audk/EdkCompatibilityPkg/Foundation/Library/EfiCommonLib/Ia32/RShiftU64.c

/*++

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"

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.

--*/
{
  __asm {
  
    mov    eax, dword ptr Operand[0]
    mov    edx, 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, 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:
  }
}