src/coefficients.rs@ac84e995e119 (annotated)
src/coefficients.rs
Sat, 22 Oct 2022 22:28:04 +0300
- author
- Tuomo Valkonen <tuomov@iki.fi>
- date
- Sat, 22 Oct 2022 22:28:04 +0300
- changeset 2
- ac84e995e119
- parent 0
- 9f27689eb130
- child 5
- 59dc4c5883f4
- permissions
- -rw-r--r--
Convert iteration utilities to GATs
| 0 | 1 | ///! This module implements some arithmetic functions that are valid in a ‘const context”, i.e., |
| 2 | ///! can be computed at compile-time. | |
| 3 | ||
| 4 | /// Calculate $n!$. | |
| 5 | /// (The version in the crate `num_integer` deesn't currently work in a `const` context. | |
| 6 | pub const fn factorial(n : usize) -> usize { | |
| 7 | const fn f(i : usize, a : usize) -> usize { | |
| 8 | if i==0 { a } else { f(i-1, i*a) } | |
| 9 | } | |
| 10 | f(n, 1) | |
| 11 | } | |
| 12 | ||
| 13 | /// Calculate $\nchoosek{n}{k}$. | |
| 14 | /// (The version in the crate `num_integer` deesn't currently work in a `const` context. | |
| 15 | pub const fn binomial(n : usize, k : usize) -> usize { | |
| 16 | factorial(n)/(factorial(n-k)*factorial(k)) | |
| 17 | } | |
| 18 | ||
| 19 | /// Calculate $n^k$. | |
| 20 | /// (The version in the crate `num_integer` deesn't currently work in a `const` context. | |
| 21 | pub const fn pow(n : usize, k : usize) -> usize { | |
| 22 | const fn pow_accum(n : usize, k : usize, accum : usize) -> usize { | |
| 23 | if k==0 { accum } else { pow_accum(n, k-1, accum*n) } | |
| 24 | } | |
| 25 | pow_accum(n, k, 1) | |
| 26 | } |
