-
Notifications
You must be signed in to change notification settings - Fork 0
/
LZ77.cpp
173 lines (125 loc) · 4.38 KB
/
LZ77.cpp
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
//
// Created by Fedor on 31.03.2020.
//
#include "LZ77.h"
LZ77::Node *LZ77::findMatching(const string& vocab_buffer, int vocab_buffer_end, string preview_buffer,
int preview_buffer_end)
{
unsigned short position = 0, length = 0;
unsigned short buffer_pos = 0;
string buffer_reversed = vocab_buffer.substr(0, vocab_buffer_end + 1);
string buffer ="";
for (size_t i = 0; i < buffer_reversed.length(); i++)
{
buffer += buffer_reversed[buffer_reversed.length() - i - 1];
}
buffer += preview_buffer.substr(0, preview_buffer_end + 1);
for (int i = 1; i <= preview_buffer_end + 1; i++)
{
buffer_pos = buffer.find(preview_buffer.substr(0, i));
if (buffer_pos == vocab_buffer_end + 1) break;
else
{
position = vocab_buffer_end - buffer_pos + 1;
length = i;
}
}
byte symbol;
if (position + length == 0)
{
symbol = preview_buffer[0];
}
else
{
symbol = buffer[buffer_pos + length];
}
Node* node = new Node(position, length, symbol);
return node;
}
vector<byte> LZ77::Encode(vector<byte> input, int VOCAB_BUFFER_SIZE, int PREVIEW_BUFFER_SIZE)
{
string vocab_buffer;
string preview_buffer;
int vocab_buffer_end = -1;
int preview_buffer_end = min(PREVIEW_BUFFER_SIZE, (int) input.size()) - 1;
vector<Node*> nodes;
int input_pointer = input.size() > PREVIEW_BUFFER_SIZE ? PREVIEW_BUFFER_SIZE : -1;
for (int i = 0; i <= preview_buffer_end; i++)
{
preview_buffer.push_back(input[i]);
}
while (preview_buffer_end >= 0)
{
nodes.push_back(findMatching(vocab_buffer, vocab_buffer_end, preview_buffer, preview_buffer_end));
for (int i = 0; i < nodes.back()->length + 1; i++)
{
if (vocab_buffer_end >= VOCAB_BUFFER_SIZE - 1)
{
vocab_buffer.pop_back();
vocab_buffer_end--;
}
vocab_buffer.insert(vocab_buffer.begin(), preview_buffer[i]);
vocab_buffer_end++;
}
preview_buffer.erase(0, nodes.back()->length + 1);
preview_buffer_end -= nodes.back()->length + 1;
while (preview_buffer_end < PREVIEW_BUFFER_SIZE - 1 && input_pointer > 0 && input_pointer < input.size())
{
preview_buffer.push_back(input[input_pointer]);
preview_buffer_end++;
input_pointer++;
}
}
vector<byte>output;
LongShortByteUnion longShortByteUnion;
output.push_back(input.size() % 10);
for (size_t i = 0; i < nodes.size(); i++)
{
// Position, 2 bytes
longShortByteUnion.uShort = nodes[i]->position;
output.push_back(longShortByteUnion.uBytes[1]);
output.push_back(longShortByteUnion.uBytes[0]);
// Length, 2 bytes
longShortByteUnion.uShort = nodes[i]->length;
output.push_back(longShortByteUnion.uBytes[1]);
output.push_back(longShortByteUnion.uBytes[0]);
// Symbol, 1 byte
output.push_back(nodes[i]->symbol);
}
return output;
}
vector<byte> LZ77::Decode(vector<byte> input)
{
LongShortByteUnion longShortByteUnion;
vector<Node*> nodes;
byte fileSizeLastDigit = input[0];
input.erase(input.begin());
for (unsigned long long i = 0; i < input.size(); i += SYMBOL_DATA_SIZE)
{
longShortByteUnion.uBytes[1] = input[i];
longShortByteUnion.uBytes[0] = input[i + 1];
unsigned short position = longShortByteUnion.uShort;
longShortByteUnion.uBytes[1] = input[i + 2];
longShortByteUnion.uBytes[0] = input[i + 3];
unsigned short length = longShortByteUnion.uShort;
nodes.push_back(new Node(position, length, input[i + 4]));
}
string result = "";
for (size_t i = 0; i < nodes.size(); i++)
{
int str_length = result.length();
int index = str_length - nodes[i]->position;
int counter = 0;
while (counter < nodes[i]->length)
{
if (index >= str_length) index = str_length - nodes[i]->position;
result += result[index];
index++;
counter++;
}
result += nodes[i]->symbol;
}
vector<byte> output(result.begin(), result.size() % 10 == (fileSizeLastDigit + 1) % 10 ?
result.end() - 1 : result.end());
return output;
}