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comparison packages/language/c/libm/current/src/double/portable-api/s_scalbn.c @ 0:3111d98ba7b3 ecos-v1_1-release

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Initial commit of eCos version 1.1
author jlarmour
date Tue, 11 May 1999 11:16:07 +0000
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children 443894e2e912
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-1:000000000000 0:3111d98ba7b3
1 //===========================================================================
2 //
3 // s_scalbn.c
4 //
5 // Part of the standard mathematical function library
6 //
7 //===========================================================================
8 //####COPYRIGHTBEGIN####
9 //
10 // -------------------------------------------
11 // The contents of this file are subject to the Cygnus eCos Public License
12 // Version 1.0 (the "License"); you may not use this file except in
13 // compliance with the License. You may obtain a copy of the License at
14 // http://sourceware.cygnus.com/ecos
15 //
16 // Software distributed under the License is distributed on an "AS IS"
17 // basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
18 // License for the specific language governing rights and limitations under
19 // the License.
20 //
21 // The Original Code is eCos - Embedded Cygnus Operating System, released
22 // September 30, 1998.
23 //
24 // The Initial Developer of the Original Code is Cygnus. Portions created
25 // by Cygnus are Copyright (C) 1998 Cygnus Solutions. All Rights Reserved.
26 // -------------------------------------------
27 //
28 //####COPYRIGHTEND####
29 //===========================================================================
30 //#####DESCRIPTIONBEGIN####
31 //
32 // Author(s): jlarmour@cygnus.co.uk
33 // Contributors: jlarmour@cygnus.co.uk
34 // Date: 1998-02-13
35 // Purpose:
36 // Description:
37 // Usage:
38 //
39 //####DESCRIPTIONEND####
40 //
41 //===========================================================================
42
43 // CONFIGURATION
44
45 #include <pkgconf/libm.h> // Configuration header
46
47 // Include the Math library?
48 #ifdef CYGPKG_LIBM
49
50 // Derived from code with the following copyright
51
52
53 /* @(#)s_scalbn.c 1.3 95/01/18 */
54 /*
55 * ====================================================
56 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
57 *
58 * Developed at SunSoft, a Sun Microsystems, Inc. business.
59 * Permission to use, copy, modify, and distribute this
60 * software is freely granted, provided that this notice
61 * is preserved.
62 * ====================================================
63 */
64
65 /*
66 * scalbn (double x, int n)
67 * scalbn(x,n) returns x* 2**n computed by exponent
68 * manipulation rather than by actually performing an
69 * exponentiation or a multiplication.
70 */
71
72 #include "mathincl/fdlibm.h"
73
74 static const double
75 two54 = 1.80143985094819840000e+16, /* 0x43500000, 0x00000000 */
76 twom54 = 5.55111512312578270212e-17, /* 0x3C900000, 0x00000000 */
77 huge = 1.0e+300,
78 tiny = 1.0e-300;
79
80 double scalbn (double x, int n)
81 {
82 int k,hx,lx;
83 hx = CYG_LIBM_HI(x);
84 lx = CYG_LIBM_LO(x);
85 k = (hx&0x7ff00000)>>20; /* extract exponent */
86 if (k==0) { /* 0 or subnormal x */
87 if ((lx|(hx&0x7fffffff))==0) return x; /* +-0 */
88 x *= two54;
89 hx = CYG_LIBM_HI(x);
90 k = ((hx&0x7ff00000)>>20) - 54;
91 if (n< -50000) return tiny*x; /*underflow*/
92 }
93 if (k==0x7ff) return x+x; /* NaN or Inf */
94 k = k+n;
95 if (k > 0x7fe) return huge*copysign(huge,x); /* overflow */
96 if (k > 0) /* normal result */
97 {CYG_LIBM_HI(x) = (hx&0x800fffff)|(k<<20); return x;}
98 if (k <= -54) {
99 if (n > 50000) /* in case integer overflow in n+k */
100 return huge*copysign(huge,x); /*overflow*/
101 else return tiny*copysign(tiny,x); /*underflow*/
102 }
103 k += 54; /* subnormal result */
104 CYG_LIBM_HI(x) = (hx&0x800fffff)|(k<<20);
105 return x*twom54;
106 }
107
108 #endif // ifdef CYGPKG_LIBM
109
110 // EOF s_scalbn.c