Externalizing polygon shard detection (#146)

* Start of externalizing polygon shard detection

* Completely untested external quicksort

* Add unit test for external quicksort

* Remember to clean up temporary files

* Sort and scan the vertices

* Bring over more vertex logic

* Make nodes from vertices

* Checkpoint on switching over to global shared nodes

* Do the thing

* Revert unintended change to coalesced linestring behavior

* Take shared nodes into account in early simplification

* Let it do more sorting in memory

* Fix overnoding of collinear linestrings

* Remove duplicate nodes, since only duplicate vertices now matter

* Remember to delete temporary files

* Fix out of bounds memory access below, apparently

* Fix the actual undefined behavior

* Still running out of memory in one case. Find out where.

* Forgot the conditional

* Try again to make it not run out of memory

* Update version and changelog

unit.cpp

@@ -1,6 +1,9 @@
 #define CATCH_CONFIG_MAIN
 #include "catch/catch.hpp"
 #include "text.hpp"
+#include "sort.hpp"
+#include <unistd.h>
+#include <limits.h>
 
 TEST_CASE("UTF-8 enforcement", "[utf8]") {
 	REQUIRE(check_utf8("") == std::string(""));
@@ -18,3 +21,47 @@ TEST_CASE("UTF-8 truncation", "[trunc]") {
 	REQUIRE(truncate16("0123456789😀😬😁😂😃😄😅😆", 17) == std::string("0123456789😀😬😁"));
 	REQUIRE(truncate16("0123456789あいうえおかきくけこさ", 16) == std::string("0123456789あいうえおか"));
 }
+
+int intcmp(const void *v1, const void *v2) {
+	return *((int *) v1) - *((int *) v2);
+}
+
+TEST_CASE("External quicksort", "fqsort") {
+	std::vector<FILE *> inputs;
+
+	size_t written = 0;
+	for (size_t i = 0; i < 5; i++) {
+		std::string tmpname = "/tmp/in.XXXXXXX";
+		int fd = mkstemp((char *) tmpname.c_str());
+		unlink(tmpname.c_str());
+		FILE *f = fdopen(fd, "w+b");
+		inputs.emplace_back(f);
+		size_t iterations = 2000 + rand() % 200;
+		for (size_t j = 0; j < iterations; j++) {
+			int n = rand();
+			fwrite((void *) &n, sizeof(int), 1, f);
+			written++;
+		}
+		rewind(f);
+	}
+
+	std::string tmpname = "/tmp/out.XXXXXX";
+	int fd = mkstemp((char *) tmpname.c_str());
+	unlink(tmpname.c_str());
+	FILE *f = fdopen(fd, "w+b");
+
+	fqsort(inputs, sizeof(int), intcmp, f, 256);
+	rewind(f);
+
+	int prev = INT_MIN;
+	int here;
+	size_t nread = 0;
+	while (fread((void *) &here, sizeof(int), 1, f)) {
+		REQUIRE(here >= prev);
+		prev = here;
+		nread++;
+	}
+
+	fclose(f);
+	REQUIRE(nread == written);
+}