def decode_positions(self, valuestring):
     read = StringIO(valuestring).read
     freq = unpack_uint(read(_INT_SIZE))[0]
     position = 0
     positions = []
     for _ in xrange(freq):
         position = read_varint(read) + position
         positions.append(position)
     return positions

 def decode_characters(self, valuestring):
     read = StringIO(valuestring).read
     freq = unpack_uint(read(_INT_SIZE))[0]
     position = 0
     endchar = 0
     posns_chars = []
     for _ in xrange(freq):
         position = read_varint(read) + position
         startchar = endchar + read_varint(read)
         endchar = startchar + read_varint(read)
         posns_chars.append((position, startchar, endchar))
     return posns_chars

 def decode_position_boosts(self, valuestring):
     f = StringIO(valuestring)
     read = f.read
     freq = unpack_uint(read(_INT_SIZE))[0]
     
     # Skip summed boost
     f.seek(_FLOAT_SIZE, 1)
     
     position = 0
     posns_boosts = []
     for _ in xrange(freq):
         position = read_varint(read) + position
         boost = byte_to_float(read(1))
         posns_boosts.append((position, boost))
     return posns_boosts

 def decode_character_boosts(self, valuestring):
     f = StringIO(valuestring)
     read = f.read
     
     freq = unpack_uint(read(_INT_SIZE))[0]
     # Skip summed boost
     f.seek(_FLOAT_SIZE, 1)
     
     position = 0
     endchar = 0
     posns_chars = []
     for _ in xrange(freq):
         position = read_varint(read) + position
         startchar = endchar + read_varint(read)
         endchar = startchar + read_varint(read)
         boost = byte_to_float(read(1))
         posns_chars.append((position, startchar, endchar, boost))
     return posns_chars

 def get_uint(self, position):
     return unpack_uint(self.map[position:position + _INT_SIZE])[0]

 def read_uint(self):
     return unpack_uint(self.file.read(_INT_SIZE))[0]

 def decode_frequency(self, valuestring):
     return unpack_uint(valuestring[:_INT_SIZE])[0]

 def decode_weight(self, valuestring):
     freq = unpack_uint(valuestring)[0]
     return freq * self.field_boost

 def get_uint(self, position):
     return unpack_uint(self.get(position, _INT_SIZE))[0]

 def decode_weight(self, valuestring):
     freq = unpack_uint(valuestring[:_INT_SIZE])[0]
     docboost = byte_to_float(valuestring[-1])
     return freq * docboost * self.field_boost

 def decode_docboosts(self, valuestring):
     freq = unpack_uint(valuestring[:_INT_SIZE])[0]
     docboost = byte_to_float(valuestring[-1])
     return (freq, docboost)