audk/EdkCompatibilityPkg/Foundation/Library/EfiCommonLib/Ia32/EfiZeroMemSSE2.c

/*++

Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
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:

  EfiZeroMemSSE2.c

Abstract:

  This is the code that supports IA32-optimized ZeroMem service

--*/

#include "Tiano.h"

VOID
EfiCommonLibZeroMem (
  IN VOID   *Buffer,
  IN UINTN  Count
  )
/*++

Input:  VOID   *Buffer - Pointer to buffer to clear
        UINTN  Count  - Number of bytes to clear

Output: None.

Saves:

Modifies:

Description:  This function is an optimized zero-memory function.

Notes:  This function tries to zero memory 8 bytes at a time. As a result, 
        it first picks up any misaligned bytes, then words, before getting 
        in the main loop that does the 8-byte clears.

--*/
{
  __asm {
  mov   ecx, Count
  mov   edi, Buffer

  ; Pick up misaligned start bytes (get pointer 4-byte aligned)
_StartByteZero:
  mov   eax, edi    
  and   al, 3                       ; check lower 2 bits of address
  test  al, al
  je    _ZeroBlocks                 ; already aligned?
  cmp   ecx, 0
  je    _ZeroMemDone

  ; Clear the byte memory location
  mov   BYTE PTR [edi], 0           
  inc    edi

  ; Decrement our count
  dec    ecx
  jmp   _StartByteZero        ; back to top of loop

_ZeroBlocks:

  ; Compute how many 64-byte blocks we can clear 
  mov   edx, ecx
  shr   ecx, 6                      ; convert to 64-byte count
  shl   ecx, 6                      ; convert back to bytes
  sub   edx, ecx                    ; subtract from the original count
  shr   ecx, 6                      ; and this is how many 64-byte blocks

  ; If no 64-byte blocks, then skip 
  cmp    ecx, 0
  je    _ZeroRemaining

  xorps  xmm1, xmm1

_B:
  movdqu OWORD PTR ds:[edi], xmm1
  movdqu OWORD PTR ds:[edi+16], xmm1
  movdqu OWORD PTR ds:[edi+32], xmm1
  movdqu OWORD PTR ds:[edi+48], xmm1
   
  add    edi, 64
  dec    ecx
  jnz    _B
  

_ZeroRemaining:
  ; Zero out as many DWORDS as possible
  mov   ecx, edx
  shr   ecx, 2
  xor   eax, eax

  rep stosd

  ; Zero out remaining as bytes
  mov   ecx, edx
  and   ecx, 03

  rep   stosb
 
_ZeroMemDone:
  }
}