MdePkg/Library/BaseLib/LowBitSet64.c

   1 /** @file
   2   Math worker functions.
   3
   4   Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
   5   This program and the accompanying materials
   6   are licensed and made available under the terms and conditions of the BSD License
   7   which accompanies this distribution.  The full text of the license may be found at
   8   http://opensource.org/licenses/bsd-license.php
   9
  10   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12
  13 **/
  14
  15
  16
  17
  18 #include "BaseLibInternals.h"
  19
  20 /**
  21   Returns the bit position of the lowest bit set in a 64-bit value.
  22
  23   This function computes the bit position of the lowest bit set in the 64-bit
  24   value specified by Operand. If Operand is zero, then -1 is returned.
  25   Otherwise, a value between 0 and 63 is returned.
  26
  27   @param  Operand The 64-bit operand to evaluate.
  28
  29   @retval 0..63  The lowest bit set in Operand was found.
  30   @retval -1    Operand is zero.
  31
  32
  33 **/
  34 INTN
  35 EFIAPI
  36 LowBitSet64 (
  37   IN      UINT64                    Operand
  38   )
  39 {
  40   INTN                              BitIndex;
  41
  42   if (Operand == 0) {
  43     return -1;
  44   }
  45
  46   for (BitIndex = 0;
  47        (Operand & 1) == 0;
  48        BitIndex++, Operand = RShiftU64 (Operand, 1));
  49   return BitIndex;
  50 }