MdePkg/Library/BaseLib/LowBitSet64.c

   1 /** @file
   2   Math worker functions.
   3
   4   Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
   5   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9
  10
  11
  12 #include "BaseLibInternals.h"
  13
  14 /**
  15   Returns the bit position of the lowest bit set in a 64-bit value.
  16
  17   This function computes the bit position of the lowest bit set in the 64-bit
  18   value specified by Operand. If Operand is zero, then -1 is returned.
  19   Otherwise, a value between 0 and 63 is returned.
  20
  21   @param  Operand The 64-bit operand to evaluate.
  22
  23   @retval 0..63  The lowest bit set in Operand was found.
  24   @retval -1     Operand is zero.
  25
  26
  27 **/
  28 INTN
  29 EFIAPI
  30 LowBitSet64 (
  31   IN      UINT64                    Operand
  32   )
  33 {
  34   INTN                              BitIndex;
  35
  36   if (Operand == 0) {
  37     return -1;
  38   }
  39
  40   for (BitIndex = 0;
  41        (Operand & 1) == 0;
  42        BitIndex++, Operand = RShiftU64 (Operand, 1));
  43   return BitIndex;
  44 }