MdePkg/Library/BaseLib/HighBitSet32.c

/** @file
  Math worker functions.

  Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

#include "BaseLibInternals.h"

/**
  Returns the bit position of the highest bit set in a 32-bit value. Equivalent
  to log2(x).

  This function computes the bit position of the highest bit set in the 32-bit
  value specified by Operand. If Operand is zero, then -1 is returned.
  Otherwise, a value between 0 and 31 is returned.

  @param  Operand The 32-bit operand to evaluate.

  @retval 0..31  Position of the highest bit set in Operand if found.
  @retval -1     Operand is zero.

**/
INTN
EFIAPI
HighBitSet32 (
  IN      UINT32  Operand
  )
{
  INTN  BitIndex;

  if (Operand == 0) {
    return -1;
  }

  for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1) {
  }

  return BitIndex;
}