MdePkg/Library/BaseLib/Ia32/RShiftU64.c

   1 /** @file
   2   64-bit logical right shift function for IA-32
   3
   4   Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
   5   SPDX-License-Identifier: BSD-2-Clause-Patent
   6
   7 **/
   8
   9 /**
  10   Shifts a 64-bit integer right between 0 and 63 bits. This high bits
  11   are filled with zeros. The shifted value is returned.
  12
  13   This function shifts the 64-bit value Operand to the right by Count bits. The
  14   high Count bits are set to zero. The shifted value is returned.
  15
  16   @param  Operand The 64-bit operand to shift right.
  17   @param  Count   The number of bits to shift right.
  18
  19   @return Operand >> Count
  20
  21 **/
  22 UINT64
  23 EFIAPI
  24 InternalMathRShiftU64 (
  25   IN      UINT64  Operand,
  26   IN      UINTN   Count
  27   )
  28 {
  29   _asm {
  30     mov     cl, byte ptr [Count]
  31     xor     edx, edx
  32     mov     eax, dword ptr [Operand + 4]
  33     test    cl, 32
  34     jnz     L0
  35     mov     edx, eax
  36     mov     eax, dword ptr [Operand + 0]
  37 L0:
  38     shrd    eax, edx, cl
  39     shr     edx, cl
  40   }
  41 }