/* @(#)s_cos.c 5.1 93/09/24 */

/*

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

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

 *

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

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

 * software is freely granted, provided that this notice

 * is preserved.

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

 */

#if defined(LIBM_SCCS) && !defined(lint)

static const char rcsid[] =

    "$NetBSD: s_cos.c,v 1.7 1995/05/10 20:47:02 jtc Exp $";

#endif

/* 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 "math.h"

#include "math_private.h"

libm_hidden_proto(cos)

#ifdef __STDC__

     double cos(double x)

#else

     double cos(x)

     double x;

#endif

{

    double y[2], z = 0.0;

    int32_t n, ix;

    /* High word of x. */

    GET_HIGH_WORD(ix, 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);

        }

    }

}

libm_hidden_def(cos)