Binary-search with given function in Rust.

binary_search.rs

use std::cmp::Ordering;

pub fn binary_search(max: usize, mut f: impl FnMut(usize) -> Ordering) -> Result<usize, usize> {
    let mut left = 0;
    let mut right = max;
    while left < right {
        let mid = left + (right - left) / 2;
        match f(mid) {
            Ordering::Less => left = mid + 1,
            Ordering::Greater => right = mid - 1,
            Ordering::Equal => return Ok(mid),
        }
    }
    Err(left)
}