evunzip.c

#include <stdio.h>
#include <assert.h>

#include "huffmantree.h"

int main(int argc, char **argv)
{
        int freqs [NUMBER_OF_CHARS] = {0};
        int nchars = 0;
        int code;      
        
        if (argc != 3) {
		perror("error: usage: ./evunzip <source ez file> <destination file>\n");
		return -1;
	}
        char *src_filename = argv[1];
        char *tgt_filename = argv[2];
        
        FILE *src_file = fopen(src_filename, "rb");
	if (src_file == NULL) {
		perror("open_file: could not open file\n");
		return -1;
	}

        /* read headers */
        fread(&code, sizeof(code), 1, src_file);
        assert(code == 0xC0DE);
        fread(freqs, sizeof(freqs[0]), NUMBER_OF_CHARS, src_file);  
        fread(&code, sizeof(code), 1, src_file);
        assert(code == 0xDADA); 
        
        for (int i = 0; i < NUMBER_OF_CHARS; i++)
                nchars += freqs[i];
        
        /* build tree */
        struct treenode *root = build_codes(freqs);

        FILE *tgt_file = fopen(tgt_filename, "wb"); 

        int counter = 0;
        unsigned char code_in = 0;
        struct treenode *t = root;
        while (fread(&code_in, sizeof(code_in), 1, src_file) == 1) {
                for (int i = 1; i <= 8; i++) {
                        /* 8 bits per byte */
                        int bit_position = sizeof(long unsigned int) - 8 + i;
                        unsigned char bit = get_i_bit((long unsigned int) code_in,
                                                      sizeof(code_in) * 8,
                                                      bit_position);
                        t = decode_bit(t, bit);
                        assert(t);
                        if (t->is_leaf) {
                                fwrite(&t->character, sizeof(t->character), 1, tgt_file);
                                counter++;
                                if (counter == nchars)
                                        break;
                                t = root;
                        }
                }
        }
        fclose(src_file);
        fclose(tgt_file);
        destroy_tree(&root);

        return 0;
}