1/* origin: FreeBSD /usr/src/lib/msun/src/e_asinf.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::sqrt::sqrt;
17use super::support::Float;
18
19const PIO2: f64 = 1.570796326794896558e+00;
20
21/* coefficients for R(x^2) */
22const P_S0: f32 = 1.6666586697e-01;
23const P_S1: f32 = -4.2743422091e-02;
24const P_S2: f32 = -8.6563630030e-03;
25const Q_S1: f32 = -7.0662963390e-01;
26
27fn r(z: f32) -> f32 {
28 let p: f32 = z * (P_S0 + z * (P_S1 + z * P_S2));
29 let q: f32 = 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)]
39pub 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 (0x00800000..0x39800000).contains(&ix) {
58 return x;
59 }
60 return x + x * r(x * x);
61 }
62
63 /* 1 > |x| >= 0.5 */
64 let z = (1. - Float::abs(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 { -x } else { x }
68}
69