MdePkg/Library/BaseLib/HighBitSet64.c

   1 /** @file
   2   Math worker functions.
   3
   4   Copyright (c) 2006 - 2008, Intel Corporation. All rights reserved.<BR>
   5   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
  17
  18 #include "BaseLibInternals.h"
  19
  20 /**
  21   Returns the bit position of the highest bit set in a 64-bit value. Equivalent
  22   to log2(x).
  23
  24   This function computes the bit position of the highest bit set in the 64-bit
  25   value specified by Operand. If Operand is zero, then -1 is returned.
  26   Otherwise, a value between 0 and 63 is returned.
  27
  28   @param  Operand The 64-bit operand to evaluate.
  29
  30   @retval 0..63   Position of the highest bit set in Operand if found.
  31   @retval -1      Operand is zero.
  32
  33 **/
  34 INTN
  35 EFIAPI
  36 HighBitSet64 (
  37   IN      UINT64                    Operand
  38   )
  39 {
  40   if (Operand == (UINT32)Operand) {
  41     //
  42     // Operand is just a 32-bit integer
  43     //
  44     return HighBitSet32 ((UINT32)Operand);
  45   }
  46
  47   //
  48   // Operand is really a 64-bit integer
  49   //
  50   if (sizeof (UINTN) == sizeof (UINT32)) {
  51     return HighBitSet32 (((UINT32*)&Operand)[1]) + 32;
  52   } else {
  53     return HighBitSet32 ((UINT32)RShiftU64 (Operand, 32)) + 32;
  54   }
  55 }