EdkCompatibilityPkg/Foundation/Library/EdkIIGlueLib/Library/BaseLib/HighBitSet32.c

   1 /*++
   2
   3 Copyright (c) 2004 - 2006, Intel Corporation. All rights reserved.<BR>
   4 This program and the accompanying materials
   5 are licensed and made available under the terms and conditions of the BSD License
   6 which accompanies this distribution.  The full text of the license may be found at
   7 http://opensource.org/licenses/bsd-license.php
   8
   9 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  10 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  11
  12
  13 Module Name:
  14
  15   HighBitSet32.c
  16
  17 Abstract:
  18
  19   Math worker functions.
  20
  21 --*/
  22
  23 #include "BaseLibInternals.h"
  24
  25 /**
  26   Returns the bit position of the highest bit set in a 32-bit value. Equivalent
  27   to log2(x).
  28
  29   This function computes the bit position of the highest bit set in the 32-bit
  30   value specified by Operand. If Operand is zero, then -1 is returned.
  31   Otherwise, a value between 0 and 31 is returned.
  32
  33   @param  Operand The 32-bit operand to evaluate.
  34
  35   @return Position of the highest bit set in Operand if found.
  36   @retval -1  Operand is zero.
  37
  38 **/
  39 INTN
  40 EFIAPI
  41 HighBitSet32 (
  42   IN      UINT32                    Operand
  43   )
  44 {
  45   INTN                              BitIndex;
  46
  47   if (Operand == 0) {
  48     return - 1;
  49   }
  50   for (BitIndex = 31; (INT32)Operand > 0; BitIndex--, Operand <<= 1);
  51   return BitIndex;
  52 }