MdePkg/Library/BaseLib/LowBitSet64.c

   1 /** @file
   2   Math worker functions.
   3
   4   Copyright (c) 2006, Intel Corporation<BR>
   5   All rights reserved. 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 // Include common header file for this module.
  17 //
  18
  19
  20 #include "BaseLibInternals.h"
  21
  22 /**
  23   Returns the bit position of the lowest bit set in a 64-bit value.
  24
  25   This function computes the bit position of the lowest bit set in the 64-bit
  26   value specified by Operand. If Operand is zero, then -1 is returned.
  27   Otherwise, a value between 0 and 63 is returned.
  28
  29   @param  Operand The 64-bit operand to evaluate.
  30
  31   @return Position of the lowest bit set in Operand if found.
  32   @retval -1  Operand is zero.
  33
  34 **/
  35 INTN
  36 EFIAPI
  37 LowBitSet64 (
  38   IN      UINT64                    Operand
  39   )
  40 {
  41   INTN                              BitIndex;
  42
  43   if (Operand == 0) {
  44     return -1;
  45   }
  46
  47   for (BitIndex = 0;
  48        (Operand & 1) == 0;
  49        BitIndex++, Operand = RShiftU64 (Operand, 1));
  50   return BitIndex;
  51 }