1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
|
/*
* Copyright (c) 2003-2005 The Regents of The University of Michigan
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met: redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer;
* redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution;
* neither the name of the copyright holders nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Authors: Erik Hallnor
*/
/** @file
* LZSSCompression definitions.
*/
#include <cassert>
#include <cstring>
#include "base/compression/lzss_compression.hh"
#include "base/misc.hh" //for fatal
void
LZSSCompression::findSubString(uint8_t *src, int back, int size, uint16_t &L,
uint16_t &P)
{
int front = 0;
int max_length = size - back;
L = 0;
P = back - 1;
while (front < back) {
while (src[front] != src[back] && front < back) ++front;
if (front >= back) {
return;
}
int i = 1;
while (src[front+i] == src[back+i] && i < max_length) ++i;
if (i >= L) {
L = i;
P = front;
}
if (src[front+i] != src[back+i-1]) {
// can't find a longer substring until past this point.
front += i;
} else {
++front;
}
}
}
int
LZSSCompression::emitByte(uint8_t *dest, uint8_t byte)
{
if ((byte >> 5 & 0x7) == 0 || (byte >> 5 & 0x7) == 7) {
// If the top 3 bits are the same, emit 00<6bits>
dest[0] = byte & 0x3f;
return 1;
} else {
// emit 01XXXXXX <8 bits>
dest[0] = 0x40;
dest[1] = byte;
return 2;
}
}
void
LZSSCompression::emitString(uint8_t *dest, uint16_t P, uint16_t L)
{
// Emit 1<7P> <5P><3L> <8L>
dest[0] = 1<<7 | (P >> 5 & 0x7f);
dest[1] = ((P & 0x1f) << 3) | (L>>8 & 0x3);
dest[2] = L & 0xFF;
}
int
LZSSCompression::compress(uint8_t *dest, uint8_t *src, int size)
{
if (size > 4096) {
fatal("Compression can only handle block sizes of 4096 bytes or less");
}
// Encode the first byte.
int dest_index = emitByte(dest, src[0]);
int i = 1;
// A 11 bit field
uint16_t L;
// A 12 bit field
uint16_t P = 0;
while (i < size && dest_index < size) {
L = 0;
if (dest_index+3 >= size) {
dest_index = size;
continue;
}
if (i == size - 1) {
// Output the character
dest_index += emitByte(&dest[dest_index], src[i]);
++i;
continue;
}
findSubString(src, i, size, L, P);
if (L > 1) {
// Output the string reference
emitString(&dest[dest_index], P, L);
dest_index += 3;
i = i+L;
} else {
// Output the character
dest_index += emitByte(&dest[dest_index], src[i]);
++i;
}
}
if (dest_index >= size) {
// Have expansion instead of compression, just copy.
std::memcpy(dest,src,size);
return size;
}
return dest_index;
}
int
LZSSCompression::uncompress(uint8_t *dest, uint8_t *src, int size)
{
int index = 0;
int i = 0;
while (i < size) {
if (src[i] & 1<<7 ) {
// We have a string
// Extract P
int start = (src[i] & 0x3f)<<5 | ((src[i+1] >> 3) & 0x1f);
// Extract L
int len = (src[i+1] & 0x07)<<8 | src[i+2];
i += 3;
for (int j = start; j < start+len; ++j) {
dest[index++] = dest[j];
}
} else {
// We have a character
if (src[i] & 1<<6) {
// Value is in the next byte
dest[index++] = src[i+1];
i += 2;
} else {
// just extend the lower 6 bits
dest[index++] = (src[i] & 0x3f) | ((src[i] & 1<<5) ? 0xC0 : 0);
++i;
}
}
}
return index;
}
|
