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 atan(mut x: f32) -> f32 {
17 const ATAN_HI: [f32; 4] = [
18 4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
19 7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
20 9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
21 1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
22 ];
23
24 const ATAN_LO: [f32; 4] = [
25 5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
26 3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
27 3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
28 7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
29 ];
30
31 const A_T: [f32; 5] =
32 [3.3333328366e-01, -1.9999158382e-01, 1.4253635705e-01, -1.0648017377e-01, 6.1687607318e-02];
33 let x1p_120 = f32::from_bits(0x03800000); // 0x1p-120 === 2 ^ (-120)
34
35 let z: f32;
36
37 let mut ix = x.to_bits();
38 let sign = (ix >> 31) != 0;
39 ix &= 0x7fffffff;
40
41 if ix >= 0x4c800000 {
42 /* if |x| >= 2**26 */
43 if x.is_nan() {
44 return x;
45 }
46 z = ATAN_HI[3] + x1p_120;
47 return if sign {
48 -z
49 } else {
50 z
51 };
52 }
53 let id = if ix < 0x3ee00000 {
54 /* |x| < 0.4375 */
55 if ix < 0x39800000 {
56 return x;
57 }
58 -1
59 } else {
60 x = super::abs(x);
61 if ix < 0x3f980000 {
62 /* |x| < 1.1875 */
63 if ix < 0x3f300000 {
64 /* 7/16 <= |x| < 11/16 */
65 x = (2. * x - 1.) / (2. + x);
66 0
67 } else {
68 /* 11/16 <= |x| < 19/16 */
69 x = (x - 1.) / (x + 1.);
70 1
71 }
72 } else if ix < 0x401c0000 {
73 /* |x| < 2.4375 */
74 x = (x - 1.5) / (1. + 1.5 * x);
75 2
76 } else {
77 /* 2.4375 <= |x| < 2**26 */
78 x = -1. / x;
79 3
80 }
81 };
82 /* end of argument reduction */
83 z = x * x;
84 let w = z * z;
85 /* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
86 let s1 = z * (A_T[0] + w * (A_T[2] + w * A_T[4]));
87 let s2 = w * (A_T[1] + w * A_T[3]);
88 if id < 0 {
89 return x - x * (s1 + s2);
90 }
91 let id = id as usize;
92 let z = ATAN_HI[id] - ((x * (s1 + s2) - ATAN_LO[id]) - x);
93 if sign {
94 -z
95 } else {
96 z
97 }
98}
99