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 use super::atanf;
17 use super::fabsf;
18
19 const PI: f32 = 3.1415927410e+00; /* 0x40490fdb */
20 const PI_LO: f32 = -8.7422776573e-08; /* 0xb3bbbd2e */
21
22 /// Arctangent of y/x (f32)
23 ///
24 /// Computes the inverse tangent (arc tangent) of `y/x`.
25 /// Produces the correct result even for angles near pi/2 or -pi/2 (that is, when `x` is near 0).
26 /// Returns a value in radians, in the range of -pi to pi.
27 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
atan2f(y: f32, x: f32) -> f3228 pub fn atan2f(y: f32, x: f32) -> f32 {
29 if x.is_nan() || y.is_nan() {
30 return x + y;
31 }
32 let mut ix = x.to_bits();
33 let mut iy = y.to_bits();
34
35 if ix == 0x3f800000 {
36 /* x=1.0 */
37 return atanf(y);
38 }
39 let m = ((iy >> 31) & 1) | ((ix >> 30) & 2); /* 2*sign(x)+sign(y) */
40 ix &= 0x7fffffff;
41 iy &= 0x7fffffff;
42
43 /* when y = 0 */
44 if iy == 0 {
45 return match m {
46 0 | 1 => y, /* atan(+-0,+anything)=+-0 */
47 2 => PI, /* atan(+0,-anything) = pi */
48 3 | _ => -PI, /* atan(-0,-anything) =-pi */
49 };
50 }
51 /* when x = 0 */
52 if ix == 0 {
53 return if m & 1 != 0 { -PI / 2. } else { PI / 2. };
54 }
55 /* when x is INF */
56 if ix == 0x7f800000 {
57 return if iy == 0x7f800000 {
58 match m {
59 0 => PI / 4., /* atan(+INF,+INF) */
60 1 => -PI / 4., /* atan(-INF,+INF) */
61 2 => 3. * PI / 4., /* atan(+INF,-INF)*/
62 3 | _ => -3. * PI / 4., /* atan(-INF,-INF)*/
63 }
64 } else {
65 match m {
66 0 => 0., /* atan(+...,+INF) */
67 1 => -0., /* atan(-...,+INF) */
68 2 => PI, /* atan(+...,-INF) */
69 3 | _ => -PI, /* atan(-...,-INF) */
70 }
71 };
72 }
73 /* |y/x| > 0x1p26 */
74 if (ix + (26 << 23) < iy) || (iy == 0x7f800000) {
75 return if m & 1 != 0 { -PI / 2. } else { PI / 2. };
76 }
77
78 /* z = atan(|y/x|) with correct underflow */
79 let z = if (m & 2 != 0) && (iy + (26 << 23) < ix) {
80 /*|y/x| < 0x1p-26, x < 0 */
81 0.
82 } else {
83 atanf(fabsf(y / x))
84 };
85 match m {
86 0 => z, /* atan(+,+) */
87 1 => -z, /* atan(-,+) */
88 2 => PI - (z - PI_LO), /* atan(+,-) */
89 _ => (z - PI_LO) - PI, /* case 3 */ /* atan(-,-) */
90 }
91 }
92