Category : C Source Code
Archive   : LZW.ZIP
Filename : LZWUNC.C

/* LZWUNC - FILE UNCOMPRESSOR UTILITY */
#include "stdio.h"
#include "debug.h"
#define FALSE 0
#define TRUE !FALSE
#define TABSIZE 4096
#define STACKSIZE TABSIZE
#define NO_PRED 0xFFFF
#define EMPTY 0xF000
#define NOT_FND 0xFFFF
#define NO_UPDATE FALSE
#define UEOF ((unsigned)EOF)

struct entry {
char used;
unsigned int next; /* hi bit is 'used' flag */
unsigned int predecessor; /* 12 bit code */
unsigned char follower;
} string_tab[TABSIZE];

/* routines common to compress and decompress, contained in CommLZW.c */
unsigned hash();
unsigned unhash();
unsigned getcode();
putcode();
init_tab();
upd_tab();

FILE *op; /* global file pointer - gets assigned from outfd so that getch can
determine whether or not to print stuff to the screen */

main(argc,argv)
int argc; char *argv[];
{
register unsigned int c;
int tempc, code, oldcode, incode, finchar,lastchar;
char unknown = FALSE;
int code_count = TABSIZE - 256;
FILE *infd, *outfd;
register struct entry *ep;

if (3 != argc) {
fprintf(stderr,"Usage : lzwunc squeezefilename newfilename\n");
exit(0);
}
if ( -1 == (infd = fopen( *++argv, "r")) ) {
fprintf(stderr,"Cant open %s\n", *argv);
exit(0);
}
if ( -1 == (op = outfd = fopen(*++argv,"w")) ) {
fprintf(stderr,"Cant create %s\n",*argv);
exit(0);
}

init_tab(); /* set up atomic code definitions*/
code = oldcode = getcode(infd);
c = string_tab[code].follower; /* first code always known */
putc(c,outfd);
DEBUGGER(\
putc(c,stderr);\
fprintf(stderr,"\n%x\n",code);\
)
finchar = c;

while ( UEOF != (code = incode = getcode(infd)) ) {
DEBUGGER(fprintf(stderr,"\n%x\n",code);)
ep = &string_tab[code]; /* initialize pointer */
if ( !ep->used )
{ /* if code isn't known */
lastchar = finchar;
code = oldcode;
unknown = TRUE;
ep = &string_tab[code]; /* re-initialize pointer */
}

while (NO_PRED != ep->predecessor)
{
push( ep->follower); /* decode string backwards into */
/* stack */
code = ep->predecessor;
ep = &string_tab[code];
}

finchar = ep->follower;
/* above loop terminates, one way or another, with */
/* string_tab[code].follower = first char in string */

putc(finchar,outfd);
DEBUGGER(putc(finchar,stderr);)
/* pop anything stacked during code parsing */
while ( EMPTY != (tempc = pop()) )
{
putc(tempc,outfd);
DEBUGGER(\
putc(tempc,stderr);\
)
}
if ( unknown ) { /* if code isn't known */
putc(finchar = lastchar,outfd); /* the follower char of last */
unknown = FALSE;
DEBUGGER(\
putc(lastchar,stderr);\
fprintf(stderr,"\nunknown code\n");\
)
}
if ( code_count )
{
upd_tab(oldcode,finchar);
--code_count;
DEBUGGER(fprintf(stderr,"\nAdding %x,%c = %x\n",\
oldcode,finchar,unhash(oldcode,finchar));)
}
oldcode = incode;
}
flushout(outfd); /* write out fractional buffer, if any */
exit(0); /* close all files and quit */
}

char stack[STACKSIZE]; /* stack for pushing and popping characters */
int sp = 0; /* current stack pointer */

push(c)
register int c;
{
stack[sp] = ((char) c);/* coerce passed integer into a character */
++sp;
if (sp >= STACKSIZE) {
fprintf(stderr,"Stack overflow, aborting\n");
exit(1); /* non-0 exit parameter terminates batch job */
}
}

pop()
{
if (sp > 0)
{
--sp; /* push leaves sp pointing to next empty slot */
return ( (int) stack[sp] ); /* make sure pop returns char */
}
else
return EMPTY;
}