MdePkg/Library/BaseLib/HighBitSet64.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 64-bit value. Equivalent
  to log2(x).

  This function computes the bit position of the highest bit set in the 64-bit
  value specified by Operand. If Operand is zero, then -1 is returned.
  Otherwise, a value between 0 and 63 is returned.

  @param  Operand The 64-bit operand to evaluate.

  @retval 0..63   Position of the highest bit set in Operand if found.
  @retval -1      Operand is zero.

**/
INTN
EFIAPI
HighBitSet64 (
  IN      UINT64  Operand
  )
{
  if (Operand == (UINT32)Operand) {
    //
    // Operand is just a 32-bit integer
    //
    return HighBitSet32 ((UINT32)Operand);
  }

  //
  // Operand is really a 64-bit integer
  //
  if (sizeof (UINTN) == sizeof (UINT32)) {
    return HighBitSet32 (((UINT32 *)&Operand)[1]) + 32;
  } else {
    return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
  }
}