1 /*++ 2 3 Copyright (c) 2006, Intel Corporation. All rights reserved.<BR> 4 This program and the accompanying materials 5 are licensed and made available under the terms and conditions of the BSD License 6 which accompanies this distribution. The full text of the license may be found at 7 http://opensource.org/licenses/bsd-license.php 8 9 THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, 10 WITHOUT WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED. 11 12 Module Name: 13 14 EfiZeroMem.c 15 16 Abstract: 17 18 This is the code that supports IA32-optimized ZeroMem service 19 20 --*/ 21 22 #include "Tiano.h" 23 24 VOID 25 EfiCommonLibZeroMem ( 26 IN VOID *Buffer, 27 IN UINTN Count 28 ) 29 /*++ 30 31 Input: VOID *Buffer - Pointer to buffer to clear 32 UINTN Count - Number of bytes to clear 33 34 Output: None. 35 36 Saves: 37 38 Modifies: 39 40 Description: This function is an optimized zero-memory function. 41 42 Notes: This function tries to zero memory 8 bytes at a time. As a result, 43 it first picks up any misaligned bytes, then words, before getting 44 in the main loop that does the 8-byte clears. 45 46 --*/ 47 { 48 UINT64 MmxSave; 49 __asm { 50 mov ecx, Count 51 mov edi, Buffer 52 53 ; Pick up misaligned start bytes (get pointer 4-byte aligned) 54 _StartByteZero: 55 mov eax, edi 56 and al, 3 ; check lower 2 bits of address 57 test al, al 58 je _ZeroBlocks ; already aligned? 59 cmp ecx, 0 60 je _ZeroMemDone 61 62 ; Clear the byte memory location 63 mov BYTE PTR [edi], 0 64 inc edi 65 66 ; Decrement our count 67 dec ecx 68 jmp _StartByteZero ; back to top of loop 69 70 _ZeroBlocks: 71 72 ; Compute how many 64-byte blocks we can clear 73 mov edx, ecx 74 shr ecx, 6 ; convert to 64-byte count 75 shl ecx, 6 ; convert back to bytes 76 sub edx, ecx ; subtract from the original count 77 shr ecx, 6 ; and this is how many 64-byte blocks 78 79 ; If no 64-byte blocks, then skip 80 cmp ecx, 0 81 je _ZeroRemaining 82 83 ; Save mm0 84 movq MmxSave, mm0 85 86 pxor mm0, mm0 ; Clear mm0 87 88 _B: 89 movq QWORD PTR ds:[edi], mm0 90 movq QWORD PTR ds:[edi+8], mm0 91 movq QWORD PTR ds:[edi+16], mm0 92 movq QWORD PTR ds:[edi+24], mm0 93 movq QWORD PTR ds:[edi+32], mm0 94 movq QWORD PTR ds:[edi+40], mm0 95 movq QWORD PTR ds:[edi+48], mm0 96 movq QWORD PTR ds:[edi+56], mm0 97 98 add edi, 64 99 dec ecx 100 jnz _B 101 102 ; Restore mm0 103 movq mm0, MmxSave 104 emms ; Exit MMX Instruction 105 106 _ZeroRemaining: 107 ; Zero out as many DWORDS as possible 108 mov ecx, edx 109 shr ecx, 2 110 xor eax, eax 111 112 rep stosd 113 114 ; Zero out remaining as bytes 115 mov ecx, edx 116 and ecx, 03 117 118 rep stosb 119 120 _ZeroMemDone: 121 } 122 } 123
