Add new src/oid.h

src/oid.h

+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_oid_h__
+#define INCLUDE_oid_h__
+
+#include "git2/oid.h"
+
+/*
+ * Compare two oid structures.
+ *
+ * @param a first oid structure.
+ * @param b second oid structure.
+ * @return <0, 0, >0 if a < b, a == b, a > b.
+ */
+GIT_INLINE(int) git_oid__cmp(const git_oid *a, const git_oid *b)
+{
+	const unsigned char *sha1 = a->id;
+	const unsigned char *sha2 = b->id;
+	int i;
+
+	for (i = 0; i < GIT_OID_RAWSZ; i++, sha1++, sha2++) {
+		if (*sha1 != *sha2)
+			return *sha1 - *sha2;
+	}
+
+	return 0;
+}
+
+#endif