1 /* origin: FreeBSD /usr/src/lib/msun/src/e_asinf.c */
2 /*
3  * Conversion to float by Ian Lance Taylor, Cygnus Support, [email protected].
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::fabsf::fabsf;
17 use super::sqrt::sqrt;
18 
19 const PIO2: f64 = 1.570796326794896558e+00;
20 
21 /* coefficients for R(x^2) */
22 const P_S0: f32 = 1.6666586697e-01;
23 const P_S1: f32 = -4.2743422091e-02;
24 const P_S2: f32 = -8.6563630030e-03;
25 const Q_S1: f32 = -7.0662963390e-01;
26 
r(z: f32) -> f3227 fn r(z: f32) -> f32 {
28     let p = z * (P_S0 + z * (P_S1 + z * P_S2));
29     let q = 1. + z * Q_S1;
30     p / q
31 }
32 
33 /// Arcsine (f32)
34 ///
35 /// Computes the inverse sine (arc sine) of the argument `x`.
36 /// Arguments to asin must be in the range -1 to 1.
37 /// Returns values in radians, in the range of -pi/2 to pi/2.
38 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
asinf(mut x: f32) -> f3239 pub fn asinf(mut x: f32) -> f32 {
40     let x1p_120 = f64::from_bits(0x3870000000000000); // 0x1p-120 === 2 ^ (-120)
41 
42     let hx = x.to_bits();
43     let ix = hx & 0x7fffffff;
44 
45     if ix >= 0x3f800000 {
46         /* |x| >= 1 */
47         if ix == 0x3f800000 {
48             /* |x| == 1 */
49             return ((x as f64) * PIO2 + x1p_120) as f32; /* asin(+-1) = +-pi/2 with inexact */
50         }
51         return 0. / (x - x); /* asin(|x|>1) is NaN */
52     }
53 
54     if ix < 0x3f000000 {
55         /* |x| < 0.5 */
56         /* if 0x1p-126 <= |x| < 0x1p-12, avoid raising underflow */
57         if (ix < 0x39800000) && (ix >= 0x00800000) {
58             return x;
59         }
60         return x + x * r(x * x);
61     }
62 
63     /* 1 > |x| >= 0.5 */
64     let z = (1. - fabsf(x)) * 0.5;
65     let s = sqrt(z as f64);
66     x = (PIO2 - 2. * (s + s * (r(z) as f64))) as f32;
67     if (hx >> 31) != 0 {
68         -x
69     } else {
70         x
71     }
72 }
73