ps_ecc/polynomial/methods/
first_n_coefficients.rs

1use crate::{polynomial::constants::POLYNOMIAL_MAX_COEFFICIENTS, Polynomial};
2
3impl Polynomial {
4    /// Returns the first `n` coefficients.
5    ///
6    /// The returned slice has length `min(n, 255)`.
7    #[must_use]
8    pub fn first_n_coefficients(&self, n: usize) -> &[u8] {
9        &self.coefficients[..n.min(POLYNOMIAL_MAX_COEFFICIENTS)]
10    }
11}
12
13#[cfg(test)]
14mod tests {
15    use crate::Polynomial;
16
17    #[test]
18    fn exact_size() {
19        let mut p = Polynomial::default();
20
21        p.set(0, 1);
22        p.set(1, 2);
23        p.set(2, 3);
24
25        assert_eq!(p.first_n_coefficients(3), &[1, 2, 3]);
26    }
27
28    #[test]
29    fn zeros_beyond_degree() {
30        let mut p = Polynomial::default();
31
32        p.set(0, 1);
33        p.set(1, 2);
34
35        assert_eq!(p.first_n_coefficients(5), &[1, 2, 0, 0, 0]);
36    }
37
38    #[test]
39    fn truncates() {
40        let mut p = Polynomial::default();
41
42        p.set(0, 1);
43        p.set(1, 2);
44        p.set(2, 3);
45        p.set(3, 4);
46        p.set(4, 5);
47
48        assert_eq!(p.first_n_coefficients(3), &[1, 2, 3]);
49    }
50
51    #[test]
52    fn zero_polynomial() {
53        let p = Polynomial::default();
54
55        assert_eq!(p.first_n_coefficients(3), &[0, 0, 0]);
56    }
57
58    #[test]
59    fn n_is_zero() {
60        let mut p = Polynomial::default();
61
62        p.set(0, 1);
63
64        assert_eq!(p.first_n_coefficients(0), &[]);
65    }
66
67    #[test]
68    fn n_is_255() {
69        let mut p = Polynomial::default();
70
71        p.set(0, 1);
72
73        let result = p.first_n_coefficients(255);
74
75        assert_eq!(result.len(), 255);
76        assert_eq!(result[0], 1);
77        assert!(result[1..].iter().all(|&x| x == 0));
78    }
79
80    #[test]
81    fn n_exceeds_255_clamps() {
82        let mut p = Polynomial::default();
83
84        p.set(0, 1);
85        p.set(1, 2);
86
87        let result = p.first_n_coefficients(300);
88
89        assert_eq!(result.len(), 255);
90    }
91}
ps_ecc/polynomial/methods/first_n_coefficients.rs

ps_ecc/polynomial/methods/
first_n_coefficients.rs
