code: def readbits(self, bits):
          
          
          if bits == 0:
              return 0
          
          # fast byte-aligned path
          if bits % 8 == 0 and self._bits_pending == 0:
              return self._read_bytes_aligned(bits // 8)
          
          out = 0
          masks = self._masks
          
          def transfer_bits(x, y, n, t):
              """
              transfers t bits from the top of y_n to the bottom of x.
              then returns x and the remaining bits in y
              """
              if n == t:
                  # taking all
                  return (x << t) | y, 0
              
              mask = masks[t]           # (1 << t) - 1
              remainmask = masks[n - t] # (1 << n - t) - 1
              taken = ((y >> n - t) & mask)
              return (x << t) | taken, y & remainmask
          
          while bits > 0:
              if self._bits_pending > 0:
                  assert self._partial_byte is not None
                  take = min(self._bits_pending, bits)
                  out, self._partial_byte = transfer_bits(out, self._partial_byte, self._bits_pending, take)
                  
                  if take == self._bits_pending:
                      # we took them all
                      self._partial_byte = None
                  self._bits_pending -= take
                  bits -= take
                  continue
              
              r = self.f.read(1)
              if r == b'':
                  raise EOFError
              self._partial_byte = ord(r)
              self._bits_pending = 8
          
          return out
docs: Read the specified number of bits from the stream.
          Returns 0 for bits == 0.