Switch mean over to internal accumulation state

attribute.cpp

@@ -120,19 +120,13 @@ static void preserve_attribute1(attribute_op const &op, std::string const &key,
 			}
 
 			case op_mean: {
-				auto state = attribute_accum_state.find(key);
-				if (state == attribute_accum_state.end()) {
-					accum_state s;
-					s.sum = full_values[i].to_double() + val.to_double();
-					s.count = 2;
-					attribute_accum_state.insert(std::pair<std::string, accum_state>(key, s));
-
-					full_values[i] = (s.sum / s.count);
+				size_t count = full_values[i].get_count();
+				if (count <= 1) {
+					full_values[i].set_double_count((full_values[i].to_double() + val.to_double()) / 2, 2);
 				} else {
-					state->second.sum += val.to_double();
-					state->second.count += 1;
-
-					full_values[i] = (state->second.sum / state->second.count);
+					double sum = full_values[i].to_double() * count + val.to_double();
+					count++;
+					full_values[i].set_double_count(sum / count, count);
 				}
 				return;
 			}

mvt.hpp

@@ -159,7 +159,7 @@ struct mvt_value {
 		this->count = 0;
 	}
 
-	void set_double_accum(double v, size_t c) {
+	void set_double_count(double v, size_t c) {
 		this->type = mvt_double;
 		this->numeric_value.double_value = v;
 		this->count = c;

serial.hpp

@@ -80,7 +80,7 @@ struct serial_val {
 		}
 	}
 
-	void set_double_accum(double v, size_t c) {
+	void set_double_count(double v, size_t c) {
 		type = mvt_double;
 		s = milo::dtoa_milo(v) + '\0' + std::to_string(c);
 	}

tile.cpp

@@ -2370,6 +2370,11 @@ long long write_tile(decompressor *geoms, std::atomic<long long> *geompos_in, ch
 				if (p.need_tilestats.size() > 0) {
 					for (size_t j = 0; j < p.full_keys.size(); j++) {
 						if (p.need_tilestats.count(*p.full_keys[j]) > 0) {
+							// remove accumulation state
+							size_t found = p.full_values[j].s.find('\0');
+							if (found != std::string::npos) {
+								p.full_values[j].s = p.full_values[j].s.substr(0, found);
+							}
 							add_tilestats(layername, z, layermaps, tiling_seg, layer_unmaps, *p.full_keys[j], p.full_values[j]);
 						}
 					}