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 #include "BaseLibInternals.h"
  10
  11 /**
  12   Returns the bit position of the lowest bit set in a 64-bit value.
  13
  14   This function computes the bit position of the lowest bit set in the 64-bit
  15   value specified by Operand. If Operand is zero, then -1 is returned.
  16   Otherwise, a value between 0 and 63 is returned.
  17
  18   @param  Operand The 64-bit operand to evaluate.
  19
  20   @retval 0..63  The lowest bit set in Operand was found.
  21   @retval -1     Operand is zero.
  22
  23
  24 **/
  25 INTN
  26 EFIAPI
  27 LowBitSet64 (
  28   IN      UINT64  Operand
  29   )
  30 {
  31   INTN  BitIndex;
  32
  33   if (Operand == 0) {
  34     return -1;
  35   }
  36
  37   for (BitIndex = 0;
  38        (Operand & 1) == 0;
  39        BitIndex++, Operand = RShiftU64 (Operand, 1))
  40   {
  41   }
  42
  43   return BitIndex;
  44 }