1
2/* @(#)s_cos.c 1.3 95/01/18 */
3/*
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 *
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
10 * is preserved.
11 * ====================================================
12 */
13
14/* ieee_cos(x)
15 * Return cosine function of x.
16 *
17 * kernel function:
18 *	__kernel_sin		... sine function on [-pi/4,pi/4]
19 *	__kernel_cos		... cosine function on [-pi/4,pi/4]
20 *	__ieee754_rem_pio2	... argument reduction routine
21 *
22 * Method.
23 *      Let S,C and T denote the sin, cos and tan respectively on
24 *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
25 *	in [-pi/4 , +pi/4], and let n = k mod 4.
26 *	We have
27 *
28 *          n        ieee_sin(x)      ieee_cos(x)        ieee_tan(x)
29 *     ----------------------------------------------------------
30 *	    0	       S	   C		 T
31 *	    1	       C	  -S		-1/T
32 *	    2	      -S	  -C		 T
33 *	    3	      -C	   S		-1/T
34 *     ----------------------------------------------------------
35 *
36 * Special cases:
37 *      Let trig be any of sin, cos, or tan.
38 *      trig(+-INF)  is NaN, with signals;
39 *      trig(NaN)    is that NaN;
40 *
41 * Accuracy:
42 *	TRIG(x) returns trig(x) nearly rounded
43 */
44
45#include "fdlibm.h"
46
47#ifdef __STDC__
48	double ieee_cos(double x)
49#else
50	double ieee_cos(x)
51	double x;
52#endif
53{
54	double y[2],z=0.0;
55	int n, ix;
56
57    /* High word of x. */
58	ix = __HI(x);
59
60    /* |x| ~< pi/4 */
61	ix &= 0x7fffffff;
62	if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
63
64    /* ieee_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}
79