diff --git a/lib/ucmpdi2.c b/lib/ucmpdi2.c
new file mode 100644
index 0000000..dec476f
--- /dev/null
+++ b/lib/ucmpdi2.c
@@ -0,0 +1,36 @@
+//===-- ucmpdi2.c - Implement __ucmpdi2 -----------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements __ucmpdi2 for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#include "int_lib.h"
+
+// Returns:  if (a <  b) returns 0
+//           if (a == b) returns 1
+//           if (a >  b) returns 2
+
+si_int
+__ucmpdi2(du_int a, du_int b)
+{
+    udwords x;
+    x.all = a;
+    udwords y;
+    y.all = b;
+    if (x.high < y.high)
+        return 0;
+    if (x.high > y.high)
+        return 2;
+    if (x.low < y.low)
+        return 0;
+    if (x.low > y.low)
+        return 2;
+    return 1;
+}