EdkCompatibilityPkg/Foundation/Library/EfiCommonLib/Ia32/RShiftU64.asm

   1 ;/*++
   2 ;
   3 ;Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
   4 ;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 ;  RShiftU64.c
  15 ;
  16 ;Abstract:
  17 ;
  18 ;  64-bit right shift function for IA-32
  19 ;
  20 ;--*/
  21 ;
  22 ;#include "Tiano.h"
  23 ;
  24 ;---------------------------------------------------------------------------
  25     .686
  26     .model  flat,C
  27     .code
  28
  29 ;---------------------------------------------------------------------------
  30 ;UINT64
  31 ;RShiftU64 (
  32 ;  IN UINT64   Operand,
  33 ;  IN UINTN    Count
  34 ;  )
  35 ;/*++
  36 ;
  37 ;Routine Description:
  38 ;  This routine allows a 64 bit value to be right shifted by 32 bits and returns the
  39 ;  shifted value.
  40 ;  Count is valid up 63. (Only Bits 0-5 is valid for Count)
  41 ;Arguments:
  42 ;  Operand - Value to be shifted
  43 ;  Count   - Number of times to shift right.
  44 ;
  45 ;Returns:
  46 ;
  47 ;  Value shifted right identified by the Count.
  48 ;
  49 ;--*/
  50 RShiftU64 PROC
  51
  52     mov    eax, [esp + 4]; dword ptr Operand[0]
  53     mov    edx, [esp + 8]; dword ptr Operand[4]
  54
  55     ;
  56     ; CL is valid from 0 - 31. shld will move EDX:EAX by CL times but EDX is not touched
  57     ; For CL of 32 - 63, it will be shifted 0 - 31 so we will move edx to eax later.
  58     ;
  59     mov    ecx, [esp + 0Ch] ; Count
  60     and    ecx, 63
  61     shrd   eax, edx, cl
  62     shr    edx, cl
  63
  64     cmp    ecx, 32
  65     jc     short _RShiftU64_Done
  66
  67     ;
  68     ; Since Count is 32 - 63, edx will have been shifted  by 0 - 31
  69     ; If shifted by 32 or more, set upper 32 bits to zero.
  70     ;
  71     mov    eax, edx
  72     xor    edx, edx
  73
  74 _RShiftU64_Done:
  75
  76     ret
  77 RShiftU64 ENDP
  78         END