hashmap: add string interning API

[thirdparty/git.git] / hashmap.c

diff --git a/hashmap.c b/hashmap.c
index d1b8056d8d53c35d62599999026766a4342eb764..f693839cb4786fd5be57d878b58499273ec17f81 100644 (file)
--- a/hashmap.c
+++ b/hashmap.c
@@ -226,3 +226,41 @@ void *hashmap_iter_next(struct hashmap_iter *iter)
                current = iter->map->table[iter->tablepos++];
        }
 }
+
+struct pool_entry {
+       struct hashmap_entry ent;
+       size_t len;
+       unsigned char data[FLEX_ARRAY];
+};
+
+static int pool_entry_cmp(const struct pool_entry *e1,
+                         const struct pool_entry *e2,
+                         const unsigned char *keydata)
+{
+       return e1->data != keydata &&
+              (e1->len != e2->len || memcmp(e1->data, keydata, e1->len));
+}
+
+const void *memintern(const void *data, size_t len)
+{
+       static struct hashmap map;
+       struct pool_entry key, *e;
+
+       /* initialize string pool hashmap */
+       if (!map.tablesize)
+               hashmap_init(&map, (hashmap_cmp_fn) pool_entry_cmp, 0);
+
+       /* lookup interned string in pool */
+       hashmap_entry_init(&key, memhash(data, len));
+       key.len = len;
+       e = hashmap_get(&map, &key, data);
+       if (!e) {
+               /* not found: create it */
+               e = xmallocz(sizeof(struct pool_entry) + len);
+               hashmap_entry_init(e, key.ent.hash);
+               e->len = len;
+               memcpy(e->data, data, len);
+               hashmap_add(&map, e);
+       }
+       return e->data;
+}