MdePkg/Library/BaseLib/Ia32/RShiftU64.c

   1 /** @file
   2   64-bit logical right shift function for IA-32
   3
   4   Copyright (c) 2006 - 2007, Intel Corporation<BR>
   5   All rights reserved. This program and the accompanying materials
   6   are licensed and made available under the terms and conditions of the BSD License
   7   which accompanies this distribution.  The full text of the license may be found at
   8   http://opensource.org/licenses/bsd-license.php
   9
  10   THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
  11   WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
  12
  13 **/
  14
  15 //
  16 // Include common header file for this module.
  17 //
  18
  19
  20 /**
  21   Shifts a 64-bit integer right between 0 and 63 bits. This high bits
  22   are filled with zeros. The shifted value is returned.
  23
  24   This function shifts the 64-bit value Operand to the right by Count bits. The
  25   high Count bits are set to zero. The shifted value is returned.
  26
  27   @param  Operand The 64-bit operand to shift right.
  28   @param  Count   The number of bits to shift right.
  29
  30   @return Operand >> Count
  31
  32 **/
  33 UINT64
  34 EFIAPI
  35 InternalMathRShiftU64 (
  36   IN      UINT64                    Operand,
  37   IN      UINTN                     Count
  38   )
  39 {
  40   _asm {
  41     mov     cl, byte ptr [Count]
  42     xor     edx, edx
  43     mov     eax, dword ptr [Operand + 4]
  44     test    cl, 32
  45     cmovz   edx, eax
  46     cmovz   eax, dword ptr [Operand + 0]
  47     shrd    eax, edx, cl
  48     shr     edx, cl
  49   }
  50 }
  51