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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#### |
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9 // |
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10 // ------------------------------------------- |
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11 // The contents of this file are subject to the Cygnus 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 "AS IS" |
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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 Cygnus Operating System, released |
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22 // September 30, 1998. |
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23 // |
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24 // The Initial Developer of the Original Code is Cygnus. Portions created |
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25 // by Cygnus are Copyright (C) 1998 Cygnus Solutions. All Rights Reserved. |
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26 // ------------------------------------------- |
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27 // |
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28 //####COPYRIGHTEND#### |
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29 //=========================================================================== |
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30 //#####DESCRIPTIONBEGIN#### |
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31 // |
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32 // Author(s): jlarmour@cygnus.co.uk |
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33 // Contributors: jlarmour@cygnus.co.uk |
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34 // Date: 1998-02-13 |
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35 // Purpose: |
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36 // Description: |
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37 // Usage: |
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38 // |
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39 //####DESCRIPTIONEND#### |
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40 // |
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41 //=========================================================================== |
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42 |
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43 // CONFIGURATION |
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44 |
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45 #include <pkgconf/libm.h> // Configuration header |
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46 |
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47 // Include the Math library? |
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48 #ifdef CYGPKG_LIBM |
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49 |
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50 // Derived from code with the following copyright |
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51 |
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52 |
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53 /* @(#)s_cos.c 1.3 95/01/18 */ |
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54 /* |
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55 * ==================================================== |
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56 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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57 * |
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58 * Developed at SunSoft, a Sun Microsystems, Inc. business. |
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59 * Permission to use, copy, modify, and distribute this |
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60 * software is freely granted, provided that this notice |
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61 * is preserved. |
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62 * ==================================================== |
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63 */ |
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64 |
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65 /* cos(x) |
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66 * Return cosine function of x. |
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67 * |
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68 * kernel function: |
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69 * __kernel_sin ... sine function on [-pi/4,pi/4] |
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70 * __kernel_cos ... cosine function on [-pi/4,pi/4] |
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71 * __ieee754_rem_pio2 ... argument reduction routine |
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72 * |
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73 * Method. |
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74 * Let S,C and T denote the sin, cos and tan respectively on |
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75 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
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76 * in [-pi/4 , +pi/4], and let n = k mod 4. |
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77 * We have |
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78 * |
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79 * n sin(x) cos(x) tan(x) |
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80 * ---------------------------------------------------------- |
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81 * 0 S C T |
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82 * 1 C -S -1/T |
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83 * 2 -S -C T |
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84 * 3 -C S -1/T |
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85 * ---------------------------------------------------------- |
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86 * |
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87 * Special cases: |
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88 * Let trig be any of sin, cos, or tan. |
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89 * trig(+-INF) is NaN, with signals; |
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90 * trig(NaN) is that NaN; |
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91 * |
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92 * Accuracy: |
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93 * TRIG(x) returns trig(x) nearly rounded |
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94 */ |
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95 |
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96 #include "mathincl/fdlibm.h" |
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97 |
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98 double cos(double x) |
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99 { |
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100 double y[2],z=0.0; |
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101 int n, ix; |
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102 |
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103 /* High word of x. */ |
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104 ix = CYG_LIBM_HI(x); |
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105 |
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106 /* |x| ~< pi/4 */ |
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107 ix &= 0x7fffffff; |
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108 if(ix <= 0x3fe921fb) return __kernel_cos(x,z); |
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109 |
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110 /* cos(Inf or NaN) is NaN */ |
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111 else if (ix>=0x7ff00000) return x-x; |
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112 |
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113 /* argument reduction needed */ |
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114 else { |
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115 n = __ieee754_rem_pio2(x,y); |
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116 switch(n&3) { |
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117 case 0: return __kernel_cos(y[0],y[1]); |
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118 case 1: return -__kernel_sin(y[0],y[1],1); |
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119 case 2: return -__kernel_cos(y[0],y[1]); |
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120 default: |
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121 return __kernel_sin(y[0],y[1],1); |
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122 } |
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123 } |
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124 } |
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125 |
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126 #endif // ifdef CYGPKG_LIBM |
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127 |
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128 // EOF s_cos.c |
