MdePkg/Library/BaseLib/HighBitSet32.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 #include "CommonHeader.h"
  19
  20 #include "BaseLibInternals.h"
  21
  22 /**
  23   Returns the bit position of the highest bit set in a 32-bit value. Equivalent
  24   to log2(x).
  25
  26   This function computes the bit position of the highest bit set in the 32-bit
  27   value specified by Operand. If Operand is zero, then -1 is returned.
  28   Otherwise, a value between 0 and 31 is returned.
  29
  30   @param  Operand The 32-bit operand to evaluate.
  31
  32   @return Position of the highest bit set in Operand if found.
  33   @retval -1  Operand is zero.
  34
  35 **/
  36 INTN
  37 EFIAPI
  38 HighBitSet32 (
  39   IN      UINT32                    Operand
  40   )
  41 {
  42   INTN                              BitIndex;
  43
  44   if (Operand == 0) {
  45     return - 1;
  46   }
  47   for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1);
  48   return BitIndex;
  49 }