EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/LowBitSet64.c

   1 /*++
   2
   3 Copyright (c) 2004 - 2006, Intel Corporation. All rights reserved.<BR>
   4 This program and the accompanying materials
   5 are licensed and made available under the terms and conditions of the BSD License
   6 which accompanies this distribution.  The full text of the license may be found at
   7 http://opensource.org/licenses/bsd-license.php
   8
   9 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11
  12
  13 Module Name:
  14
  15   LowBitSet64.c
  16
  17 Abstract:
  18
  19   Math worker functions.
  20
  21 --*/
  22
  23 #include "BaseLibInternals.h"
  24
  25 /**
  26   Returns the bit position of the lowest bit set in a 64-bit value.
  27
  28   This function computes the bit position of the lowest bit set in the 64-bit
  29   value specified by Operand. If Operand is zero, then -1 is returned.
  30   Otherwise, a value between 0 and 63 is returned.
  31
  32   @param  Operand The 64-bit operand to evaluate.
  33
  34   @return Position of the lowest bit set in Operand if found.
  35   @retval -1  Operand is zero.
  36
  37 **/
  38 INTN
  39 EFIAPI
  40 LowBitSet64 (
  41   IN      UINT64                    Operand
  42   )
  43 {
  44   INTN                              BitIndex;
  45
  46   if (Operand == 0) {
  47     return -1;
  48   }
  49
  50   for (BitIndex = 0;
  51        (Operand & 1) == 0;
  52        BitIndex++, Operand = RShiftU64 (Operand, 1));
  53   return BitIndex;
  54 }