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 <float.h>
44
45#include "math.h"
46#define INLINE_REM_PIO2
47#include "math_private.h"
48#include "e_rem_pio2.c"
49
50double
51cos(double x)
52{
53	double y[2],z=0.0;
54	int32_t n, ix;
55
56    /* High word of x. */
57	GET_HIGH_WORD(ix,x);
58
59    /* |x| ~< pi/4 */
60	ix &= 0x7fffffff;
61	if(ix <= 0x3fe921fb) {
62	    if(ix<0x3e46a09e)			/* if x < 2**-27 * sqrt(2) */
63		if(((int)x)==0) return 1.0;	/* generate inexact */
64	    return __kernel_cos(x,z);
65	}
66
67    /* cos(Inf or NaN) is NaN */
68	else if (ix>=0x7ff00000) return x-x;
69
70    /* argument reduction needed */
71	else {
72	    n = __ieee754_rem_pio2(x,y);
73	    switch(n&3) {
74		case 0: return  __kernel_cos(y[0],y[1]);
75		case 1: return -__kernel_sin(y[0],y[1],1);
76		case 2: return -__kernel_cos(y[0],y[1]);
77		default:
78		        return  __kernel_sin(y[0],y[1],1);
79	    }
80	}
81}
82
83#if (LDBL_MANT_DIG == 53)
84__weak_reference(cos, cosl);
85#endif
86