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4349 | Serge | 1 | |
2 | /* |
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3 | * ==================================================== |
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4 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
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5 | * |
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6 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
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7 | * Permission to use, copy, modify, and distribute this |
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8 | * software is freely granted, provided that this notice |
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9 | * is preserved. |
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10 | * ==================================================== |
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11 | */ |
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12 | |||
13 | |||
14 | * Return cosine function of x. |
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15 | * |
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16 | * kernel function: |
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17 | * __kernel_sin ... sine function on [-pi/4,pi/4] |
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18 | * __kernel_cos ... cosine function on [-pi/4,pi/4] |
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19 | * __ieee754_rem_pio2 ... argument reduction routine |
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20 | * |
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21 | * Method. |
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22 | * Let S,C and T denote the sin, cos and tan respectively on |
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23 | * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 |
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24 | * in [-pi/4 , +pi/4], and let n = k mod 4. |
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25 | * We have |
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26 | * |
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27 | * n sin(x) cos(x) tan(x) |
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28 | * ---------------------------------------------------------- |
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29 | * 0 S C T |
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30 | * 1 C -S -1/T |
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31 | * 2 -S -C T |
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32 | * 3 -C S -1/T |
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33 | * ---------------------------------------------------------- |
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34 | * |
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35 | * Special cases: |
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36 | * Let trig be any of sin, cos, or tan. |
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37 | * trig(+-INF) is NaN, with signals; |
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38 | * trig(NaN) is that NaN; |
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39 | * |
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40 | * Accuracy: |
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41 | * TRIG(x) returns trig(x) nearly rounded |
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42 | */ |
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43 | |||
44 | |||
45 | |||
46 | |||
47 | |||
48 | |||
49 | double cos(double x) |
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50 | #else |
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51 | double cos(x) |
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52 | double x; |
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53 | #endif |
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54 | { |
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55 | double y[2],z=0.0; |
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56 | __int32_t n,ix; |
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57 | |||
58 | |||
59 | GET_HIGH_WORD(ix,x); |
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60 | |||
61 | |||
62 | ix &= 0x7fffffff; |
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63 | if(ix <= 0x3fe921fb) return __kernel_cos(x,z); |
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64 | |||
65 | |||
66 | else if (ix>=0x7ff00000) return x-x; |
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67 | |||
68 | |||
69 | else { |
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70 | n = __ieee754_rem_pio2(x,y); |
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71 | switch(n&3) { |
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72 | case 0: return __kernel_cos(y[0],y[1]); |
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73 | case 1: return -__kernel_sin(y[0],y[1],1); |
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74 | case 2: return -__kernel_cos(y[0],y[1]); |
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75 | default: |
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76 | return __kernel_sin(y[0],y[1],1); |
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77 | } |
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78 | } |
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79 | } |
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80 | |||
81 | |||
82 |