lzw.c

LZW压缩和解压缩程序 lzw.c 主要的功能模块 bitio.c/bitio.h 一些支撑函数

/*
 * Definition for LZW coding 
 *
 * vim: ts=4 sw=4 cindent nowrap
 */
#include <stdlib.h>
#include <stdio.h>
#include "bitio.h"
#define MAX_CODE 65535

struct {
	int suffix;
	int parent, firstchild, nextsibling;
} dictionary[MAX_CODE+1];
int next_code;
int d_stack[MAX_CODE]; // stack for decoding a phrase

#define input(f) ((int)BitsInput( f, 16))
#define output(f, x) BitsOutput( f, (unsigned long)(x), 16)

int DecodeString( int start, int code);
void InitDictionary( void);
void PrintDictionary( void){
	int n;
	int count;
	for( n=256; n<next_code; n++){
		count = DecodeString( 0, n);
		printf( "%4d->", n);
		while( 0<count--) printf("%c", (char)(d_stack[count]));
		printf( "\n");
	}
}

int DecodeString( int start, int code){
	int count;
	count = start;
	while( 0<=code){
		d_stack[ count] = dictionary[code].suffix;
		code = dictionary[code].parent;
		count ++;
	}
	return count;
}
void InitDictionary( void){
	int i;

	for( i=0; i<256; i++){
		dictionary[i].suffix = i;
		dictionary[i].parent = -1;
		dictionary[i].firstchild = -1;
		dictionary[i].nextsibling = i+1;
	}
	dictionary[255].nextsibling = -1;
	next_code = 256;
}
/*
 * Input: string represented by string_code in dictionary,
 * Output: the index of character+string in the dictionary
 * 		index = -1 if not found
 */
int InDictionary( int character, int string_code){
	int sibling;
	if( 0>string_code) return character;
	sibling = dictionary[string_code].firstchild;
	while( -1<sibling){
		if( character == dictionary[sibling].suffix) return sibling;
		sibling = dictionary[sibling].nextsibling;
	}
	return -1;
}

void AddToDictionary( int character, int string_code){
	int firstsibling, nextsibling;
	if( 0>string_code) return;
	dictionary[next_code].suffix = character;
	dictionary[next_code].parent = string_code;
	dictionary[next_code].nextsibling = -1;
	dictionary[next_code].firstchild = -1;
	firstsibling = dictionary[string_code].firstchild;
	if( -1<firstsibling){	// the parent has child
		nextsibling = firstsibling;
		while( -1<dictionary[nextsibling].nextsibling ) 
			nextsibling = dictionary[nextsibling].nextsibling;
		dictionary[nextsibling].nextsibling = next_code;
	}else{// no child before, modify it to be the first
		dictionary[string_code].firstchild = next_code;
	}
	next_code ++;
}

void LZWEncode( FILE *fp, BITFILE *bf){
	int character;
	int string_code;
	int index;
	unsigned long file_length;

	fseek( fp, 0, SEEK_END);
	file_length = ftell( fp);
	fseek( fp, 0, SEEK_SET);
	BitsOutput( bf, file_length, 4*8);
	InitDictionary();
	string_code = -1;
	while( EOF!=(character=fgetc( fp))){
		index = InDictionary( character, string_code);
		if( 0<=index){	// string+character in dictionary
			string_code = index;
		}else{	// string+character not in dictionary
			output( bf, string_code);
			if( MAX_CODE > next_code){	// free space in dictionary
				// add string+character to dictionary
				AddToDictionary( character, string_code);
			}
			string_code = character;
		}
	}
	output( bf, string_code);
}

void LZWDecode( BITFILE *bf, FILE *fp){
	int character;
	int new_code, last_code;
	int phrase_length;
	unsigned long file_length;

	file_length = BitsInput( bf, 4*8);
	if( -1 == file_length) file_length = 0;
	InitDictionary();
	last_code = -1;
	while( 0<file_length){
		new_code = input( bf);
		if( new_code >= next_code){ // this is the case CSCSC( not in dict)
			d_stack[0] = character;
			phrase_length = DecodeString( 1, last_code);
		}else{
			phrase_length = DecodeString( 0, new_code);
		}
		character = d_stack[phrase_length-1];
		while( 0<phrase_length){
			phrase_length --;
			fputc( d_stack[ phrase_length], fp);
			file_length--;
		}
		if( MAX_CODE>next_code){	// add the new phrase to dictionary
			AddToDictionary( character, last_code);
		}
		last_code = new_code;
	}
}



int main( int argc, char **argv){
	FILE *fp;
	BITFILE *bf;

	if( 4>argc){
		fprintf( stdout, "usage: \n%s <o> <ifile> <ofile>\n", argv[0]);
		fprintf( stdout, "\t<o>: E or D reffers encode or decode\n");
		fprintf( stdout, "\t<ifile>: input file name\n");
		fprintf( stdout, "\t<ofile>: output file name\n");
		return -1;
	}
	if( 'E' == argv[1][0]){ // do encoding
		fp = fopen( argv[2], "rb");
		bf = OpenBitFileOutput( argv[3]);
		if( NULL!=fp && NULL!=bf){
			LZWEncode( fp, bf);
			fclose( fp);
			CloseBitFileOutput( bf);
			fprintf( stdout, "encoding done\n");
		}
	}else if( 'D' == argv[1][0]){	// do decoding
		bf = OpenBitFileInput( argv[2]);
		fp = fopen( argv[3], "wb");
		if( NULL!=fp && NULL!=bf){
			LZWDecode( bf, fp);
			fclose( fp);
			CloseBitFileInput( bf);
			fprintf( stdout, "decoding done\n");
		}
	}else{	// otherwise
		fprintf( stderr, "not supported operation\n");
	}
	return 0;
}