horspool search algorithm in rust

horspool.rs

fn horspool<T: Eq+Hash>(haystack: &[T], needle: &[T]) -> isize {
    let hlen = haystack.len();
    let nlen = needle.len();
    if nlen == 0 { return 0 }
    // jump table
    let jmp: HashMap<&T, usize> = needle.iter().zip((1..nlen).rev()).collect();
    let last = nlen - 1;
    let mut j = 0;
    while j <= hlen - nlen {
        // search backward
        let mut i = last;
        while haystack[j + i] == needle[i] {
            if i == 0 {/* found */ return j as isize }
            i -= 1
        }
        // jump according to the last one of haystack
        j += *jmp.get(&haystack[j + last]).unwrap_or(&nlen);
    }
    /* not found */ -1
}