class BinData::IO::Read

def readbits(nbits, endian)

the bits are stored in +:big+ or +:little+ endian format.
Reads exactly +nbits+ bits from the stream. +endian+ specifies whether 
def readbits(nbits, endian)
  if @rendian != endian
    # don't mix bits of differing endian
    reset_read_bits
    @rendian = endian
  end
  if endian == :big
    read_big_endian_bits(nbits)
  else
    read_little_endian_bits(nbits)
  end
end