chrono_tz/
binary_search.rs

1use core::cmp::Ordering;
2
3/// An implementation of binary search on indices only
4/// that does not require slices to be constructed. Mirrors
5/// the semantics of binary_search_by in the standard library.
6pub fn binary_search<F>(mut start: usize, mut end: usize, mut f: F) -> Result<usize, usize>
7where
8    F: FnMut(usize) -> Ordering,
9{
10    loop {
11        let mid = start + (end - start) / 2;
12        if mid == end {
13            return Err(start);
14        }
15        match f(mid) {
16            Ordering::Less => start = mid + 1,
17            Ordering::Greater => end = mid,
18            Ordering::Equal => return Ok(mid),
19        }
20    }
21}
22
23#[test]
24fn test_binary_search() {
25    assert_eq!(binary_search(0, 5000, |x| x.cmp(&1337)), Ok(1337));
26    assert_eq!(binary_search(0, 5000, |x| x.cmp(&9000)), Err(5000));
27    assert_eq!(binary_search(30, 50, |x| x.cmp(&42)), Ok(42));
28    assert_eq!(binary_search(300, 500, |x| x.cmp(&42)), Err(300));
29    assert_eq!(
30        binary_search(0, 500, |x| if x < 42 { Ordering::Less } else { Ordering::Greater }),
31        Err(42)
32    );
33}