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

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