/home/jaouen/pok_official/pok/trunk/libpok/libm/e_atan2f.c

/*
 *                               POK header
 * 
 * The following file is a part of the POK project. Any modification should
 * made according to the POK licence. You CANNOT use this file or a part of
 * this file is this part of a file for your own project
 *
 * For more information on the POK licence, please see our LICENCE FILE
 *
 * Please follow the coding guidelines described in doc/CODING_GUIDELINES
 *
 *                                      Copyright (c) 2007-2009 POK team 
 *
 * Created by julien on Fri Jan 30 14:41:34 2009 
 */

/* e_atan2f.c -- float version of e_atan2.c.
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 */

/*
 * ====================================================
 * 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.
 * ====================================================
 */

#ifdef POK_NEEDS_LIBMATH
#include <libm.h>
#include "math_private.h"

static const float
tiny  = 1.0e-30,
zero  = 0.0,
pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
pi      = 3.1415925026e+00, /* 0x40490fda */
pi_lo   = 1.5099578832e-07; /* 0x34222168 */

float
__ieee754_atan2f(float y, float x)
{
        float z;
        int32_t k,m,hx,hy,ix,iy;

        GET_FLOAT_WORD(hx,x);
        ix = hx&0x7fffffff;
        GET_FLOAT_WORD(hy,y);
        iy = hy&0x7fffffff;
        if((ix>0x7f800000)||
           (iy>0x7f800000))     /* x or y is NaN */
           return x+y;
        if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
        m = ((hy>>31)&1)|((hx>>30)&2);  /* 2*sign(x)+sign(y) */

    /* when y = 0 */
        if(iy==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==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;

    /* when x is INF */
        if(ix==0x7f800000) {
            if(iy==0x7f800000) {
                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  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
                    case 3: return (float)-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==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;

    /* compute y/x */
        k = (iy-ix)>>23;
        if(k > 60) z=pi_o_2+(float)0.5*pi_lo;   /* |y/x| >  2**60 */
        else if(hx<0&&k<-60) z=0.0;     /* |y|/x < -2**60 */
        else z=atanf(fabsf(y/x));       /* safe to do y/x */
        switch (m) {
            case 0: return       z  ;   /* atan(+,+) */
            case 1: {
                      uint32_t zh;
                      GET_FLOAT_WORD(zh,z);
                      SET_FLOAT_WORD(z,zh ^ 0x80000000);
                    }
                    return       z  ;   /* atan(-,+) */
            case 2: return  pi-(z-pi_lo);/* atan(+,-) */
            default: /* case 3 */
                    return  (z-pi_lo)-pi;/* atan(-,-) */
        }
}
#endif