Speeding up tippecanoe-overzoom (#191)

* Speed up mvt_value comparison

* Converting repetitive ifs to cases

* More conversions from ifs to cases

* Optimize the always-true filter case

* Don't convert types of attributes without accumulators

* Unordered map seems to be faster than map

* Add missing header

* Fix some warnings

* Fix the warnings better

* Avoid an int->string->int conversion

* Lazily initialize layer key and values maps when actually needed

* More switches from maps to unordered_maps

* Sure, I'll take the microoptimization

* More emplacement

* Save some copies

* Emplaces and moves

* Lazy linear scan of attributes instead of building a map

* Extra printfs, missing header

* Avoid clipping if the input and output tiles are the same

* But do clip if the tile extent is being reduced

* Make sure I'm not constructing std::strings here at runtime

* More worrying about runtime string construction

* A couple more std::moves

* Const references!

* More const references

* Another std::move

* Make the string_value of mvt_value std::optional

* Reserve storage when decoding

* Provision for different mvt_values to share a string pool

* Use the string pool when decoding

* Avoid another string construction

* Try limiting the depth of the search for duplicate attributes

* Revert "Try limiting the depth of the search for duplicate attributes"

This reverts commit 9ec94a15ff.

* Update changelog

* Fix typo noticed during code review

pmtiles/pmtiles.hpp

@@ -166,11 +166,11 @@ struct entryv3 {
 	}
 };
 
-struct {
+struct entryv3_cmp {
 	bool operator()(entryv3 a, entryv3 b) const {
 		return a.tile_id < b.tile_id;
 	}
-} entryv3_cmp;
+};
 
 struct entry_zxy {
 	uint8_t z;
@@ -388,7 +388,7 @@ inline uint64_t zxy_to_tileid(uint8_t z, uint32_t x, uint32_t y) {
 	if (z > 31) {
 		throw std::overflow_error("tile zoom exceeds 64-bit limit");
 	}
-	if (x > (1 << z) - 1 || y > (1 << z) - 1) {
+	if (x > (1U << z) - 1 || y > (1U << z) - 1) {
 		throw std::overflow_error("tile x/y outside zoom level bounds");
 	}
 	uint64_t acc = 0;