USING: kernel locals accessors math sequences math.bitwise ;

TUPLE: bit-reader byte-array current-pos current-bit ;

: <bit-reader> ( bytearray -- bitreader ) 0 0 bit-reader boa ;

: advance ( reader -- reader )
    0 >>current-bit [ 1 + ] change-current-pos ;

: ?advance ( reader -- reader )
    dup current-bit>> 8 = [ advance ] when ;

:: read-single-value ( bits reader -- result )
    reader current-pos>> reader byte-array>> nth
    reader current-bit>> [ bits 1 - + ] keep bit-range
    reader [ bits + ] change-current-bit ?advance drop ;

: bits-left ( reader -- n )
    current-bit>> 8 swap - ;

DEFER: read-bits

:: read-multi-value ( bits reader -- result )
    reader bits-left :> extra-bits
    extra-bits reader read-single-value
    bits extra-bits - reader read-bits
    extra-bits shift + ;

: read-bits ( bits reader -- result )
    2dup current-bit>> + 8 < [
        read-single-value
    ] [
        read-multi-value
    ] if ;