libm/math/
atan2f.rs

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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
16use super::atanf;
17use super::fabsf;
18
19const PI: f32 = 3.1415927410e+00; /* 0x40490fdb */
20const 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)]
28pub 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}
libm/math/atan2f.rs

libm/math/
atan2f.rs
