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TITLE EfiZeroMem.asm: Optimized memory-zero routine
;------------------------------------------------------------------------------
;
; Copyright (c) 2004, 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.asm
;
; Abstract:
;
; This is the code that supports IA32-optimized ZeroMem service
;
;------------------------------------------------------------------------------
; PROC:PRIVATE
.686P
.MMX
.MODEL SMALL
.CODE
EfiCommonLibZeroMem PROTO C Buffer:PTR DWORD, Count:DWORD
;------------------------------------------------------------------------------
; Procedure: EfiCommonLibZeroMem
;
; 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 C Buffer:PTR DWORD, Count:DWORD
LOCAL MmxSave:QWORD
; Save edi, then put the buffer pointer into it.
push edi
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
; Save mm0
movq MmxSave, mm0
pxor mm0, mm0 ; Clear mm0
@@:
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, 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
ret
EfiCommonLibZeroMem ENDP
END
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