Subversion Repositories or1k

/* @(#)s_tan.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 char rcsid[] = "$NetBSD: s_tan.c,v 1.7 1995/05/10 20:48:18 jtc Exp $";

#endif

/* tan(x)

 * Return tangent function of x.

 *

 * kernel function:

 *      __kernel_tan            ... tangent 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"

#ifdef __STDC__

        double tan(double x)

#else

        double tan(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_tan(x,z,1);

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

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

    /* argument reduction needed */

        else {

            n = __ieee754_rem_pio2(x,y);

            return __kernel_tan(y[0],y[1],1-((n&1)<<1)); /*   1 -- n even

                                                        -1 -- n odd */

        }

}