Use 32-bit offsets in the string pool search tree to reduce its size

pool.cpp

@@ -35,7 +35,7 @@ int swizzlecmp(const char *a, const char *b) {
 }
 
 long long addpool(struct memfile *poolfile, struct memfile *treefile, const char *s, char type) {
-	long long *sp = &treefile->tree;
+	unsigned long *sp = &treefile->tree;
 	size_t depth = 0;
 
 	// In typical data, traversal depth generally stays under 2.5x
@@ -95,6 +95,16 @@ long long addpool(struct memfile *poolfile, struct memfile *treefile, const char
 		exit(EXIT_FAILURE);
 	}
 
+	if (off >= LONG_MAX || treefile->off >= LONG_MAX) {
+		// Tree or pool is bigger than 2GB
+		static bool warned = false;
+		if (!warned) {
+			fprintf(stderr, "Warning: string pool is very large.\n");
+			warned = true;
+		}
+		return off;
+	}
+
 	struct stringpool tsp;
 	tsp.left = 0;
 	tsp.right = 0;