mirror of https://github.com/acidanthera/audk.git
136 lines
3.7 KiB
NASM
136 lines
3.7 KiB
NASM
;/*++
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;
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;Copyright (c) 2006, Intel Corporation
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;All rights reserved. This program and the accompanying materials
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;are licensed and made available under the terms and conditions of the BSD License
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;which accompanies this distribution. The full text of the license may be found at
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;http://opensource.org/licenses/bsd-license.php
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;
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;THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS,
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;WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
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;
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;Module Name:
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;
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; EfiZeroMem.c
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;
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;Abstract:
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;
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; This is the code that supports IA32-optimized ZeroMem service
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;
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;--*/
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;---------------------------------------------------------------------------
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.686
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.model flat,C
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.mmx
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.code
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;---------------------------------------------------------------------------
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;VOID
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;EfiCommonLibZeroMem (
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; IN VOID *Buffer,
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; IN UINTN Count
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; )
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;/*++
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;
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;Input: VOID *Buffer - Pointer to buffer to clear
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; UINTN Count - Number of bytes to clear
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;
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;Output: None.
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;
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;Saves:
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;
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;Modifies:
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;
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;Description: This function is an optimized zero-memory function.
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;
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;Notes: This function tries to zero memory 8 bytes at a time. As a result,
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; it first picks up any misaligned bytes, then words, before getting
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; in the main loop that does the 8-byte clears.
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;
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;--*/
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EfiCommonLibZeroMem PROC
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; UINT64 MmxSave;
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push ebp
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mov ebp, esp
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push ecx ; Reserve space for local variable MmxSave
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push ecx
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push edi
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mov ecx, [ebp + 0Ch] ; Count
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mov edi, [ebp + 8]; Buffer
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; Pick up misaligned start bytes (get pointer 4-byte aligned)
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_StartByteZero:
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mov eax, edi
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and al, 3 ; check lower 2 bits of address
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test al, al
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je _ZeroBlocks ; already aligned?
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cmp ecx, 0
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je _ZeroMemDone
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; Clear the byte memory location
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mov BYTE PTR [edi], 0
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inc edi
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; Decrement our count
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dec ecx
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jmp _StartByteZero ; back to top of loop
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_ZeroBlocks:
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; Compute how many 64-byte blocks we can clear
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mov edx, ecx
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shr ecx, 6 ; convert to 64-byte count
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shl ecx, 6 ; convert back to bytes
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sub edx, ecx ; subtract from the original count
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shr ecx, 6 ; and this is how many 64-byte blocks
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; If no 64-byte blocks, then skip
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cmp ecx, 0
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je _ZeroRemaining
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; Save mm0
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movq [ebp - 8], mm0 ; Save mm0 to MmxSave
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pxor mm0, mm0 ; Clear mm0
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_B:
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movq QWORD PTR ds:[edi], mm0
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movq QWORD PTR ds:[edi+8], mm0
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movq QWORD PTR ds:[edi+16], mm0
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movq QWORD PTR ds:[edi+24], mm0
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movq QWORD PTR ds:[edi+32], mm0
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movq QWORD PTR ds:[edi+40], mm0
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movq QWORD PTR ds:[edi+48], mm0
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movq QWORD PTR ds:[edi+56], mm0
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add edi, 64
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dec ecx
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jnz _B
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; Restore mm0
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movq mm0, [ebp - 8] ; Restore mm0 from MmxSave
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emms ; Exit MMX Instruction
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_ZeroRemaining:
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; Zero out as many DWORDS as possible
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mov ecx, edx
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shr ecx, 2
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xor eax, eax
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rep stosd
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; Zero out remaining as bytes
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mov ecx, edx
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and ecx, 03
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rep stosb
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_ZeroMemDone:
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pop edi
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leave
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ret
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EfiCommonLibZeroMem ENDP
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END
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