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 #include "BaseLibInternals.h"
  16
  17 /**
  18   Returns the bit position of the highest bit set in a 32-bit value. Equivalent
  19   to log2(x).
  20
  21   This function computes the bit position of the highest bit set in the 32-bit
  22   value specified by Operand. If Operand is zero, then -1 is returned.
  23   Otherwise, a value between 0 and 31 is returned.
  24
  25   @param  Operand The 32-bit operand to evaluate.
  26
  27   @return Position of the highest bit set in Operand if found.
  28   @retval -1  Operand is zero.
  29
  30 **/
  31 INTN
  32 EFIAPI
  33 HighBitSet32 (
  34   IN      UINT32                    Operand
  35   )
  36 {
  37   INTN                              BitIndex;
  38
  39   if (Operand == 0) {
  40     return - 1;
  41   }
  42   for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1);
  43   return BitIndex;
  44 }