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---
s_cos.c (2068B)
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1 /* @(#)s_cos.c 5.1 93/09/24 */
2 /*
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
5 *
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
9 * is preserved.
10 * ====================================================
11 */
12
13 #ifndef lint
14 static char rcsid[] = "$FreeBSD: src/lib/msun/src/s_cos.c,v 1.9 2003/07/23 04:53:46 peter Exp $";
15 #endif
16
17 /* cos(x)
18 * Return cosine function of x.
19 *
20 * kernel function:
21 * __kernel_sin ... sine function on [-pi/4,pi/4]
22 * __kernel_cos ... cosine function on [-pi/4,pi/4]
23 * __ieee754_rem_pio2 ... argument reduction routine
24 *
25 * Method.
26 * Let S,C and T denote the sin, cos and tan respectively on
27 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
28 * in [-pi/4 , +pi/4], and let n = k mod 4.
29 * We have
30 *
31 * n sin(x) cos(x) tan(x)
32 * ----------------------------------------------------------
33 * 0 S C T
34 * 1 C -S -1/T
35 * 2 -S -C T
36 * 3 -C S -1/T
37 * ----------------------------------------------------------
38 *
39 * Special cases:
40 * Let trig be any of sin, cos, or tan.
41 * trig(+-INF) is NaN, with signals;
42 * trig(NaN) is that NaN;
43 *
44 * Accuracy:
45 * TRIG(x) returns trig(x) nearly rounded
46 */
47
48 #include "math.h"
49 #include "math_private.h"
50
51 double
52 cos(double x)
53 {
54 double y[2],z=0.0;
55 int32_t n, ix;
56
57 /* High word of x. */
58 GET_HIGH_WORD(ix,x);
59
60 /* |x| ~< pi/4 */
61 ix &= 0x7fffffff;
62 if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
63
64 /* cos(Inf or NaN) is NaN */
65 else if (ix>=0x7ff00000) return x-x;
66
67 /* argument reduction needed */
68 else {
69 n = __ieee754_rem_pio2(x,y);
70 switch(n&3) {
71 case 0: return __kernel_cos(y[0],y[1]);
72 case 1: return -__kernel_sin(y[0],y[1],1);
73 case 2: return -__kernel_cos(y[0],y[1]);
74 default:
75 return __kernel_sin(y[0],y[1],1);
76 }
77 }
78 }