if !self.index.is_empty() {
self.bw.write_buf(b"idx1")?;
self.bw.write_u32le((self.index.len() * 16) as u32)?;
for item in self.index.iter() {
if !self.index.is_empty() {
self.bw.write_buf(b"idx1")?;
self.bw.write_u32le((self.index.len() * 16) as u32)?;
for item in self.index.iter() {