Much faster to search and add to the string pool as a binary tree

geojson.c

@@ -139,25 +139,42 @@ struct pool_val *pool(struct pool *p, char *s, int type) {
 
 		if (cmp == 0) {
 			return *v;
+		} else if (cmp < 0) {
+			v = &((*v)->left);
+		} else {
+			v = &((*v)->right);
 		}
-
-		v = &((*v)->next);
 	}
 
 	*v = malloc(sizeof(struct pool_val));
+	(*v)->left = NULL;
+	(*v)->right = NULL;
 	(*v)->next = NULL;
 	(*v)->s = s;
 	(*v)->type = type;
 	(*v)->n = p->n++;
+
+	if (p->tail != NULL) {
+		p->tail->next = *v;
+	}
+	p->tail = *v;
+	if (p->head == NULL) {
+		p->head = *v;
+	}
+
 	return *v;
 }
 
 void pool_free(struct pool *p) {
-	while (p->vals != NULL) {
-		struct pool_val *next = p->vals->next;
-		free(p->vals);
-		p->vals = next;
+	while (p->head != NULL) {
+		struct pool_val *next = p->head->next;
+		free(p->head);
+		p->head = next;
 	}
+
+	p->head = NULL;
+	p->tail = NULL;
+	p->vals = NULL;
 }
 
 

tile.cc

@@ -59,6 +59,8 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 	struct pool keys;
 	keys.n = 0;
 	keys.vals = NULL;
+	keys.head = NULL;
+	keys.tail = NULL;
 
 	struct index *i;
 	//printf("tile -----------------------------------------------\n");
@@ -165,7 +167,7 @@ void write_tile(struct index *start, struct index *end, char *metabase, unsigned
 	}
 
 	struct pool_val *pv;
-	for (pv = keys.vals; pv != NULL; pv = pv->next) {
+	for (pv = keys.head; pv != NULL; pv = pv->next) {
 		layer->add_keys(pv->s, strlen(pv->s));
 	}
 	pool_free(&keys);

tile.h

@@ -19,11 +19,17 @@ struct pool_val {
 	int type;
 	int n;
 
+	struct pool_val *left;
+	struct pool_val *right;
+
 	struct pool_val *next;
 };
 
 struct pool {
 	struct pool_val *vals;
+
+	struct pool_val *head;
+	struct pool_val *tail;
 	int n;
 };