MdePkg/Library/BaseLib/HighBitSet32.c

   1 /** @file
   2   Math worker functions.
   3
   4   Copyright (c) 2006 - 2008, 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
  17
  18 #include "BaseLibInternals.h"
  19
  20 /**
  21   Returns the bit position of the highest bit set in a 32-bit value. Equivalent
  22   to log2(x).
  23
  24   This function computes the bit position of the highest bit set in the 32-bit
  25   value specified by Operand. If Operand is zero, then -1 is returned.
  26   Otherwise, a value between 0 and 31 is returned.
  27
  28   @param  Operand The 32-bit operand to evaluate.
  29
  30   @retval 0..31  Position of the highest bit set in Operand if found.
  31   @retval -1    Operand is zero.
  32
  33 **/
  34 INTN
  35 EFIAPI
  36 HighBitSet32 (
  37   IN      UINT32                    Operand
  38   )
  39 {
  40   INTN                              BitIndex;
  41
  42   if (Operand == 0) {
  43     return - 1;
  44   }
  45   for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1);
  46   return BitIndex;
  47 }