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annotate packages/language/c/libm/current/src/double/portable-api/s_cos.c @ 64:c38311975d4f ecos-sw-2000-01-28

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Merge from eCos master repository on 2000-01-28-04:28:11-GMT
author jlarmour
date Fri, 28 Jan 2000 04:59:39 +0000
parents 443894e2e912
children bf00f99aec69
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1 //===========================================================================
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2 //
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3 // s_cos.c
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4 //
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5 // Part of the standard mathematical function library
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6 //
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7 //===========================================================================
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8 //####COPYRIGHTBEGIN####
64
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9 //
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10 // -------------------------------------------
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11 // The contents of this file are subject to the Red Hat eCos Public License
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12 // Version 1.0 (the "License"); you may not use this file except in
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13 // compliance with the License. You may obtain a copy of the License at
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14 // http://sourceware.cygnus.com/ecos
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15 //
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16 // Software distributed under the License is distributed on an
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17 // basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
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18 // License for the specific language governing rights and limitations under
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19 // the License.
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20 //
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21 // The Original Code is eCos - Embedded Configurable Operating System,
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22 // released September 30, 1998.
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23 //
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24 // The Initial Developer of the Original Code is Red Hat.
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25 // Portions created by Red Hat are
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26 // Copyright (C) 1998, 1999, 2000 Red Hat, Inc.
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27 // All Rights Reserved.
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28 // -------------------------------------------
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29 //
0
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30 //####COPYRIGHTEND####
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31 //===========================================================================
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32 //#####DESCRIPTIONBEGIN####
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33 //
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34 // Author(s): jlarmour
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35 // Contributors: jlarmour
0
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36 // Date: 1998-02-13
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37 // Purpose:
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38 // Description:
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39 // Usage:
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40 //
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41 //####DESCRIPTIONEND####
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42 //
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43 //===========================================================================
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44
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45 // CONFIGURATION
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46
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47 #include <pkgconf/libm.h> // Configuration header
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48
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49 // Include the Math library?
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50 #ifdef CYGPKG_LIBM
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51
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52 // Derived from code with the following copyright
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53
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54
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55 /* @(#)s_cos.c 1.3 95/01/18 */
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56 /*
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57 * ====================================================
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58 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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59 *
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60 * Developed at SunSoft, a Sun Microsystems, Inc. business.
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61 * Permission to use, copy, modify, and distribute this
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62 * software is freely granted, provided that this notice
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63 * is preserved.
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64 * ====================================================
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65 */
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66
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67 /* cos(x)
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68 * Return cosine function of x.
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69 *
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70 * kernel function:
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71 * __kernel_sin ... sine function on [-pi/4,pi/4]
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72 * __kernel_cos ... cosine function on [-pi/4,pi/4]
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73 * __ieee754_rem_pio2 ... argument reduction routine
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74 *
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75 * Method.
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76 * Let S,C and T denote the sin, cos and tan respectively on
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77 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
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78 * in [-pi/4 , +pi/4], and let n = k mod 4.
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79 * We have
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80 *
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81 * n sin(x) cos(x) tan(x)
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82 * ----------------------------------------------------------
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83 * 0 S C T
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84 * 1 C -S -1/T
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85 * 2 -S -C T
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86 * 3 -C S -1/T
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87 * ----------------------------------------------------------
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88 *
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89 * Special cases:
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90 * Let trig be any of sin, cos, or tan.
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91 * trig(+-INF) is NaN, with signals;
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92 * trig(NaN) is that NaN;
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93 *
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94 * Accuracy:
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95 * TRIG(x) returns trig(x) nearly rounded
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96 */
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97
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98 #include "mathincl/fdlibm.h"
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99
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100 double cos(double x)
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101 {
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102 double y[2],z=0.0;
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103 int n, ix;
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104
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105 /* High word of x. */
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106 ix = CYG_LIBM_HI(x);
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107
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108 /* |x| ~< pi/4 */
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109 ix &= 0x7fffffff;
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110 if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
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111
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112 /* cos(Inf or NaN) is NaN */
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113 else if (ix>=0x7ff00000) return x-x;
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114
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115 /* argument reduction needed */
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116 else {
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117 n = __ieee754_rem_pio2(x,y);
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118 switch(n&3) {
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119 case 0: return __kernel_cos(y[0],y[1]);
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120 case 1: return -__kernel_sin(y[0],y[1],1);
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121 case 2: return -__kernel_cos(y[0],y[1]);
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122 default:
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123 return __kernel_sin(y[0],y[1],1);
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124 }
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125 }
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126 }
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127
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128 #endif // ifdef CYGPKG_LIBM
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129
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130 // EOF s_cos.c