Add a get function that can help handle duplicate key entries.

include/ht.h

@@ -125,6 +125,16 @@ libds_result ht_put(ht* ht, const void* key, void* value);
  * @return the data, or NULL if it is not found.
  */
 void* ht_get(ht* ht, const void* key);
+/**
+ * Retreives the first value from the hash table
+ * that's stored with the given key and passes the compare function.
+ * @param ht the hash table to retreive the value from.
+ * @param key the key to use to find the data.
+ * @param data the data to compare the candidate value to.
+ * @param compare the comparison function used to compare adta.
+ * @return the data, or NULL if it is not found.
+ */
+void* ht_get_filter(ht* ht, const void* key, void* data, compare_func compare);
 /**
  * Removes a value from the hash table.
  * @param ht the hash table to remove a value from.

src/ht.c

@@ -84,6 +84,21 @@ void* ht_get(ht* ht, const void* key) {
 
   return data;
 }
+void* ht_get_filter(ht* ht, const void* key, void* data, compare_func compare) {
+  void* found = NULL;
+  ht_node* search_node;
+  unsigned long key_int = ht->hash_func(key) % LIBDS_HT_SIZE;
+
+  search_node = ht->data[key_int];
+  while (search_node && found == NULL) {
+    if (ht->cmp_func(search_node->key, key) &&
+        compare(data, search_node->data)) {
+      found = search_node->data;
+    }
+    search_node = search_node->next;
+  }
+  return found;
+}
 void ht_remove(ht* ht, const void* key) {
   ht_node** search_ptr;
   unsigned long key_int = ht->hash_func(key) % LIBDS_HT_SIZE;