1//! Tangent approximation for a single-precision float.
2
3use super::F32;
4
5impl F32 {
6 /// Approximates `tan(x)` in radians with a maximum error of `0.6`.
7 pub fn tan(self) -> Self {
8 self.sin() / self.cos()
9 }
10}
11
12#[cfg(test)]
13mod tests {
14 use super::F32;
15
16 /// Maximum error in radians
17 // TODO(tarcieri): this is kinda bad, find a better approximation?
18 const MAX_ERROR: f32 = 0.6;
19
20 /// Tangent test vectors - `(input, output)`
21 const TEST_VECTORS: &[(f32, f32)] = &[
22 (0.000, 0.000),
23 (0.140, 0.141),
24 (0.279, 0.287),
25 (0.419, 0.445),
26 (0.559, 0.625),
27 (0.698, 0.839),
28 (0.838, 1.111),
29 (0.977, 1.483),
30 (1.117, 2.050),
31 (1.257, 3.078),
32 (1.396, 5.671),
33 (1.536, 28.636),
34 (1.676, -9.514),
35 (1.815, -4.011),
36 (1.955, -2.475),
37 (2.094, -1.732),
38 (2.234, -1.280),
39 (2.374, -0.966),
40 (2.513, -0.727),
41 (2.653, -0.532),
42 (2.793, -0.364),
43 (2.932, -0.213),
44 (3.072, -0.070),
45 (3.211, 0.070),
46 (3.351, 0.213),
47 (3.491, 0.364),
48 (3.630, 0.532),
49 (3.770, 0.727),
50 (3.910, 0.966),
51 (4.049, 1.280),
52 (4.189, 1.732),
53 (4.328, 2.475),
54 (4.468, 4.011),
55 (4.608, 9.514),
56 (4.747, -28.636),
57 (4.887, -5.671),
58 (5.027, -3.078),
59 (5.166, -2.050),
60 (5.306, -1.483),
61 (5.445, -1.111),
62 (5.585, -0.839),
63 (5.725, -0.625),
64 (5.864, -0.445),
65 (6.004, -0.287),
66 (6.144, -0.141),
67 (6.283, 0.000),
68 ];
69
70 #[test]
71 fn sanity_check() {
72 for &(x, expected) in TEST_VECTORS {
73 let tan_x = F32(x).tan();
74 let delta = (tan_x - expected).abs();
75
76 assert!(
77 delta <= MAX_ERROR,
78 "delta {} too large: {} vs {}",
79 delta,
80 tan_x,
81 expected
82 );
83 }
84 }
85
86 #[test]
87 fn zero() {
88 assert_eq!(F32::ZERO.tan(), F32::ZERO);
89 }
90
91 #[test]
92 fn nan() {
93 assert!(F32::NAN.tan().is_nan());
94 }
95}
96