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annotate src/libm/s_cos.c @ 2756:a98604b691c8

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Expanded the libm support and put it into a separate directory.
author Sam Lantinga <slouken@libsdl.org>
date Mon, 15 Sep 2008 06:33:23 +0000
parents
children dc1eb82ffdaa
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2756
a98604b691c8 Expanded the libm support and put it into a separate directory.
Sam Lantinga <slouken@libsdl.org>
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1 /* @(#)s_cos.c 5.1 93/09/24 */
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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
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13 #if defined(LIBM_SCCS) && !defined(lint)
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14 static char rcsid[] = "$NetBSD: s_cos.c,v 1.7 1995/05/10 20:47:02 jtc Exp $";
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15 #endif
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16
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17 /* cos(x)
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18 * Return cosine function of x.
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19 *
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20 * kernel function:
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21 * __kernel_sin ... sine function on [-pi/4,pi/4]
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22 * __kernel_cos ... cosine function on [-pi/4,pi/4]
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23 * __ieee754_rem_pio2 ... argument reduction routine
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24 *
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25 * Method.
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26 * Let S,C and T denote the sin, cos and tan respectively on
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27 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
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28 * in [-pi/4 , +pi/4], and let n = k mod 4.
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29 * We have
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30 *
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31 * n sin(x) cos(x) tan(x)
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32 * ----------------------------------------------------------
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33 * 0 S C T
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34 * 1 C -S -1/T
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35 * 2 -S -C T
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36 * 3 -C S -1/T
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37 * ----------------------------------------------------------
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38 *
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39 * Special cases:
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40 * Let trig be any of sin, cos, or tan.
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41 * trig(+-INF) is NaN, with signals;
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42 * trig(NaN) is that NaN;
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43 *
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44 * Accuracy:
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45 * TRIG(x) returns trig(x) nearly rounded
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46 */
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47
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48 #include "math.h"
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49 #include "math_private.h"
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50
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51 libm_hidden_proto(cos)
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52 #ifdef __STDC__
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53 double cos(double x)
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54 #else
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55 double cos(x)
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56 double x;
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57 #endif
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58 {
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59 double y[2], z = 0.0;
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60 int32_t n, ix;
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61
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62 /* High word of x. */
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63 GET_HIGH_WORD(ix, x);
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64
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65 /* |x| ~< pi/4 */
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66 ix &= 0x7fffffff;
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67 if (ix <= 0x3fe921fb)
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68 return __kernel_cos(x, z);
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69
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70 /* cos(Inf or NaN) is NaN */
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71 else if (ix >= 0x7ff00000)
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72 return x - x;
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73
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74 /* argument reduction needed */
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75 else {
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76 n = __ieee754_rem_pio2(x, y);
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77 switch (n & 3) {
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78 case 0:
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79 return __kernel_cos(y[0], y[1]);
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80 case 1:
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81 return -__kernel_sin(y[0], y[1], 1);
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82 case 2:
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83 return -__kernel_cos(y[0], y[1]);
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84 default:
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85 return __kernel_sin(y[0], y[1], 1);
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86 }
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87 }
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88 }
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89
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90 libm_hidden_def(cos)