1/* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */
2/*
3 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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 "libm.h"
17
18static const float
19pi = 3.1415927410e+00, /* 0x40490fdb */
20pi_lo = -8.7422776573e-08; /* 0xb3bbbd2e */
21
22float atan2f(float y, float x)
23{
24 float z;
25 uint32_t m,ix,iy;
26
27 if (isnan(x) || isnan(y))
28 return x+y;
29 GET_FLOAT_WORD(ix, x);
30 GET_FLOAT_WORD(iy, y);
31 if (ix == 0x3f800000) /* x=1.0 */
32 return atanf(y);
33 m = ((iy>>31)&1) | ((ix>>30)&2); /* 2*sign(x)+sign(y) */
34 ix &= 0x7fffffff;
35 iy &= 0x7fffffff;
36
37 /* when y = 0 */
38 if (iy == 0) {
39 switch (m) {
40 case 0:
41 case 1: return y; /* atan(+-0,+anything)=+-0 */
42 case 2: return pi; /* atan(+0,-anything) = pi */
43 case 3: return -pi; /* atan(-0,-anything) =-pi */
44 }
45 }
46 /* when x = 0 */
47 if (ix == 0)
48 return m&1 ? -pi/2 : pi/2;
49 /* when x is INF */
50 if (ix == 0x7f800000) {
51 if (iy == 0x7f800000) {
52 switch (m) {
53 case 0: return pi/4; /* atan(+INF,+INF) */
54 case 1: return -pi/4; /* atan(-INF,+INF) */
55 case 2: return 3*pi/4; /*atan(+INF,-INF)*/
56 case 3: return -3*pi/4; /*atan(-INF,-INF)*/
57 }
58 } else {
59 switch (m) {
60 case 0: return 0.0f; /* atan(+...,+INF) */
61 case 1: return -0.0f; /* atan(-...,+INF) */
62 case 2: return pi; /* atan(+...,-INF) */
63 case 3: return -pi; /* atan(-...,-INF) */
64 }
65 }
66 }
67 /* |y/x| > 0x1p26 */
68 if (ix+(26<<23) < iy || iy == 0x7f800000)
69 return m&1 ? -pi/2 : pi/2;
70
71 /* z = atan(|y/x|) with correct underflow */
72 if ((m&2) && iy+(26<<23) < ix) /*|y/x| < 0x1p-26, x < 0 */
73 z = 0.0;
74 else
75 z = atanf(fabsf(y/x));
76 switch (m) {
77 case 0: return z; /* atan(+,+) */
78 case 1: return -z; /* atan(-,+) */
79 case 2: return pi - (z-pi_lo); /* atan(+,-) */
80 default: /* case 3 */
81 return (z-pi_lo) - pi; /* atan(-,-) */
82 }
83}