diff --git a/lib/fixdfti.c b/lib/fixdfti.c
new file mode 100644
index 0000000..94fc8d3
--- /dev/null
+++ b/lib/fixdfti.c
@@ -0,0 +1,43 @@
+//===-- fixdfti.c - Implement __fixdfti -----------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements __fixdfti for the compiler_rt library.
+//
+//===----------------------------------------------------------------------===//
+
+#if __x86_64
+
+#include "int_lib.h"
+
+// Returns: convert a to a signed long long, rounding toward zero.
+
+// Assumption: double is a IEEE 64 bit floating point type 
+//             su_int is a 32 bit integral type
+//             value in double is representable in ti_int (no range checking performed)
+
+// seee eeee eeee mmmm mmmm mmmm mmmm mmmm | mmmm mmmm mmmm mmmm mmmm mmmm mmmm mmmm
+
+ti_int
+__fixdfti(double a)
+{
+    double_bits fb;
+    fb.f = a;
+    int e = ((fb.u.high & 0x7FF00000) >> 20) - 1023;
+    if (e < 0)
+        return 0;
+    ti_int s = (si_int)(fb.u.high & 0x80000000) >> 31;
+    ti_int r = 0x0010000000000000uLL | (0x000FFFFFFFFFFFFFuLL & fb.u.all);
+    if (e > 52)
+        r <<= (e - 52);
+    else
+        r >>= (52 - e);
+    return (r ^ s) - s;
+}
+
+#endif