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

;/*++
;
;Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
;This program and the accompanying materials                          
;are licensed and made available under the terms and conditions of the BSD License         
;which accompanies this distribution.  The full text of the license may be found at        
;http://opensource.org/licenses/bsd-license.php                                            
;                                                                                          
;THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,                     
;WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.             
;
;Module Name:
;
;  GetPowerOfTwo.c
;
;Abstract:
;
;  Calculates the largest integer that is both 
;  a power of two and less than Input
;
;--*/
;---------------------------------------------------------------------------
    .686
    .model  flat,C
    .code

;---------------------------------------------------------------------------

;UINT64
;GetPowerOfTwo (
;  IN UINT64   Input
;  )
;/*++
;
;Routine Description:
;
;  Calculates the largest integer that is both 
;  a power of two and less than Input
;
;Arguments:
;
;  Input  - value to calculate power of two
;
;Returns:
;
;  the largest integer that is both  a power of 
;  two and less than Input
;
;--*/
GetPowerOfTwo PROC
    xor     eax, eax
    mov     edx, eax
    mov     ecx, [esp + 8] ; dword ptr Input[4]
    jecxz   _F
    bsr     ecx, ecx
    bts     edx, ecx
    jmp     _Exit
_F:
    mov     ecx, [esp + 4] ; dword ptr Input[0]
    jecxz   _Exit
    bsr     ecx, ecx
    bts     eax, ecx
_Exit:

    ret
GetPowerOfTwo  ENDP
	END