EdkCompatibilityPkg/Foundation/Library/EfiCommonLib/Ia32/RShiftU64.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:
;
;  RShiftU64.c
;
;Abstract:
;
;  64-bit right shift function for IA-32
;
;--*/
;
;#include "Tiano.h"
;
;---------------------------------------------------------------------------
    .686
    .model  flat,C
    .code

;---------------------------------------------------------------------------
;UINT64
;RShiftU64 (
;  IN UINT64   Operand,
;  IN UINTN    Count
;  )
;/*++
;
;Routine Description:
;  This routine allows a 64 bit value to be right shifted by 32 bits and returns the 
;  shifted value.
;  Count is valid up 63. (Only Bits 0-5 is valid for Count)
;Arguments:
;  Operand - Value to be shifted
;  Count   - Number of times to shift right.
; 
;Returns:
;
;  Value shifted right identified by the Count.
;
;--*/
RShiftU64 PROC
  
    mov    eax, [esp + 4]; dword ptr Operand[0]
    mov    edx, [esp + 8]; dword ptr Operand[4]
  
    ;
    ; CL is valid from 0 - 31. shld will move EDX:EAX by CL times but EDX is not touched
    ; For CL of 32 - 63, it will be shifted 0 - 31 so we will move edx to eax later. 
    ;
    mov    ecx, [esp + 0Ch] ; Count
    and    ecx, 63
    shrd   eax, edx, cl
    shr    edx, cl

    cmp    ecx, 32
    jc     short _RShiftU64_Done

    ;
    ; Since Count is 32 - 63, edx will have been shifted  by 0 - 31                                                     
    ; If shifted by 32 or more, set upper 32 bits to zero.
    ;
    mov    eax, edx
    xor    edx, edx

_RShiftU64_Done:

    ret
RShiftU64 ENDP	
	END