impl <'a> IntoIterator for &'a Bitmap {
    type Item = u16;
    type IntoIter = SharedBitmapIterator<'a>;
    fn into_iter(self) -> Self::IntoIter {
        return SharedBitmapIterator { offset: 0, bitmap: &self };
    }
}

impl IntoIterator for Bitmap {
    type Item = u16;
    type IntoIter = OwnedBitmapIterator;
    fn into_iter(self) -> Self::IntoIter {
        return OwnedBitmapIterator { offset: 0, bitmap: self };
    }
}


pub struct SharedBitmapIterator<'a> {
    offset: usize,
    bitmap: &'a Bitmap,
}


pub struct OwnedBitmapIterator {
    offset: usize,
    bitmap: Bitmap,
}


impl <'a> Iterator for SharedBitmapIterator<'a> {
    type Item = u16;

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            let bucket = self.offset / BITS_PER_BUCKET;
            let bit_pos = self.offset % BITS_PER_BUCKET;

            if bucket >= self.bitmap.num_buckets() {
                return None;
            }

            // Optimization: skip whole bucket when its value is zero.
            if self.bitmap.buckets[bucket] == 0 {
                self.offset += 64;
                continue;
            }

            if self.bitmap.buckets[bucket] & (1 << bit_pos) == 0 {
                self.offset += 1;
                continue;
            }

            let x = self.offset;
            self.offset += 1;
            return Some(x as u16);
        }
    }
}


impl Iterator for OwnedBitmapIterator {
    type Item = u16;

    fn next(&mut self) -> Option<Self::Item> {
        loop {
            let bucket = self.offset / BITS_PER_BUCKET;
            let bit_pos = self.offset % BITS_PER_BUCKET;

            if bucket >= self.bitmap.num_buckets() {
                return None;
            }

            // Optimization: skip whole bucket when its value is zero.
            if self.bitmap.buckets[bucket] == 0 {
                self.offset += 64;
                continue;
            }

            if self.bitmap.buckets[bucket] & (1 << bit_pos) == 0 {
                self.offset += 1;
                continue;
            }

            let x = self.offset;
            self.offset += 1;
            return Some(x as u16);
        }
    }
}