compliance with
8 * the License. You may obtain a copy of the License at
9 * http://www.mozilla.org/MPL/
10 *
11 * Software distributed under the License is distributed on an "AS IS" basis,
12 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
13 * for the specific language governing rights and limitations under the
14 * License.
15 *
16 * The Original Code is Mozilla Communicator client code, released
17 * March 31, 1998.
18 *
19 * The Initial Developer of the Original Code is
20 * Sun Microsystems, Inc.
21 * Portions created by the Initial Developer are Copyright (C) 1998
22 * the Initial Developer. All Rights Reserved.
23 *
24 * Contributor(s):
25 *
26 * Alternatively, the contents of this file may be used under the terms of
27 * either of the GNU General Public License Version 2 or later (the "GPL"),
28 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
29 * in which case the provisions of the GPL or the LGPL are applicable instead
30 * of those above. If you wish to allow use of your version of this file only
31 * under the terms of either the GPL or the LGPL, and not to allow others to
32 * use your version of this file under the terms of the MPL, indicate your
33 * decision by deleting the provisions above and replace them with the notice
34 * and other provisions required by the GPL or the LGPL. If you do not delete
35 * the provisions above, a recipient may use your version of this file under
36 * the terms of any one of the MPL, the GPL or the LGPL.
37 *
38 * ***** END LICENSE BLOCK ***** */
39
40 /* @(#)e_log10.c 1.3 95/01/18 */
41 /*
42 * ====================================================
43 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
44 *
45 * Developed at SunSoft, a Sun Microsystems, Inc. business.
46 * Permission to use, copy, modify, and distribute this
47 * software is freely granted, provided that this notice
48 * is preserved.
49 * ====================================================
50 */
51
52 /* __ieee754_log10(x)
53 * Return the base 10 logarithm of x
54 *
55 * Method :
56 * Let log10_2hi = leading 40 bits of log10(2) and
57 * log10_2lo = log10(2) - log10_2hi,
58 * ivln10 = 1/log(10) rounded.
59 * Then
60 * n = ilogb(x),
61 * if(n<0) n = n+1;
62 * x = scalbn(x,-n);
63 * log10(x) := n*log10_2hi + (n*log10_2lo + ivln10*log(x))
64 *
65 * Note 1:
66 * To guarantee log10(10**n)=n, where 10**n is normal, the rounding
67 * mode must set to Round-to-Nearest.
68 * Note 2:
69 * [1/log(10)] rounded to 53 bits has error .198 ulps;
70 * log10 is monotonic at all binary break points.
71 *
72 * Special cases:
73 * log10(x) is NaN with signal if x < 0;
74 * log10(+INF) is +INF with no signal; log10(0) is -INF with signal;
75 * log10(NaN) is that NaN with no signal;
76 * log10(10**N) = N for N=0,1,...,22.
77 *
78 * Constants:
79 * The hexadecimal values are the intended ones for the following constants.
80 * The decimal values may be used, provided that the compiler will convert
81 * from decimal to binary accurately enough to produce the hexadecimal values
82 * shown.
83 */
84
85 #include "fdlibm.h"
86
87 #ifdef __STDC__
88 static const double
89 #else
90 static double
91 #endif
92 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
93 ivln10 = 4.34294481903251816668e-01, /* 0x3FDBCB7B, 0x1526E50E */
94 log10_2hi = 3.01029995663611771306e-01, /* 0x3FD34413, 0x509F6000 */
95 log10_2lo = 3.69423907715893078616e-13; /* 0x3D59FEF3, 0x11F12B36 */
96
97 static double zero = 0.0;
98
99 #ifdef __STDC__
100 double __ieee754_log10(double x)
101 #else
102 double __ieee754_log10(x)
103 double x;
104 #endif
105 {
106 fd_twoints u;
107 double y,z;
108 int i,k,hx;
109 unsigned lx;
110
111 u.d = x;
112 hx = __HI(u); /* high word of x */
113 lx = __LO(u); /* low word of x */
114
115 k=0;
116 if (hx < 0x00100000) { /* x < 2**-1022 */
117 if (((hx&0x7fffffff)|lx)==0)
118 return -two54/zero; /* log(+-0)=-inf */
119 if (hx<0) return (x-x)/zero; /* log(-#) = NaN */
120 k -= 54; x *= two54; /* subnormal number, scale up x */
121 u.d = x;
122 hx = __HI(u); /* high word of x */
123 }
124 if (hx >= 0x7ff00000) return x+x;
125 k += (hx>>20)-1023;
126 i = ((unsigned)k&0x80000000)>>31;
127 hx = (hx&0x000fffff)|((0x3ff-i)<<20);
128 y = (double)(k+i);
129 u.d = x;
130 __HI(u) = hx;
131 x = u.d;
132 z = y*log10_2lo + ivln10*__ieee754_log(x);
133 return z+y*log10_2hi;
134 }

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