MdePkg/Library/BaseLib/HighBitSet64.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 64-bit value. Equivalent
  13   to log2(x).
  14
  15   This function computes the bit position of the highest bit set in the 64-bit
  16   value specified by Operand. If Operand is zero, then -1 is returned.
  17   Otherwise, a value between 0 and 63 is returned.
  18
  19   @param  Operand The 64-bit operand to evaluate.
  20
  21   @retval 0..63   Position of the highest bit set in Operand if found.
  22   @retval -1      Operand is zero.
  23
  24 **/
  25 INTN
  26 EFIAPI
  27 HighBitSet64 (
  28   IN      UINT64  Operand
  29   )
  30 {
  31   if (Operand == (UINT32)Operand) {
  32     //
  33     // Operand is just a 32-bit integer
  34     //
  35     return HighBitSet32 ((UINT32)Operand);
  36   }
  37
  38   //
  39   // Operand is really a 64-bit integer
  40   //
  41   if (sizeof (UINTN) == sizeof (UINT32)) {
  42     return HighBitSet32 (((UINT32 *)&Operand)[1]) + 32;
  43   } else {
  44     return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
  45   }
  46 }