141 lines
3.2 KiB
C
141 lines
3.2 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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#define WSIZE 250
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#define BSIZE 50
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typedef struct {
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unsigned char pos;
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unsigned char n;
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char symb;
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} LZ77Token;
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int compress_1(const char* input_file, const char* output_file)
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{
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int compr_size = 0;
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FILE* input = fopen(input_file, "rb");
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FILE* output = fopen(output_file, "wb");
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if (!input || !output)
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{
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exit(-1);
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}
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char window[WSIZE] = { 0 };
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char buffer[BSIZE] = { 0 };
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int w_start = 0;
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int w_end = 0;
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while (!feof(input))
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{
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int blen = fread(buffer, 1, BSIZE, input);
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for (int bpos = 0; bpos < blen; ++bpos)
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{
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int best_pos = 0;
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int best_n = 0;
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for (int spos = w_start; spos < w_end; ++spos)
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{
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int mlength = 0;
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while (mlength < blen - bpos &&
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mlength < WSIZE &&
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(spos + mlength) < w_end &&
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window[(spos + mlength) % WSIZE] == buffer[bpos + mlength])
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{
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++mlength;
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}
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if (mlength > best_n)
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{
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best_pos = w_end - spos;
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best_n = mlength;
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}
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}
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LZ77Token token;
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token.pos = best_pos;
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token.n = best_n;
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if (bpos + best_n < blen)
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{
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token.symb = buffer[bpos + best_n];
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}
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else
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{
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token.symb = '\0';
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}
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sz=fwrite(&token, sizeof(LZ77Token), 1, output);
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compr_size += sizeof(LZ77Token) * sz;
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for (int j = 0; j <= best_n && bpos < blen; ++j)
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{
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if (bpos + j < blen)
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{
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window[w_end % WSIZE] = buffer[bpos + j];
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w_end++;
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if (w_end - w_start > WSIZE)
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{
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w_start++;
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}
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}
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}
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bpos += best_n;
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}
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}
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fclose(input);
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fclose(output);
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return compr_size;
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}
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int decompress_1(const char* input_file, const char* output_file)
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{
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int compr_size = 0, sz = 0;
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FILE* input = fopen(input_file, "rb");
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FILE* output = fopen(output_file, "wb");
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if (!input || !output)
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{
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exit(-1);
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}
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char window[WSIZE] = { 0 };
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int window_end = 0;
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LZ77Token token;
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while (fread(&token, sizeof(LZ77Token), 1, input))
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{
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if (token.pos == 0 && token.n == 0 && token.symb == '\0')
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{
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continue;
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}
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int start_index = (window_end - token.pos + WSIZE) % WSIZE;
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for (int i = 0; i < token.n; ++i)
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{
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char ch = window[(start_index + i) % WSIZE];
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compr_size += fwrite(&ch, 1, 1, output);
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window[window_end % WSIZE] = ch;
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window_end = (window_end + 1) % WSIZE;
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}
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if (token.symb != '\0')
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{
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compr_size += fwrite(&token.symb, 1, 1, output);
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window[window_end % WSIZE] = token.symb;
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window_end = (window_end + 1) % WSIZE;
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}
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}
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fclose(input);
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fclose(output);
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return compr_size;
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}
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