e_atan2f.c revision 22993 
1/* e_atan2f.c -- float version of e_atan2.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@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#ifndef lint
17static char rcsid[] = "$Id$";
18#endif
19
20#include "math.h"
21#include "math_private.h"
22
23#ifdef __STDC__
24static const float
25#else
26static float
27#endif
28tiny  = 1.0e-30,
29zero  = 0.0,
30pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
31pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
32pi      = 3.1415925026e+00, /* 0x40490fda */
33pi_lo   = 1.5099578832e-07; /* 0x34222168 */
34
35#ifdef __STDC__
36	float __ieee754_atan2f(float y, float x)
37#else
38	float __ieee754_atan2f(y,x)
39	float  y,x;
40#endif
41{
42	float z;
43	int32_t k,m,hx,hy,ix,iy;
44
45	GET_FLOAT_WORD(hx,x);
46	ix = hx&0x7fffffff;
47	GET_FLOAT_WORD(hy,y);
48	iy = hy&0x7fffffff;
49	if((ix>0x7f800000)||
50	   (iy>0x7f800000))	/* x or y is NaN */
51	   return x+y;
52	if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
53	m = ((hy>>31)&1)|((hx>>30)&2);	/* 2*sign(x)+sign(y) */
54
55    /* when y = 0 */
56	if(iy==0) {
57	    switch(m) {
58		case 0:
59		case 1: return y; 	/* atan(+-0,+anything)=+-0 */
60		case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
61		case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
62	    }
63	}
64    /* when x = 0 */
65	if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
66
67    /* when x is INF */
68	if(ix==0x7f800000) {
69	    if(iy==0x7f800000) {
70		switch(m) {
71		    case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
72		    case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
73		    case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
74		    case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
75		}
76	    } else {
77		switch(m) {
78		    case 0: return  zero  ;	/* atan(+...,+INF) */
79		    case 1: return -zero  ;	/* atan(-...,+INF) */
80		    case 2: return  pi+tiny  ;	/* atan(+...,-INF) */
81		    case 3: return -pi-tiny  ;	/* atan(-...,-INF) */
82		}
83	    }
84	}
85    /* when y is INF */
86	if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
87
88    /* compute y/x */
89	k = (iy-ix)>>23;
90	if(k > 60) z=pi_o_2+(float)0.5*pi_lo; 	/* |y/x| >  2**60 */
91	else if(hx<0&&k<-60) z=0.0; 	/* |y|/x < -2**60 */
92	else z=atanf(fabsf(y/x));	/* safe to do y/x */
93	switch (m) {
94	    case 0: return       z  ;	/* atan(+,+) */
95	    case 1: {
96	    	      u_int32_t zh;
97		      GET_FLOAT_WORD(zh,z);
98		      SET_FLOAT_WORD(z,zh ^ 0x80000000);
99		    }
100		    return       z  ;	/* atan(-,+) */
101	    case 2: return  pi-(z-pi_lo);/* atan(+,-) */
102	    default: /* case 3 */
103	    	    return  (z-pi_lo)-pi;/* atan(-,-) */
104	}
105}
106