cmap format4_segments_fast.rs

struct Segment {
    start: u16,
    end: u16,
    id_delta: i16,
}

fn format4_segments_fast(map: &BTreeMap<char, u32>) -> Vec<Segment> {
    let mut segments = Vec::<Segment>::new();

    if map.is_empty() {
        return segments;
    }

    let mut previous_cid: u32 = 0;
    let mut previous_gid: u32 = 0;
    let mut start_cid: u32 = 0;
    let mut id_delta: i64 = 0;

    for (c, gid) in map {
        let cid = *c as u32;

        if cid > 0xFFFF {
            break;
        }

        let gid = *gid;

        id_delta = (gid as i64) - (cid as i64);

        if start_cid == 0 {
            start_cid = cid;
        } else if previous_cid + 1 != cid || previous_gid + 1 != gid {
            let segment = Segment {
                start: start_cid as u16,
                end: previous_cid as u16,
                id_delta: id_delta as i16,
            };
            segments.push(segment);
            start_cid = cid;
        }

        previous_cid = cid;
        previous_gid = gid;
    }

    let segment = Segment {
        start: start_cid as u16,
        end: previous_cid as u16,
        id_delta: id_delta as i16,
    };
    segments.push(segment);

    segments
}