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