Implement and test retaining multipliers by bit prefix

main.hpp

@@ -55,6 +55,7 @@ extern size_t maximum_string_attribute_length;
 extern std::string accumulate_numeric;
 extern std::string use_h3_index;
 extern unsigned long long preserve_multiplier_density_threshold;
+extern std::vector<int> preserve_multiplier_density_bits_by_zoom;
 
 struct order_field {
 	std::string name;

serial.hpp

@@ -58,6 +58,10 @@ struct serial_val {
 		s = milo::dtoa_milo(val);
 	}
 
+	std::string toString() const {
+		return s;
+	}
+
 	double to_double() const {
 		return atof(s.c_str());
 	}

tile.cpp

@@ -1255,6 +1255,11 @@ static serial_feature next_feature(decompressor *geoms, std::atomic<long long> *
 			} else if (preserve_multiplier_density_threshold > 0 &&
 				   sf.index - next_feature_state.prev_not_dropped_index > ((1LL << (32 - z)) / preserve_multiplier_density_threshold) * ((1LL << (32 - z)) / preserve_multiplier_density_threshold)) {
 				sf.dropped = FEATURE_ADDED_FOR_MULTIPLIER_DENSITY;
+			} else if (preserve_multiplier_density_bits_by_zoom.size() > 0 &&
+				   (size_t) z < preserve_multiplier_density_bits_by_zoom.size() &&
+				   (sf.index >> (64 - preserve_multiplier_density_bits_by_zoom[z])) !=
+					   (next_feature_state.prev_not_dropped_index >> (64 - preserve_multiplier_density_bits_by_zoom[z]))) {
+				sf.dropped = FEATURE_ADDED_FOR_MULTIPLIER_DENSITY;
 			} else {
 				sf.dropped = FEATURE_DROPPED;
 			}