MdePkg/Library/BaseLib/HighBitSet32.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
  10
  11
  12 #include "BaseLibInternals.h"
  13
  14 /**
  15   Returns the bit position of the highest bit set in a 32-bit value. Equivalent
  16   to log2(x).
  17
  18   This function computes the bit position of the highest bit set in the 32-bit
  19   value specified by Operand. If Operand is zero, then -1 is returned.
  20   Otherwise, a value between 0 and 31 is returned.
  21
  22   @param  Operand The 32-bit operand to evaluate.
  23
  24   @retval 0..31  Position of the highest bit set in Operand if found.
  25   @retval -1     Operand is zero.
  26
  27 **/
  28 INTN
  29 EFIAPI
  30 HighBitSet32 (
  31   IN      UINT32                    Operand
  32   )
  33 {
  34   INTN                              BitIndex;
  35
  36   if (Operand == 0) {
  37     return - 1;
  38   }
  39   for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1);
  40   return BitIndex;
  41 }