code: def _VarintDecoder(mask):
    
  
    def DecodeVarint(buffer, pos):
      result = 0
      shift = 0
      while 1:
        if pos > len(buffer) -1:
          raise NotEnoughDataException( "Not enough data to decode varint" )
        b = buffer[pos]
        result |= ((b & 0x7f) << shift)
        pos += 1
        if not (b & 0x80):
          result &= mask
          return (result, pos)
        shift += 7
        if shift >= 64:
          raise _DecodeError('Too many bytes when decoding varint.')
  
    return DecodeVarint
docs: Return an encoder for a basic varint value (does not include tag).
  
    Decoded values will be bitwise-anded with the given mask before being
    returned, e.g. to limit them to 32 bits.  The returned decoder does not
    take the usual "end" parameter -- the caller is expected to do bounds checking
    after the fact (often the caller can defer such checking until later).  The
    decoder returns a (value, new_pos) pair.