1/*
2 * origin: FreeBSD /usr/src/lib/msun/src/s_atanf.c
3 *
4 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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/// The arctangent function.
16pub fn atan2f(y: f32, x: f32) -> f32 {
17 const PI: f32 = 3.1415927410e+00; /* 0x40490fdb */
18 const PI_LO: f32 = -8.7422776573e-08; /* 0xb3bbbd2e */
19
20 if x.is_nan() || y.is_nan() {
21 return x + y;
22 }
23 let mut ix = x.to_bits();
24 let mut iy = y.to_bits();
25
26 if ix == 0x3f800000 {
27 /* x=1.0 */
28 return super::atan(y);
29 }
30 let m = ((iy >> 31) & 1) | ((ix >> 30) & 2); /* 2*sign(x)+sign(y) */
31 ix &= 0x7fffffff;
32 iy &= 0x7fffffff;
33
34 /* when y = 0 */
35 if iy == 0 {
36 return match m {
37 0 | 1 => y, /* atan(+-0,+anything)=+-0 */
38 2 => PI, /* atan(+0,-anything) = pi */
39 3 | _ => -PI, /* atan(-0,-anything) =-pi */
40 };
41 }
42 /* when x = 0 */
43 if ix == 0 {
44 return if m & 1 != 0 {
45 -PI / 2.
46 } else {
47 PI / 2.
48 };
49 }
50 /* when x is INF */
51 if ix == 0x7f800000 {
52 return if iy == 0x7f800000 {
53 match m {
54 0 => PI / 4., /* atan(+INF,+INF) */
55 1 => -PI / 4., /* atan(-INF,+INF) */
56 2 => 3. * PI / 4., /* atan(+INF,-INF)*/
57 3 | _ => -3. * PI / 4., /* atan(-INF,-INF)*/
58 }
59 } else {
60 match m {
61 0 => 0., /* atan(+...,+INF) */
62 1 => -0., /* atan(-...,+INF) */
63 2 => PI, /* atan(+...,-INF) */
64 3 | _ => -PI, /* atan(-...,-INF) */
65 }
66 };
67 }
68 /* |y/x| > 0x1p26 */
69 if (ix + (26 << 23) < iy) || (iy == 0x7f800000) {
70 return if m & 1 != 0 {
71 -PI / 2.
72 } else {
73 PI / 2.
74 };
75 }
76
77 /* z = atan(|y/x|) with correct underflow */
78 let z = if (m & 2 != 0) && (iy + (26 << 23) < ix) {
79 /*|y/x| < 0x1p-26, x < 0 */
80 0.
81 } else {
82 super::atan(super::abs(y / x))
83 };
84 match m {
85 0 => z, /* atan(+,+) */
86 1 => -z, /* atan(-,+) */
87 2 => PI - (z - PI_LO), /* atan(+,-) */
88 _ => (z - PI_LO) - PI, /* case 3 */ /* atan(-,-) */
89 }
90}
91
92pub fn atan2(x: f32, y: f32) -> f32 {
93 use core::f32::consts::PI;
94 const PI_2: f32 = PI / 2.0;
95 const M_PI_2: f32 = -PI / 2.0;
96 const PI_4: f32 = PI / 4.0;
97 const PI_3_4: f32 = PI_4 * 3.0;
98 let mut r;
99 let c;
100 let abs_y = super::abs(y);
101 if x == 0.0 {
102 if y > 0.0 {
103 return PI_2;
104 }
105 if y == 0.0 {
106 return 0.0;
107 }
108 return M_PI_2;
109 } else if x > 0.0 {
110 r = (x - abs_y) / (x + abs_y);
111 c = PI_4;
112 } else {
113 r = (x + abs_y) / (abs_y - x);
114 c = PI_3_4;
115 }
116 r = 0.1963 * r * r * r - 0.9817 * r + c;
117 return super::copysign(r, y);
118}
119