Method has_visited

regex/src/backtrack.rs:285–295

(&mut self, ip: InstPtr, at: InputAt)

    }

    fn has_visited(&mut self, ip: InstPtr, at: InputAt) -> bool {
        let k = ip * (self.input.len() + 1) + at.pos();
        let k1 = k / BIT_SIZE;
        let k2 = usize_to_u32(1 << (k & (BIT_SIZE - 1)));
        if self.m.visited[k1] & k2 == 0 {
            self.m.visited[k1] |= k2;
            false
        } else {
            true
        }
    }
}

fn usize_to_u32(n: usize) -> u32 {