thodg/libgit2

diff --git a/src/oid.h b/src/oid.h
index aa1f0bf..922a2a3 100644
--- a/src/oid.h
+++ b/src/oid.h
@@ -44,4 +44,13 @@ GIT_INLINE(int) git_oid__cmp(const git_oid *a, const git_oid *b)
 	return git_oid__hashcmp(a->id, b->id);
 }
 
+GIT_INLINE(void) git_oid__cpy_prefix(
+	git_oid *out, const git_oid *id, size_t len)
+{
+	memcpy(&out->id, id->id, (len + 1) / 2);
+
+	if (len & 1)
+		out->id[len / 2] &= 0xF0;
+}
+
 #endif