Added to support X64 port (with SV5 ABI). May be able to remove after we port everything, but Sec, to EFI X64 ABI.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@10683 6f19259b-4bc3-4df7-8a09-765794883524

UnixPkg/Library/UnixBaseLib/LowBitSet64.c

@@ -0,0 +1,50 @@
+/** @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 lowest bit set in a 64-bit value.
+
+  This function computes the bit position of the lowest 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  The lowest bit set in Operand was found.
+  @retval -1     Operand is zero.
+
+
+**/
+INTN
+EFIAPI
+LowBitSet64 (
+  IN      UINT64                    Operand
+  )
+{
+  INTN                              BitIndex;
+
+  if (Operand == 0) {
+    return -1;
+  }
+
+  for (BitIndex = 0;
+       (Operand & 1) == 0;
+       BitIndex++, Operand = RShiftU64 (Operand, 1));
+  return BitIndex;
+}