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//===========================================================================

//

//      e_atan2.c

//

//      Part of the standard mathematical function library

//

//===========================================================================

//####ECOSGPLCOPYRIGHTBEGIN####

// -------------------------------------------

// This file is part of eCos, the Embedded Configurable Operating System.

// Copyright (C) 1998, 1999, 2000, 2001, 2002 Red Hat, Inc.

//

// eCos is free software; you can redistribute it and/or modify it under

// the terms of the GNU General Public License as published by the Free

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// FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

// for more details.

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// 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.

//

// As a special exception, if other files instantiate templates or use macros

// or inline functions from this file, or you compile this file and link it

// with other works to produce a work based on this file, this file does not

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//####ECOSGPLCOPYRIGHTEND####

//===========================================================================

//#####DESCRIPTIONBEGIN####

//

// Author(s):   jlarmour

// Contributors:  jlarmour

// Date:        1998-02-13

// Purpose:     

// Description: 

// Usage:       

//

//####DESCRIPTIONEND####

//

//===========================================================================

// CONFIGURATION

#include <pkgconf/libm.h>   // Configuration header

// Include the Math library?

#ifdef CYGPKG_LIBM     

// Derived from code with the following copyright

/* @(#)e_atan2.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.

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

 *

 */

/* __ieee754_atan2(y,x)

 * Method :

 *      1. Reduce y to positive by atan2(y,x)=-atan2(-y,x).

 *      2. Reduce x to positive by (if x and y are unexceptional):

 *              ARG (x+iy) = arctan(y/x)           ... if x > 0,

 *              ARG (x+iy) = pi - arctan[y/(-x)]   ... if x < 0,

 *

 * Special cases:

 *

 *      ATAN2((anything), NaN ) is NaN;

 *      ATAN2(NAN , (anything) ) is NaN;

 *      ATAN2(+-0, +(anything but NaN)) is +-0  ;

 *      ATAN2(+-0, -(anything but NaN)) is +-pi ;

 *      ATAN2(+-(anything but 0 and NaN), 0) is +-pi/2;

 *      ATAN2(+-(anything but INF and NaN), +INF) is +-0 ;

 *      ATAN2(+-(anything but INF and NaN), -INF) is +-pi;

 *      ATAN2(+-INF,+INF ) is +-pi/4 ;

 *      ATAN2(+-INF,-INF ) is +-3pi/4;

 *      ATAN2(+-INF, (anything but,0,NaN, and INF)) is +-pi/2;

 *

 * Constants:

 * The hexadecimal values are the intended ones for the following

 * constants. The decimal values may be used, provided that the

 * compiler will convert from decimal to binary accurately enough

 * to produce the hexadecimal values shown.

 */

#include "mathincl/fdlibm.h"

static const double

tiny  = 1.0e-300,

zero  = 0.0,

pi_o_4  = 7.8539816339744827900E-01, /* 0x3FE921FB, 0x54442D18 */

pi_o_2  = 1.5707963267948965580E+00, /* 0x3FF921FB, 0x54442D18 */

pi      = 3.1415926535897931160E+00, /* 0x400921FB, 0x54442D18 */

pi_lo   = 1.2246467991473531772E-16; /* 0x3CA1A626, 0x33145C07 */

        double __ieee754_atan2(double y, double x)

{

        double z;

        int k,m,hx,hy,ix,iy;

        unsigned lx,ly;

        hx = CYG_LIBM_HI(x); ix = hx&0x7fffffff;

        lx = CYG_LIBM_LO(x);

        hy = CYG_LIBM_HI(y); iy = hy&0x7fffffff;

        ly = CYG_LIBM_LO(y);

        if(((ix|((lx|-lx)>>31))>0x7ff00000)||

           ((iy|((ly|-ly)>>31))>0x7ff00000))    /* x or y is NaN */

           return x+y;

        if(((hx-0x3ff00000)|lx)==0) return atan(y);   /* x=1.0 */

        m = ((hy>>31)&1)|((hx>>30)&2);  /* 2*sign(x)+sign(y) */

    /* when y = 0 */

        if((iy|ly)==0) {

            switch(m) {

                case 0:

                case 1: return y;       /* atan(+-0,+anything)=+-0 */

                case 2: return  pi+tiny;/* atan(+0,-anything) = pi */

                case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */

            }

        }

    /* when x = 0 */

        if((ix|lx)==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;

    /* when x is INF */

        if(ix==0x7ff00000) {

            if(iy==0x7ff00000) {

                switch(m) {

                    case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */

                    case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */

                    case 2: return  3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/

                    case 3: return -3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/

                }

            } else {

                switch(m) {

                    case 0: return  zero  ;     /* atan(+...,+INF) */

                    case 1: return -zero  ;     /* atan(-...,+INF) */

                    case 2: return  pi+tiny  ;  /* atan(+...,-INF) */

                    case 3: return -pi-tiny  ;  /* atan(-...,-INF) */

                }

            }

        }

    /* when y is INF */

        if(iy==0x7ff00000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;

    /* compute y/x */

        k = (iy-ix)>>20;

        if(k > 60) z=pi_o_2+0.5*pi_lo;  /* |y/x| >  2**60 */

        else if(hx<0&&k<-60) z=0.0;     /* |y|/x < -2**60 */

        else z=atan(fabs(y/x));         /* safe to do y/x */

        switch (m) {

            case 0: return       z  ;   /* atan(+,+) */

            case 1: CYG_LIBM_HI(z) ^= 0x80000000;

                    return       z  ;   /* atan(-,+) */

            case 2: return  pi-(z-pi_lo);/* atan(+,-) */

            default: /* case 3 */

                    return  (z-pi_lo)-pi;/* atan(-,-) */

        }

}

#endif // ifdef CYGPKG_LIBM     

// EOF e_atan2.c