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