let mask_bits = &src[hdr_size..][..mask_size];
let index_bytes = &src[hdr_size+mask_size..];
validate!(src.len() >= hdr_size + mask_size);
let mask_bits = &src[hdr_size..][..mask_size];
let index_bytes = &src[hdr_size+mask_size..];
validate!(src.len() >= hdr_size + mask_size);