lz77 采用C语音实现
时间: 2023-12-06 14:02:27 浏览: 27
以下是一个简单的LZ77压缩算法的C语言实现:
```
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX_WINDOW_SIZE 4096
#define MAX_LOOKAHEAD_SIZE 18
typedef struct {
int offset;
int length;
char next_char;
} lz77_token;
int search_in_window(char* window, char* lookahead, int window_size, int lookahead_size, lz77_token* token) {
int max_length = 0;
int max_offset = 0;
for (int i = 0; i < window_size; i++) {
int length = 0;
while (lookahead[length] == window[(i + length) % window_size] && length < lookahead_size) {
length++;
}
if (length > max_length) {
max_length = length;
max_offset = i;
}
}
token->offset = max_offset;
token->length = max_length;
token->next_char = lookahead[max_length];
return max_length;
}
void encode(char* input, int input_size, char* output, int* output_size) {
char window[MAX_WINDOW_SIZE];
char lookahead[MAX_LOOKAHEAD_SIZE];
int window_size = 0;
int lookahead_size = 0;
int output_pos = 0;
while (lookahead_size < input_size) {
if (window_size < MAX_WINDOW_SIZE && lookahead_size < MAX_LOOKAHEAD_SIZE) {
window[(window_size + lookahead_size) % MAX_WINDOW_SIZE] = input[lookahead_size];
lookahead[lookahead_size] = input[lookahead_size];
lookahead_size++;
} else {
lz77_token token;
int length = search_in_window(window, lookahead, window_size, lookahead_size, &token);
output[output_pos++] = (char)(token.offset >> 4);
output[output_pos++] = (char)(((token.offset & 0x0F) << 4) | (token.length - 3));
output[output_pos++] = token.next_char;
for (int i = 0; i < length; i++) {
window[(window_size + lookahead_size) % MAX_WINDOW_SIZE] = lookahead[i];
window_size++;
lookahead_size--;
}
}
}
if (lookahead_size > 0) {
lz77_token token;
search_in_window(window, lookahead, window_size, lookahead_size, &token);
output[output_pos++] = (char)(token.offset >> 4);
output[output_pos++] = (char)(((token.offset & 0x0F) << 4) | (token.length - 3));
output[output_pos++] = token.next_char;
}
*output_size = output_pos;
}
void decode(char* input, int input_size, char* output, int* output_size) {
int input_pos = 0;
int output_pos = 0;
while (input_pos < input_size) {
int offset = ((int)input[input_pos] << 4) | ((int)input[input_pos + 1] >> 4);
int length = (input[input_pos + 1] & 0x0F) + 3;
char next_char = input[input_pos + 2];
input_pos += 3;
for (int i = 0; i < length; i++) {
output[output_pos] = output[(output_pos - offset + MAX_WINDOW_SIZE) % MAX_WINDOW_SIZE];
output_pos++;
}
output[output_pos] = next_char;
output_pos++;
}
*output_size = output_pos;
}
int main() {
char input[] = "ababcbababaaaaaa";
int input_size = strlen(input);
char compressed[MAX_WINDOW_SIZE + MAX_LOOKAHEAD_SIZE];
int compressed_size;
encode(input, input_size, compressed, &compressed_size);
printf("Compressed size: %d\n", compressed_size);
for (int i = 0; i < compressed_size; i++) {
printf("%02X ", (unsigned char)compressed[i]);
}
printf("\n");
char decompressed[MAX_WINDOW_SIZE + MAX_LOOKAHEAD_SIZE];
int decompressed_size;
decode(compressed, compressed_size, decompressed, &decompressed_size);
printf("Decompressed size: %d\n", decompressed_size);
for (int i = 0; i < decompressed_size; i++) {
printf("%c", decompressed[i]);
}
printf("\n");
return 0;
}
```
该实现中,`encode`函数将输入字符串压缩成LZ77编码的格式并存储在`output`数组中,`decode`函数将LZ77编码解压缩成原始字符串并存储在`output`数组中。在`main`函数中,我们对输入字符串进行压缩和解压缩,并输出压缩后的大小以及解压缩后的字符串。