audk/MdePkg/Library/BaseMemoryLibOptDxe/X64/SetMem.S

#------------------------------------------------------------------------------
#
# Copyright (c) 2006 - 2008, Intel Corporation
# All rights reserved. This program and the accompanying materials
# are licensed and made available under the terms and conditions of the BSD License
# which accompanies this distribution.  The full text of the license may be found at
# http://opensource.org/licenses/bsd-license.php
#
# THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
# WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
#
# Module Name:
#
#   SetMem.S
#
# Abstract:
#
#   SetMem function
#
# Notes:
#
#------------------------------------------------------------------------------
#------------------------------------------------------------------------------
#  VOID *
#  EFIAPI
#  InternalMemSetMem (
#    IN VOID   *Buffer,
#    IN UINTN  Count,
#    IN UINT8  Value
#    )
#------------------------------------------------------------------------------
.intel_syntax noprefix
ASM_GLOBAL ASM_PFX(InternalMemSetMem)
ASM_PFX(InternalMemSetMem):
    push    rdi
    push    rbx
    push    rcx         # push Buffer
    mov     rax, r8     # rax = Value
    and     rax, 0xff   # rax = lower 8 bits of r8, upper 56 bits are 0
    mov     ah,  al     # ah  = al
    mov     bx,  ax     # bx  = ax
    shl     rax, 0x10   # rax = ax << 16
    mov     ax,  bx     # ax  = bx
    mov     rbx, rax    # ebx = eax
    shl     rax, 0x20   # rax = rax << 32
    or      rax, rbx    # eax = ebx
    mov     rdi, rcx    # rdi = Buffer
    mov     rcx, rdx    # rcx = Count
    shr     rcx, 3      # rcx = rcx / 8
    cld
    rep     stosq 
    mov     rcx, rdx    # rcx = rdx
    and     rcx, 7      # rcx = rcx & 7
    rep     stosb 
    pop     rax         # rax = Buffer
    pop     rbx
    pop     rdi
    ret