e_atan2f.c

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

#include "math.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
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: {
                  u_int32_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(-,-) */
    }
}