libm/upstream-freebsd/lib/msun/src/e_atan2f.c

/* 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 volatile float
tiny  = 1.0e-30;
static const float
zero  = 0.0,
pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
pi      = 3.1415927410e+00; /* 0x40490fdb */
static volatile float
pi_lo   = -8.7422776573e-08; /* 0xb3bbbd2e */

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 nan_mix(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 > 26) {			/* |y/x| >  2**26 */
	    z=pi_o_2+(float)0.5*pi_lo;
	    m&=1;
	}
	else if(k<-26&&hx<0) z=0.0; 	/* 0 > |y|/x > -2**-26 */
	else z=atanf(fabsf(y/x));	/* safe to do y/x */
	switch (m) {
	    case 0: return       z  ;	/* atan(+,+) */
	    case 1: return      -z  ;	/* atan(-,+) */
	    case 2: return  pi-(z-pi_lo);/* atan(+,-) */
	    default: /* case 3 */
	    	    return  (z-pi_lo)-pi;/* atan(-,-) */
	}
}