/* @(#)s_cos.c 1.3 95/01/18 */

/*

 * ====================================================

 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.

 *

 * Developed at SunSoft, a Sun Microsystems, Inc. business.

 * Permission to use, copy, modify, and distribute this

 * software is freely granted, provided that this notice 

 * is preserved.

 * ====================================================

 */

/* cos(x)

 * Return cosine function of x.

 *

 * kernel function:

 *	__kernel_sin		... sine function on [-pi/4,pi/4]

 *	__kernel_cos		... cosine function on [-pi/4,pi/4]

 *	__ieee754_rem_pio2	... argument reduction routine

 *

 * Method.

 *      Let S,C and T denote the sin, cos and tan respectively on 

 *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2 

 *	in [-pi/4 , +pi/4], and let n = k mod 4.

 *	We have

 *

 *          n        sin(x)      cos(x)        tan(x)

 *     ----------------------------------------------------------

 *	    0	       S	   C		 T

 *	    1	       C	  -S		-1/T

 *	    2	      -S	  -C		 T

 *	    3	      -C	   S		-1/T

 *     ----------------------------------------------------------

 *

 * Special cases:

 *      Let trig be any of sin, cos, or tan.

 *      trig(+-INF)  is NaN, with signals;

 *      trig(NaN)    is that NaN;

 *

 * Accuracy:

 *	TRIG(x) returns trig(x) nearly rounded 

 */

#include "fdlibm.h"

#ifdef __STDC__

	double cos(double x)

#else

	double cos(x)

	double x;

#endif

{

	double y[2],z=0.0;

	int n, ix;

    /* High word of x. */

	ix = __HI(x);

    /* |x| ~< pi/4 */

	ix &= 0x7fffffff;

	if(ix <= 0x3fe921fb) return __kernel_cos(x,z);

    /* cos(Inf or NaN) is NaN */

	else if (ix>=0x7ff00000) return x-x;

    /* argument reduction needed */

	else {

	    n = __ieee754_rem_pio2(x,y);

	    switch(n&3) {

		case 0: return  __kernel_cos(y[0],y[1]);

		case 1: return -__kernel_sin(y[0],y[1],1);

		case 2: return -__kernel_cos(y[0],y[1]);

		default:

		        return  __kernel_sin(y[0],y[1],1);

	    }

	}

}