Bit size array
I trying parse payload of AMR protocol. [Protocol description](https://datatracker.ietf.org/doc/html/rfc4867#section-4.3.5.1).
Briefly protocol has CMR (4 bits), F (1bit last frame in this payload), FT (4bits bitrate), Q(1bit).  Futher protocol has frames with data and padding bits. Frame is bit arrays with variable length. How to create bit array with variable length( length in bits = FT * 20 /1000)?