Atlas - s_cos.c
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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
46double 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}
73libm_hidden_def(cos)
74
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