Use differential encoding for name offsets

Each name is represented as an integer range in a vector of chars.
Instead of storing the absolute offset inside this array, we can store
only the offset to the previous entry (the string size). By doing this we reduce
the number of bytes need to store an offset from 4 to 1 bytes (if we
set a maximum string length of 255).
This is however slower, since the absolute offset must be computed on
each querry by summing up all previous lengths. To limit the
performance inpact we only do this for blocks of a certain size (16).

Extractor/ExtractionContainers.cpp

@@ -395,32 +395,19 @@ void ExtractionContainers::PrepareData(const std::string &output_file_name,
         std::string name_file_streamName = (output_file_name + ".names");
         boost::filesystem::ofstream name_file_stream(name_file_streamName, std::ios::binary);
 
-        // write number of names
-        const unsigned number_of_names = name_list.size() + 1;
-        name_file_stream.write((char *)&(number_of_names), sizeof(unsigned));
+        std::vector<unsigned> name_lengths;
+        for (const std::string &temp_string : name_list)
+        {
+            name_lengths.push_back(temp_string.length());
+        }
 
-        // compute total number of chars
-        unsigned total_number_of_chars = 0;
-        for (const std::string &temp_string : name_list)
-        {
-            total_number_of_chars += temp_string.length();
-        }
-        // write total number of chars
-        name_file_stream.write((char *)&(total_number_of_chars), sizeof(unsigned));
-        // write prefixe sums
-        unsigned name_lengths_prefix_sum = 0;
-        for (const std::string &temp_string : name_list)
-        {
-            name_file_stream.write((char *)&(name_lengths_prefix_sum), sizeof(unsigned));
-            name_lengths_prefix_sum += temp_string.length();
-        }
-        // duplicate on purpose!
-        name_file_stream.write((char *)&(name_lengths_prefix_sum), sizeof(unsigned));
+        RangeTable<> table(name_lengths);
+        name_file_stream << table;
 
         // write all chars consecutively
         for (const std::string &temp_string : name_list)
         {
-            const unsigned string_length = temp_string.length();
+            const unsigned string_length = std::min(temp_string.length(), 255lu);
             name_file_stream.write(temp_string.c_str(), string_length);
         }