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diff --git a/UnixPkg/Library/UnixBaseLib/HighBitSet64.c b/UnixPkg/Library/UnixBaseLib/HighBitSet64.c
new file mode 100644
index 0000000000..23abb735be
--- /dev/null
+++ b/UnixPkg/Library/UnixBaseLib/HighBitSet64.c
@@ -0,0 +1,55 @@
+/** @file
+  Math worker functions.
+
+  Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
+  This program and the accompanying materials
+  are licensed and made available under the terms and conditions of the BSD License
+  which accompanies this distribution.  The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php.
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
+  WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+
+**/
+
+
+
+
+#include "BaseLibInternals.h"
+
+/**
+  Returns the bit position of the highest bit set in a 64-bit value. Equivalent
+  to log2(x).
+
+  This function computes the bit position of the highest bit set in the 64-bit
+  value specified by Operand. If Operand is zero, then -1 is returned.
+  Otherwise, a value between 0 and 63 is returned.
+
+  @param  Operand The 64-bit operand to evaluate.
+
+  @retval 0..63   Position of the highest bit set in Operand if found.
+  @retval -1      Operand is zero.
+
+**/
+INTN
+EFIAPI
+HighBitSet64 (
+  IN      UINT64                    Operand
+  )
+{
+  if (Operand == (UINT32)Operand) {
+    //
+    // Operand is just a 32-bit integer
+    //
+    return HighBitSet32 ((UINT32)Operand);
+  }
+
+  //
+  // Operand is really a 64-bit integer
+  //
+  if (sizeof (UINTN) == sizeof (UINT32)) {
+    return HighBitSet32 (((UINT32*)&Operand)[1]) + 32;
+  } else {
+    return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
+  }
+}