diff --git a/hashset.h b/hashset.h
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+/* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
+/*
+ *     Copyright 2012 Couchbase, Inc.
+ *
+ *   Licensed under the Apache License, Version 2.0 (the "License");
+ *   you may not use this file except in compliance with the License.
+ *   You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *   Unless required by applicable law or agreed to in writing, software
+ *   distributed under the License is distributed on an "AS IS" BASIS,
+ *   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *   See the License for the specific language governing permissions and
+ *   limitations under the License.
+ */
+
+#ifndef HASHSET_H
+#define HASHSET_H 1
+
+#include <stdlib.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+    struct hashset_st {
+        size_t nbits;
+        size_t mask;
+
+        size_t capacity;
+        size_t *items;
+        size_t nitems;
+        size_t n_deleted_items;
+    };
+
+    typedef struct hashset_st *hashset_t;
+
+    /* create hashset instance */
+    hashset_t hashset_create(void);
+
+    /* destroy hashset instance */
+    void hashset_destroy(hashset_t set);
+
+    size_t hashset_num_items(hashset_t set);
+
+    /* add item into the hashset.
+     *
+     * @note 0 and 1 is special values, meaning nil and deleted items. the
+     *       function will return -1 indicating error.
+     *
+     * returns zero if the item already in the set and non-zero otherwise
+     */
+    int hashset_add(hashset_t set, void *item);
+
+    /* remove item from the hashset
+     *
+     * returns non-zero if the item was removed and zero if the item wasn't
+     * exist
+     */
+    int hashset_remove(hashset_t set, void *item);
+
+    /* check if existence of the item
+     *
+     * returns non-zero if the item exists and zero otherwise
+     */
+    int hashset_is_member(hashset_t set, void *item);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif