diff --git a/lib/fixunssfti.c b/lib/fixunssfti.c
new file mode 100644
index 0000000..b2f47a8
--- /dev/null
+++ b/lib/fixunssfti.c
@@ -0,0 +1,44 @@
+//===-- fixunssfti.c - Implement __fixunssfti -----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements __fixunssfti for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#if __x86_64
+
+#include "int_lib.h"
+
+// Returns: convert a to a unsigned long long, rounding toward zero.
+//          Negative values all become zero.
+
+// Assumption: float is a IEEE 32 bit floating point type 
+//             tu_int is a 64 bit integral type
+//             value in float is representable in tu_int or is negative 
+//                 (no range checking performed)
+
+// seee eeee emmm mmmm mmmm mmmm mmmm mmmm
+
+tu_int
+__fixunssfti(float a)
+{
+    float_bits fb;
+    fb.f = a;
+    int e = ((fb.u & 0x7F800000) >> 23) - 127;
+    if (e < 0 || (fb.u & 0x80000000))
+        return 0;
+    tu_int r = (fb.u & 0x007FFFFF) | 0x00800000;
+    if (e > 23)
+        r <<= (e - 23);
+    else
+        r >>= (23 - e);
+    return r;
+}
+
+#endif