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
EfiCommonLibZeroMem(IN VOID * Buffer,IN UINTN Count)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