MdePkg/Library/BaseLib/Ia32/RShiftU64.c

/** @file
  64-bit logical right shift function for IA-32

  Copyright (c) 2006 - 2015, Intel Corporation. All rights reserved.<BR>
  SPDX-License-Identifier: BSD-2-Clause-Patent

**/

/**
  Shifts a 64-bit integer right between 0 and 63 bits. This high bits
  are filled with zeros. The shifted value is returned.

  This function shifts the 64-bit value Operand to the right by Count bits. The
  high Count bits are set to zero. The shifted value is returned.

  @param  Operand The 64-bit operand to shift right.
  @param  Count   The number of bits to shift right.

  @return Operand >> Count

**/
UINT64
EFIAPI
InternalMathRShiftU64 (
  IN      UINT64  Operand,
  IN      UINTN   Count
  )
{
  _asm {
    mov     cl, byte ptr [Count]
    xor     edx, edx
    mov     eax, dword ptr [Operand + 4]
    test    cl, 32
    jnz     L0
    mov     edx, eax
    mov     eax, dword ptr [Operand + 0]
L0:
    shrd    eax, edx, cl
    shr     edx, cl
  }
}