Improve tiling speed (#195)

* Add a way to run tippecanoe single-threaded for profiling

* Do less work when the tilestats sample values list is already full

* Save a copy when retrieving the attribute key

* Fewer atomic operations

* Move string hashing from mbtiles to text

* Only do approximate attribute deduplication when writing tiles

* Feature dropping tests are sensitive to exact tile size

* All tile creators now create a string pool for the tile

* Features clipped away to nothing should not participate in that tile

* Revert "Only do approximate attribute deduplication when writing tiles"

This reverts commit c42b34b498.

* Also revert the related test changes

* Revert "Revert "Only do approximate attribute deduplication when writing tiles""

This reverts commit 18509876c3.

* Be more specific about the string hash function

* Use fnv1a instead of std::hash for everything

* Reduce the chance of hash collisions

* Stick a hash search on the front of the tree search in addpool

* Eliminate repeated hashing of the same string

* Switch instead of ifs in json parsing

* A few more cases to populate the hash in addpool

* Store the hash in the tree instead of recalculating

* Add explanatory comment for mysterious argument

* Fewer copies in attribute stringification

* Clean up ancient weirdness in JSON attribute stringification

* More serial_val cleanup

* Pass a serial_feature to rewrite instead of many broken-down arguments

* Get rid of the multiple geometries within `partial`

* Revert "Pass a serial_feature to rewrite instead of many broken-down arguments"

This reverts commit 6f4ab9b725.

* Goodbye, struct coalesce

* Revert "Features clipped away to nothing should not participate in that tile"

This reverts commit 124462fbdc.

* Migrating fields from partial to serial_feature

* Name reconciliation between serial_feature and partial

* Replace struct partial with an augmented serial_feature

* Fix some overzealous search-and-replace renaming

* Don't say struct so often

* Remove more of the former partial construction

* Commenting and cleaning up

* Trying again to avoid all these arguments to rewrite

* I swear I did this same thing before and it didn't work.

* More rewrite cleanup

* Exile --detect-shared-borders to its own file

* Add missing headers

* More commenting and cleanup

* More comments

* Sprinkle consts around

* Emplacing and std::moving

* More cleanup

* That shouldn't have worked after a std::move

* Don't need to allocate memory to compare keys

* Reduce use of the global string pool in tiling

* Another avoidable mvt_value construction

* Further reduction to explicit string pool passing

* These reverses are no longer optimizations

* These layernames can all be references

* Don't drag an unused layername string around with every feature

* Heed a compiler warning about potential buffer overflow

* Fix my confusion about which feature's string pool is relevant

* Avoid some unnecessary allocations in attribute accumulation

* Maybe faster serialization?

* Eliminate a comparison

* Do the same here

* Save a couple of allocations when parsing numbers in JSON

* Immediately assign features to layers instead of subdividing later

* Maintain tilestats for tippecanoe:retain_points_multiplier_sequence

* Crunch out more duplicate attribute values when writing out the tile

* Do tilestats for tippecanoe:retain_points_multiplier_first too

* Shell filters need to be real threads, even if nothing else does

* Simplify tippecanoe_minzoom/maxzoom representation

* Update version and changelog

read_json.cpp

@@ -13,6 +13,7 @@
 #include "mvt.hpp"
 #include "milo/dtoa_milo.h"
 #include "errors.hpp"
+#include "serial.hpp"
 
 const char *geometry_names[GEOM_TYPES] = {
 	"Point",
@@ -120,54 +121,48 @@ void parse_geometry(int t, json_object *j, drawvec &out, int op, const char *fna
 // type and stringified value. All numeric values, even if they are integers,
 // even integers that are too large to fit in a double but will still be
 // stringified with their original precision, are recorded here as mvt_double.
-void stringify_value(json_object *value, int &type, std::string &stringified, const char *reading, int line, json_object *feature) {
+serial_val stringify_value(json_object *value, const char *reading, int line, json_object *feature) {
+	serial_val sv;
+
 	if (value != NULL) {
 		int vt = value->type;
-		std::string val;
 
 		if (vt == JSON_STRING) {
-			val = value->value.string.string;
-		} else if (vt == JSON_NUMBER) {
-			if (value->value.number.large_unsigned != 0) {
-				val = std::to_string(value->value.number.large_unsigned);
-			} else if (value->value.number.large_signed != 0) {
-				val = std::to_string(value->value.number.large_signed);
-			} else {
-				val = milo::dtoa_milo(value->value.number.number);
-			}
-		} else if (vt == JSON_TRUE) {
-			val = "true";
-		} else if (vt == JSON_FALSE) {
-			val = "false";
-		} else if (vt == JSON_NULL) {
-			val = "null";
-		} else {
-			const char *v = json_stringify(value);
-			val = std::string(v);
-			free((void *) v);  // stringify
-		}
+			sv.type = mvt_string;
+			sv.s = value->value.string.string;
 
-		if (vt == JSON_STRING) {
-			type = mvt_string;
-			stringified = val;
-			std::string err = check_utf8(val);
-			if (err != "") {
+			std::string err = check_utf8(sv.s);
+			if (err.size() > 0) {
 				fprintf(stderr, "%s:%d: %s: ", reading, line, err.c_str());
 				json_context(feature);
 				exit(EXIT_UTF8);
 			}
 		} else if (vt == JSON_NUMBER) {
-			type = mvt_double;
-			stringified = val;
-		} else if (vt == JSON_TRUE || vt == JSON_FALSE) {
-			type = mvt_bool;
-			stringified = val;
+			sv.type = mvt_double;
+
+			if (value->value.number.large_unsigned != 0) {
+				sv.s = std::to_string(value->value.number.large_unsigned);
+			} else if (value->value.number.large_signed != 0) {
+				sv.s = std::to_string(value->value.number.large_signed);
+			} else {
+				sv.s = milo::dtoa_milo(value->value.number.number);
+			}
+		} else if (vt == JSON_TRUE) {
+			sv.type = mvt_bool;
+			sv.s = "true";
+		} else if (vt == JSON_FALSE) {
+			sv.type = mvt_bool;
+			sv.s = "false";
 		} else if (vt == JSON_NULL) {
-			type = mvt_null;
-			stringified = "null";
+			sv.type = mvt_null;
+			sv.s = "null";
 		} else {
-			type = mvt_string;
-			stringified = val;
+			sv.type = mvt_string;
+			const char *v = json_stringify(value);
+			sv.s = std::string(v);
+			free((void *) v);  // stringify
 		}
 	}
+
+	return sv;
 }