implement KMP for substring iterator

gistfile1.rs

// uses KMP
fn iter_matches(s:str, sep:str, count:option<uint>, f:fn(uint, uint)) {
    let mut table = [-1, 0],
            calls = 0u;

    let mut pos = 0u, candidate = 0,
            sep_len = str::len(sep);
    while (pos < sep_len) {
        if pos < 2u { pos += 1u; }
        else if sep[pos - 1u] == sep[candidate] {
            candidate += 1;
            table += [candidate];
            pos += 1u;
        }
        else if candidate > 0 {
            candidate = table[candidate];
        }
        else {
            table += [0];
            pos += 1u;
        }
    }

    let mut pos = 0u, match = 0u,
            len = str::len(s);
    while (pos + match < len &&
           alt count { some(c) { calls < c } none { true } }) {
        if (sep[pos] == s[match + pos]) {
            if (pos == sep_len - 1u) {
                f(match, match + pos + 1u);
                calls += 1u;
                match += pos + 1u;
                pos = 0u;
            } else {
                pos += 1u;
            }
        } else {
            match = (match as int + pos as int - table[pos]) as uint;
            pos = if (table[pos] > -1) { table[pos] as uint }
                                  else { 0u };
        }
    }
}