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 #include <sys/cdefs.h>
14 #if defined(LIBM_SCCS) && !defined(lint)
15 __RCSID("$NetBSD: s_cos.c,v 1.12 2024/05/08 01:40:27 riastradh Exp $");
16 #endif
17
18 /* cos(x)
19 * Return cosine function of x.
20 *
21 * kernel function:
22 * __kernel_sin ... sine function on [-pi/4,pi/4]
23 * __kernel_cos ... cosine function on [-pi/4,pi/4]
24 * __ieee754_rem_pio2 ... argument reduction routine
25 *
26 * Method.
27 * Let S,C and T denote the sin, cos and tan respectively on
28 * [-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
29 * in [-pi/4 , +pi/4], and let n = k mod 4.
30 * We have
31 *
32 * n sin(x) cos(x) tan(x)
33 * ----------------------------------------------------------
34 * 0 S C T
35 * 1 C -S -1/T
36 * 2 -S -C T
37 * 3 -C S -1/T
38 * ----------------------------------------------------------
39 *
40 * Special cases:
41 * Let trig be any of sin, cos, or tan.
42 * trig(+-INF) is NaN, with signals;
43 * trig(NaN) is that NaN;
44 *
45 * Accuracy:
46 * TRIG(x) returns trig(x) nearly rounded
47 */
48
49 #include "namespace.h"
50 #include "math.h"
51 #include "math_private.h"
52
__weak_alias(cos,_cos)53 __weak_alias(cos, _cos)
54
55 double
56 cos(double x)
57 {
58 double y[2],z=0.0;
59 int32_t n, ix;
60
61 /* High word of x. */
62 GET_HIGH_WORD(ix,x);
63
64 /* |x| ~< pi/4 */
65 ix &= 0x7fffffff;
66 if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
67
68 /* cos(Inf or NaN) is NaN */
69 else if (ix>=0x7ff00000) return x-x;
70
71 /* argument reduction needed */
72 else {
73 n = __ieee754_rem_pio2(x,y);
74 switch(n&3) {
75 case 0: return __kernel_cos(y[0],y[1]);
76 case 1: return -__kernel_sin(y[0],y[1],1);
77 case 2: return -__kernel_cos(y[0],y[1]);
78 default:
79 return __kernel_sin(y[0],y[1],1);
80 }
81 }
82 }
83