1 files changed, 45 insertions, 0 deletions
diff --git a/oidset.h b/oidset.h
new file mode 100644
index 0000000000..b7eaab5b88
--- /dev/null
+++ b/oidset.h
@@ -0,0 +1,45 @@
+#ifndef OIDSET_H
+#define OIDSET_H
+
+/**
+ * This API is similar to sha1-array, in that it maintains a set of object ids
+ * in a memory-efficient way. The major differences are:
+ *
+ *   1. It uses a hash, so we can do online duplicate removal, rather than
+ *      sort-and-uniq at the end. This can reduce memory footprint if you have
+ *      a large list of oids with many duplicates.
+ *
+ *   2. The per-unique-oid memory footprint is slightly higher due to hash
+ *      table overhead.
+ */
+
+/**
+ * A single oidset; should be zero-initialized (or use OIDSET_INIT).
+ */
+struct oidset {
+	struct hashmap map;
+};
+
+#define OIDSET_INIT { { NULL } }
+
+/**
+ * Returns true iff `set` contains `oid`.
+ */
+int oidset_contains(const struct oidset *set, const struct object_id *oid);
+
+/**
+ * Insert the oid into the set; a copy is made, so "oid" does not need
+ * to persist after this function is called.
+ *
+ * Returns 1 if the oid was already in the set, 0 otherwise. This can be used
+ * to perform an efficient check-and-add.
+ */
+int oidset_insert(struct oidset *set, const struct object_id *oid);
+
+/**
+ * Remove all entries from the oidset, freeing any resources associated with
+ * it.
+ */
+void oidset_clear(struct oidset *set);
+
+#endif /* OIDSET_H */