class BinData::IO

def write_big_endian_bits(val, nbits)
  while nbits > 0
    bits_req = 8 - @wnbits
    if nbits >= bits_req
      msb_bits = (val >> (nbits - bits_req)) & mask(bits_req)
      nbits -= bits_req
      val &= mask(nbits)
      @wval   = (@wval << bits_req) | msb_bits
      @raw_io.write(@wval.chr)
      @wval   = 0
      @wnbits = 0
    else
      @wval = (@wval << nbits) | val
      @wnbits += nbits
      nbits = 0
    end
  end
end