xref: /freebsd/lib/msun/src/e_atan2f.c (revision 069ac184)
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 #include <sys/cdefs.h>
17 #include "math.h"
18 #include "math_private.h"
19 
20 static volatile float
21 tiny  = 1.0e-30;
22 static const float
23 zero  = 0.0,
24 pi_o_4  = 7.8539818525e-01, /* 0x3f490fdb */
25 pi_o_2  = 1.5707963705e+00, /* 0x3fc90fdb */
26 pi      = 3.1415927410e+00; /* 0x40490fdb */
27 static volatile float
28 pi_lo   = -8.7422776573e-08; /* 0xb3bbbd2e */
29 
30 float
31 atan2f(float y, float x)
32 {
33 	float z;
34 	int32_t k,m,hx,hy,ix,iy;
35 
36 	GET_FLOAT_WORD(hx,x);
37 	ix = hx&0x7fffffff;
38 	GET_FLOAT_WORD(hy,y);
39 	iy = hy&0x7fffffff;
40 	if((ix>0x7f800000)||
41 	   (iy>0x7f800000))	/* x or y is NaN */
42 	    return nan_mix(x, y);
43 	if(hx==0x3f800000) return atanf(y);   /* x=1.0 */
44 	m = ((hy>>31)&1)|((hx>>30)&2);	/* 2*sign(x)+sign(y) */
45 
46     /* when y = 0 */
47 	if(iy==0) {
48 	    switch(m) {
49 		case 0:
50 		case 1: return y; 	/* atan(+-0,+anything)=+-0 */
51 		case 2: return  pi+tiny;/* atan(+0,-anything) = pi */
52 		case 3: return -pi-tiny;/* atan(-0,-anything) =-pi */
53 	    }
54 	}
55     /* when x = 0 */
56 	if(ix==0) return (hy<0)?  -pi_o_2-tiny: pi_o_2+tiny;
57 
58     /* when x is INF */
59 	if(ix==0x7f800000) {
60 	    if(iy==0x7f800000) {
61 		switch(m) {
62 		    case 0: return  pi_o_4+tiny;/* atan(+INF,+INF) */
63 		    case 1: return -pi_o_4-tiny;/* atan(-INF,+INF) */
64 		    case 2: return  (float)3.0*pi_o_4+tiny;/*atan(+INF,-INF)*/
65 		    case 3: return (float)-3.0*pi_o_4-tiny;/*atan(-INF,-INF)*/
66 		}
67 	    } else {
68 		switch(m) {
69 		    case 0: return  zero  ;	/* atan(+...,+INF) */
70 		    case 1: return -zero  ;	/* atan(-...,+INF) */
71 		    case 2: return  pi+tiny  ;	/* atan(+...,-INF) */
72 		    case 3: return -pi-tiny  ;	/* atan(-...,-INF) */
73 		}
74 	    }
75 	}
76     /* when y is INF */
77 	if(iy==0x7f800000) return (hy<0)? -pi_o_2-tiny: pi_o_2+tiny;
78 
79     /* compute y/x */
80 	k = (iy-ix)>>23;
81 	if(k > 26) {			/* |y/x| >  2**26 */
82 	    z=pi_o_2+(float)0.5*pi_lo;
83 	    m&=1;
84 	}
85 	else if(k<-26&&hx<0) z=0.0; 	/* 0 > |y|/x > -2**-26 */
86 	else z=atanf(fabsf(y/x));	/* safe to do y/x */
87 	switch (m) {
88 	    case 0: return       z  ;	/* atan(+,+) */
89 	    case 1: return      -z  ;	/* atan(-,+) */
90 	    case 2: return  pi-(z-pi_lo);/* atan(+,-) */
91 	    default: /* case 3 */
92 	    	    return  (z-pi_lo)-pi;/* atan(-,-) */
93 	}
94 }
95