/* LZWUNC - FILE UNCOMPRESSOR UTILITY					*/
#include "stdio.h"
#include "fcntl.h"
#include "sgtty.h"
#define FALSE    0
#define TRUE     !FALSE
#define TABSIZE  4096
#define STACKSIZE TABSIZE
#define NO_PRED  -1
#define EMPTY    -1
#define NOT_FND  -1
#define NO_UPDATE FALSE
struct entry {
  char used;
  int next;		/* hi bit is 'used' flag			*/
  int predecessor;			/* 12 bit code			*/
  char follower;
} string_tab[TABSIZE];

char is_a_con = FALSE;	/* suppresses printing dots during operation if
			   outfd is the console				*/

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

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

  if (3 != argc) {
    printf("Usage : lzwunc squeezefilename newfilename\n");
    exit(0);
  }
  if ( -1 == (infd = open( *++argv, O_RDONLY )) ) {
    printf("Cant open %s\n", *argv);
    exit(0);
  }
  if ( -1 == (outfd = creat(*++argv,0666)) ) {
    printf("Cant create %s\n",*argv);
    exit(0);
  }

  is_a_con = isatty(outfd);		/* suppress dots if it is	 */
  init_tab();				/* set up atomic code definitions*/
  code = oldcode = getcode(infd);
  c = string_tab[code].follower;		/* first code always known	*/
  writec(outfd,c);
  finchar = c;

  while ( EOF != (code = incode = getcode(infd)) ) {
    ep = &string_tab[code];		/* initialize pointer		*/
    if ( !ep->used ) {			/* if code isn't known		*/
      writec(outfd,finchar);		/* the follower char of last	*/
      code = oldcode;			/* revert to last known code	*/
      incode = hash(oldcode,finchar,NO_UPDATE);
      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];
    }

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

    finchar = ep->follower;
    writec(outfd, finchar);
#ifdef DEBUG
    putchar(finchar);
#endif
    /* pop anything stacked during code parsing				*/
    while ( EMPTY != (tempc = pop()) ) {
      writec(outfd,tempc);
#ifdef DEBUG
    putchar(tempc);
#endif
    }
    if ( code_count ) {
      upd_tab(oldcode,finchar);
      --code_count;
    }
    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)
int c;
{
  stack[sp] = ((char) c);/* coerce passed integer into a character	*/
  ++sp;
  if (sp >= STACKSIZE) {
    printf("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;
}