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

text.cpp

@@ -184,3 +184,44 @@ char *dtoa_milo(double val) {
 	}
 	return dup;
 }
+
+unsigned long long fnv1a(std::string const &s) {
+	// Store tiles by a hash of their contents (fnv1a 64-bit)
+	// http://www.isthe.com/chongo/tech/comp/fnv/
+	const unsigned long long fnv_offset_basis = 14695981039346656037u;
+	const unsigned long long fnv_prime = 1099511628211u;
+	unsigned long long h = fnv_offset_basis;
+	for (size_t i = 0; i < s.size(); i++) {
+		h ^= (unsigned char) s[i];
+		h *= fnv_prime;
+	}
+	return h;
+}
+
+// The "additional" is to make it easier to hash a serial_val attribute value and type together
+unsigned long long fnv1a(const char *s, char additional) {
+	// http://www.isthe.com/chongo/tech/comp/fnv/
+	const unsigned long long fnv_offset_basis = 14695981039346656037u;
+	const unsigned long long fnv_prime = 1099511628211u;
+	unsigned long long h = fnv_offset_basis;
+	for (size_t i = 0; s[i] != '\0'; i++) {
+		h ^= (unsigned char) s[i];
+		h *= fnv_prime;
+	}
+	h ^= (unsigned char) additional;
+	h *= fnv_prime;
+	return h;
+}
+
+unsigned long long fnv1a(size_t size, void *p) {
+	// http://www.isthe.com/chongo/tech/comp/fnv/
+	unsigned char *s = (unsigned char *) p;
+	const unsigned long long fnv_offset_basis = 14695981039346656037u;
+	const unsigned long long fnv_prime = 1099511628211u;
+	unsigned long long h = fnv_offset_basis;
+	for (size_t i = 0; i < size; i++) {
+		h ^= (unsigned char) s[i];
+		h *= fnv_prime;
+	}
+	return h;
+}