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|
;/*++
;
;Copyright (c) 2006, 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:
;
; EfiZeroMem.c
;
;Abstract:
;
; This is the code that supports IA32-optimized ZeroMem service
;
;--*/
;---------------------------------------------------------------------------
.686
.model flat,C
.mmx
.code
;---------------------------------------------------------------------------
;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.
;
;--*/
EfiCommonLibZeroMem PROC
; UINT64 MmxSave;
push ebp
mov ebp, esp
push ecx ; Reserve space for local variable MmxSave
push ecx
push edi
mov ecx, [ebp + 0Ch] ; Count
mov edi, [ebp + 8]; 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
; Save mm0
movq [ebp - 8], mm0 ; Save mm0 to MmxSave
pxor mm0, mm0 ; Clear mm0
_B:
movq QWORD PTR ds:[edi], mm0
movq QWORD PTR ds:[edi+8], mm0
movq QWORD PTR ds:[edi+16], mm0
movq QWORD PTR ds:[edi+24], mm0
movq QWORD PTR ds:[edi+32], mm0
movq QWORD PTR ds:[edi+40], mm0
movq QWORD PTR ds:[edi+48], mm0
movq QWORD PTR ds:[edi+56], mm0
add edi, 64
dec ecx
jnz _B
; Restore mm0
movq mm0, [ebp - 8] ; Restore mm0 from MmxSave
emms ; Exit MMX Instruction
_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:
pop edi
leave
ret
EfiCommonLibZeroMem ENDP
END
|
