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      1 /* e_atan2f.c -- float version of e_atan2.c.
      2  * Conversion to float by Ian Lance Taylor, Cygnus Support, ian (at) cygnus.com.
      3  */
      4 
      5 /*
      6  * ====================================================
      7  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
      8  *
      9  * Developed at SunPro, a Sun Microsystems, Inc. business.
     10  * Permission to use, copy, modify, and distribute this
     11  * software is freely granted, provided that this notice
     12  * is preserved.
     13  * ====================================================
     14  */
     15 
     16 #include <sys/cdefs.h>
     17 #if defined(LIBM_SCCS) && !defined(lint)
     18 __RCSID("$NetBSD: e_atan2f.c,v 1.7 2002/05/26 22:01:49 wiz Exp $");
     19 #endif
     20 
     21 #include "math.h"
     22 #include "math_private.h"
     23 
     24 static const float
     25 tiny  = 1.0e-30,
     26 zero  = 0.0,
     27 pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
     28 pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
     29 pi      = 3.1415925026e+00, /* 0x40490fda */
     30 pi_lo   = 1.5099578832e-07; /* 0x34222168 */
     31 
     32 float
     33 __ieee754_atan2f(float y, float x)
     34 {
     35 	float z;
     36 	int32_t k,m,hx,hy,ix,iy;
     37 
     38 	GET_FLOAT_WORD(hx,x);
     39 	ix = hx&0x7fffffff;
     40 	GET_FLOAT_WORD(hy,y);
     41 	iy = hy&0x7fffffff;
     42 	if((ix>0x7f800000)||
     43 	   (iy>0x7f800000))	/* x or y is NaN */
     44 	   return x+y;
     45 	if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
     46 	m = ((hy>>31)&1)|((hx>>30)&2);	/* 2*sign(x)+sign(y) */
     47 
     48     /* when y = 0 */
     49 	if(iy==0) {
     50 	    switch(m) {
     51 		case 0:
     52 		case 1: return y; 	/* atan(+-0,+anything)=+-0 */
     53 		case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
     54 		case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
     55 	    }
     56 	}
     57     /* when x = 0 */
     58 	if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
     59 
     60     /* when x is INF */
     61 	if(ix==0x7f800000) {
     62 	    if(iy==0x7f800000) {
     63 		switch(m) {
     64 		    case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
     65 		    case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
     66 		    case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
     67 		    case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
     68 		}
     69 	    } else {
     70 		switch(m) {
     71 		    case 0: return  zero  ;	/* atan(+...,+INF) */
     72 		    case 1: return -zero  ;	/* atan(-...,+INF) */
     73 		    case 2: return  pi+tiny  ;	/* atan(+...,-INF) */
     74 		    case 3: return -pi-tiny  ;	/* atan(-...,-INF) */
     75 		}
     76 	    }
     77 	}
     78     /* when y is INF */
     79 	if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
     80 
     81     /* compute y/x */
     82 	k = (iy-ix)>>23;
     83 	if(k > 60) z=pi_o_2+(float)0.5*pi_lo; 	/* |y/x| >  2**60 */
     84 	else if(hx<0&&k<-60) z=0.0; 	/* |y|/x < -2**60 */
     85 	else z=atanf(fabsf(y/x));	/* safe to do y/x */
     86 	switch (m) {
     87 	    case 0: return       z  ;	/* atan(+,+) */
     88 	    case 1: {
     89 	    	      u_int32_t zh;
     90 		      GET_FLOAT_WORD(zh,z);
     91 		      SET_FLOAT_WORD(z,zh ^ 0x80000000);
     92 		    }
     93 		    return       z  ;	/* atan(-,+) */
     94 	    case 2: return  pi-(z-pi_lo);/* atan(+,-) */
     95 	    default: /* case 3 */
     96 	    	    return  (z-pi_lo)-pi;/* atan(-,-) */
     97 	}
     98 }
     99