MdePkg/Library/BaseLib/HighBitSet64.c

   1 /** @file
   2   Math worker functions.
   3
   4   Copyright (c) 2006, Intel Corporation<BR>
   5   All rights reserved. This program and the accompanying materials
   6   are licensed and made available under the terms and conditions of the BSD License
   7   which accompanies this distribution.  The full text of the license may be found at
   8   http://opensource.org/licenses/bsd-license.php
   9
  10   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12
  13 **/
  14
  15 //
  16 // Include common header file for this module.
  17 //
  18 #include "CommonHeader.h"
  19
  20 #include "BaseLibInternals.h"
  21
  22 /**
  23   Returns the bit position of the highest bit set in a 64-bit value. Equivalent
  24   to log2(x).
  25
  26   This function computes the bit position of the highest bit set in the 64-bit
  27   value specified by Operand. If Operand is zero, then -1 is returned.
  28   Otherwise, a value between 0 and 63 is returned.
  29
  30   @param  Operand The 64-bit operand to evaluate.
  31
  32   @return Position of the highest bit set in Operand if found.
  33   @retval -1  Operand is zero.
  34
  35 **/
  36 INTN
  37 EFIAPI
  38 HighBitSet64 (
  39   IN      UINT64                    Operand
  40   )
  41 {
  42   if (Operand == (UINT32)Operand) {
  43     //
  44     // Operand is just a 32-bit integer
  45     //
  46     return HighBitSet32 ((UINT32)Operand);
  47   }
  48
  49   //
  50   // Operand is really a 64-bit integer
  51   //
  52   if (sizeof (UINTN) == sizeof (UINT32)) {
  53     return HighBitSet32 (((UINT32*)&Operand)[1]) + 32;
  54   } else {
  55     return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
  56   }
  57 }