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

   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     .686
  24     .model  flat,C
  25     .code
  26
  27 ;---------------------------------------------------------------------------
  28
  29 ;UINT64
  30 ;GetPowerOfTwo (
  31 ;  IN UINT64   Input
  32 ;  )
  33 ;/*++
  34 ;
  35 ;Routine Description:
  36 ;
  37 ;  Calculates the largest integer that is both
  38 ;  a power of two and less than Input
  39 ;
  40 ;Arguments:
  41 ;
  42 ;  Input  - value to calculate power of two
  43 ;
  44 ;Returns:
  45 ;
  46 ;  the largest integer that is both  a power of
  47 ;  two and less than Input
  48 ;
  49 ;--*/
  50 GetPowerOfTwo PROC
  51     xor     eax, eax
  52     mov     edx, eax
  53     mov     ecx, [esp + 8] ; dword ptr Input[4]
  54     jecxz   _F
  55     bsr     ecx, ecx
  56     bts     edx, ecx
  57     jmp     _Exit
  58 _F:
  59     mov     ecx, [esp + 4] ; dword ptr Input[0]
  60     jecxz   _Exit
  61     bsr     ecx, ecx
  62     bts     eax, ecx
  63 _Exit:
  64
  65     ret
  66 GetPowerOfTwo  ENDP
  67         END