EdkCompatibilityPkg/Foundation/Library/EfiCommonLib/Ia32/GetPowerOfTwo.c

   1 /*++
   2
   3 Copyright (c) 2006, Intel Corporation
   4 All rights reserved. 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 Module Name:
  13
  14   GetPowerOfTwo.c
  15
  16 Abstract:
  17
  18   Calculates the largest integer that is both
  19   a power of two and less than Input
  20
  21 --*/
  22
  23 #include "Tiano.h"
  24
  25 UINT64
  26 GetPowerOfTwo (
  27   IN UINT64   Input
  28   )
  29 /*++
  30
  31 Routine Description:
  32
  33   Calculates the largest integer that is both
  34   a power of two and less than Input
  35
  36 Arguments:
  37
  38   Input  - value to calculate power of two
  39
  40 Returns:
  41
  42   the largest integer that is both  a power of
  43   two and less than Input
  44
  45 --*/
  46 {
  47   __asm {
  48     xor     eax, eax
  49     mov     edx, eax
  50     mov     ecx, dword ptr Input[4]
  51     jecxz   _F
  52     bsr     ecx, ecx
  53     bts     edx, ecx
  54     jmp     _Exit
  55 _F:
  56     mov     ecx, dword ptr Input[0]
  57     jecxz   _Exit
  58     bsr     ecx, ecx
  59     bts     eax, ecx
  60 _Exit:
  61   }
  62 }