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
  10
  11
  12 #include "BaseLibInternals.h"
  13
  14 /**
  15   Returns the bit position of the highest bit set in a 64-bit value. Equivalent
  16   to log2(x).
  17
  18   This function computes the bit position of the highest bit set in the 64-bit
  19   value specified by Operand. If Operand is zero, then -1 is returned.
  20   Otherwise, a value between 0 and 63 is returned.
  21
  22   @param  Operand The 64-bit operand to evaluate.
  23
  24   @retval 0..63   Position of the highest bit set in Operand if found.
  25   @retval -1      Operand is zero.
  26
  27 **/
  28 INTN
  29 EFIAPI
  30 HighBitSet64 (
  31   IN      UINT64                    Operand
  32   )
  33 {
  34   if (Operand == (UINT32)Operand) {
  35     //
  36     // Operand is just a 32-bit integer
  37     //
  38     return HighBitSet32 ((UINT32)Operand);
  39   }
  40
  41   //
  42   // Operand is really a 64-bit integer
  43   //
  44   if (sizeof (UINTN) == sizeof (UINT32)) {
  45     return HighBitSet32 (((UINT32*)&Operand)[1]) + 32;
  46   } else {
  47     return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
  48   }
  49 }