plan9port

compress.c (32464B)

---

 /*
  * compress - File compression ala IEEE Computer, June 1984.
  *
  * Algorithm from "A Technique for High Performance Data Compression",
  * Terry A. Welch, IEEE Computer Vol 17, No 6 (June 1984), pp 8-19.
  *
  * Usage: compress [-dfvc] [-b bits] [file ...]
  * Inputs:
  *	-b:	limit the max number of bits/code.
  *	-c:	write output on stdout, don't remove original.
  *	-d:	decompress instead.
  *	-f:	Forces output file to be generated, even if one already
  *		exists, and even if no space is saved by compressing.
  *		If -f is not used, the user will be prompted if stdin is
  *		a tty, otherwise, the output file will not be overwritten.
  *	-v:	Write compression statistics
  *
  * 	file ...: Files to be compressed.  If none specified, stdin is used.
  * Outputs:
  *	file.Z:	Compressed form of file with same mode, owner, and utimes
  * 		or stdout (if stdin used as input)
  *
  * Assumptions:
  *	When filenames are given, replaces with the compressed version
  *	(.Z suffix) only if the file decreases in size.
  * Algorithm:
  * 	Modified Lempel-Ziv method (LZW).  Basically finds common
  * substrings and replaces them with a variable size code.  This is
  * deterministic, and can be done on the fly.  Thus, the decompression
  * procedure needs no input table, but tracks the way the table was built.
 
  * Authors:	Spencer W. Thomas	(decvax!harpo!utah-cs!utah-gr!thomas)
  *		Jim McKie		(decvax!mcvax!jim)
  *		Steve Davies		(decvax!vax135!petsd!peora!srd)
  *		Ken Turkowski		(decvax!decwrl!turtlevax!ken)
  *		James A. Woods		(decvax!ihnp4!ames!jaw)
  *		Joe Orost		(decvax!vax135!petsd!joe)
  */
 
 #ifndef USED
 #  define USED(x) if(x);else
 #endif
 
 #define _PLAN9_SOURCE
 #define _BSD_EXTENSION
 #define _POSIX_SOURCE
 
 #include <u.h>
 #include <stdio.h>
 #include <ctype.h>
 #include <stdlib.h>
 #include <unistd.h>
 #include <string.h>
 #include <signal.h>
 #include <utime.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 
 #define	min(a,b)	((a>b) ? b : a)
 
 #define BITS	16
 #define HSIZE	69001		/* 95% occupancy */
 
 /*
  * a code_int must be able to hold 2**BITS values of type int, and also -1
  */
 typedef long	code_int;
 typedef long	count_int;
 
 static char rcs_ident[] = "$Header: compress.c,v 4.0 85/07/30 12:50:00 joe Release $";
 
 uchar magic_header[] = { 0x1F, 0x9D };	/* 1F 9D */
 
 /* Defines for third byte of header */
 #define BIT_MASK	0x1f
 #define BLOCK_MASK	0x80
 /* Masks 0x40 and 0x20 are free.  I think 0x20 should mean that there is
 	a fourth header byte (for expansion).
 */
 #define INIT_BITS 9			/* initial number of bits/code */
 
 #define ARGVAL() (*++(*argv) || (--argc && *++argv))
 
 int n_bits;				/* number of bits/code */
 int maxbits = BITS;			/* user settable max # bits/code */
 code_int maxcode;			/* maximum code, given n_bits */
 code_int maxmaxcode = 1 << BITS;	/* should NEVER generate this code */
 
 #define MAXCODE(n_bits)	((1 << (n_bits)) - 1)
 
 count_int htab[HSIZE];
 ushort codetab[HSIZE];
 
 #define htabof(i)	htab[i]
 #define codetabof(i)	codetab[i]
 
 code_int hsize = HSIZE;			/* for dynamic table sizing */
 count_int fsize;
 
 /*
  * To save much memory, we overlay the table used by compress() with those
  * used by decompress().  The tab_prefix table is the same size and type
  * as the codetab.  The tab_suffix table needs 2**BITS characters.  We
  * get this from the beginning of htab.  The output stack uses the rest
  * of htab, and contains characters.  There is plenty of room for any
  * possible stack (stack used to be 8000 characters).
  */
 
 #define tab_prefixof(i)	codetabof(i)
 #define tab_suffixof(i)	((uchar *)(htab))[i]
 #define de_stack		((uchar *)&tab_suffixof(1<<BITS))
 
 code_int free_ent = 0;			/* first unused entry */
 int exit_stat = 0;
 
 void	cl_block(void);
 void	cl_hash(count_int);
 void	compress(void);
 void	copystat(char *, char *);
 void	decompress(void);
 int	foreground(void);
 code_int getcode(void);
 void	onintr(int);
 void	oops(int);
 void	output(code_int);
 void	prratio(FILE *, long, long);
 void	version(void);
 void	writeerr(void);
 
 void
 Usage(void)
 {
 #ifdef DEBUG
 	fprintf(stderr,"Usage: compress [-cdfDV] [-b maxbits] [file ...]\n");
 #else
 	fprintf(stderr,"Usage: compress [-cdfvV] [-b maxbits] [file ...]\n");
 #endif /* DEBUG */
 }
 
 int debug = 0;
 int nomagic = 0;	/* Use a 3-byte magic number header, unless old file */
 int zcat_flg = 0;	/* Write output on stdout, suppress messages */
 int quiet = 1;		/* don't tell me about compression */
 
 /*
  * block compression parameters -- after all codes are used up,
  * and compression rate changes, start over.
  */
 int block_compress = BLOCK_MASK;
 int clear_flg = 0;
 long ratio = 0;
 #define CHECK_GAP 10000	/* ratio check interval */
 count_int checkpoint = CHECK_GAP;
 /*
  * the next two codes should not be changed lightly, as they must not
  * lie within the contiguous general code space.
  */
 #define FIRST	257	/* first free entry */
 #define	CLEAR	256	/* table clear output code */
 
 int force = 0;
 char ofname [100];
 #ifdef DEBUG
 int verbose = 0;
 #endif /* DEBUG */
 void (*bgnd_flag)(int);
 
 int do_decomp = 0;
 
 int
 main(argc, argv)
 int argc;
 char **argv;
 {
 	int overwrite = 0;	/* Do not overwrite unless given -f flag */
 	char tempname[512];
 	char **filelist, **fileptr;
 	char *cp;
 	struct stat statbuf;
 
 	if ( (bgnd_flag = signal ( SIGINT, SIG_IGN )) != SIG_IGN ) {
 		signal(SIGINT, onintr);
 		signal(SIGSEGV, oops);
 	}
 
 	filelist = fileptr = (char **)(malloc(argc * sizeof(*argv)));
 	*filelist = NULL;
 
 	if((cp = strrchr(argv[0], '/')) != 0)
 		cp++;
 	else
 		cp = argv[0];
 	if(strcmp(cp, "uncompress") == 0)
 		do_decomp = 1;
 	else if(strcmp(cp, "zcat") == 0) {
 		do_decomp = 1;
 		zcat_flg = 1;
 	}
 
 	/*
 	 * Argument Processing
 	 * All flags are optional.
 	 * -C	generate output compatible with compress 2.0.
 	 * -D	debug
 	 * -V	print Version; debug verbose
 	 * -b maxbits	maxbits.  If -b is specified, then maxbits MUST be
 	 *		given also.
 	 * -c	cat all output to stdout
 	 * -d	do_decomp
 	 * -f	force overwrite of output file
 	 * -n	no header: useful to uncompress old files
 	 * -v	unquiet
 	 * if a string is left, must be an input filename.
 	 */
 	for (argc--, argv++; argc > 0; argc--, argv++) {
 	if (**argv == '-') {	/* A flag argument */
 		while (*++(*argv)) {	/* Process all flags in this arg */
 		switch (**argv) {
 		case 'C':
 			block_compress = 0;
 			break;
 #ifdef DEBUG
 		case 'D':
 			debug = 1;
 			break;
 		case 'V':
 			verbose = 1;
 			version();
 			break;
 #else
 		case 'V':
 			version();
 			break;
 #endif
 		case 'b':
 			if (!ARGVAL()) {
 				fprintf(stderr, "Missing maxbits\n");
 				Usage();
 				exit(1);
 			}
 			maxbits = atoi(*argv);
 			goto nextarg;
 		case 'c':
 			zcat_flg = 1;
 			break;
 		case 'd':
 			do_decomp = 1;
 			break;
 		case 'f':
 		case 'F':
 			overwrite = 1;
 			force = 1;
 			break;
 		case 'n':
 			nomagic = 1;
 			break;
 		case 'q':
 			quiet = 1;
 			break;
 		case 'v':
 			quiet = 0;
 			break;
 		default:
 			fprintf(stderr, "Unknown flag: '%c'; ", **argv);
 			Usage();
 			exit(1);
 		}
 		}
 	} else {			/* Input file name */
 		*fileptr++ = *argv;	/* Build input file list */
 		*fileptr = NULL;
 		/* process nextarg; */
 	}
 nextarg:
 		continue;
 	}
 
 	if(maxbits < INIT_BITS) maxbits = INIT_BITS;
 	if (maxbits > BITS) maxbits = BITS;
 	maxmaxcode = 1 << maxbits;
 
 	if (*filelist != NULL) {
 	for (fileptr = filelist; *fileptr; fileptr++) {
 		exit_stat = 0;
 		if (do_decomp != 0) {			/* DECOMPRESSION */
 		/* Check for .Z suffix */
 		if (strcmp(*fileptr + strlen(*fileptr) - 2, ".Z") != 0) {
 			/* No .Z: tack one on */
 			strcpy(tempname, *fileptr);
 			strcat(tempname, ".Z");
 			*fileptr = tempname;
 		}
 		/* Open input file */
 		if ((freopen(*fileptr, "r", stdin)) == NULL) {
 			perror(*fileptr);
 			continue;
 		}
 		/* Check the magic number */
 		if (nomagic == 0) {
 			if ((getchar() != (magic_header[0] & 0xFF))
 			|| (getchar() != (magic_header[1] & 0xFF))) {
 				fprintf(stderr, "%s: not in compressed format\n",
 					*fileptr);
 				continue;
 			}
 			maxbits = getchar();	/* set -b from file */
 			block_compress = maxbits & BLOCK_MASK;
 			maxbits &= BIT_MASK;
 			maxmaxcode = 1 << maxbits;
 			if(maxbits > BITS) {
 				fprintf(stderr,
 		"%s: compressed with %d bits, can only handle %d bits\n",
 					*fileptr, maxbits, BITS);
 				continue;
 			}
 		}
 		/* Generate output filename */
 		strcpy(ofname, *fileptr);
 		ofname[strlen(*fileptr) - 2] = '\0';  /* Strip off .Z */
 		} else {				/* COMPRESSION */
 		if (strcmp(*fileptr + strlen(*fileptr) - 2, ".Z") == 0) {
 			fprintf(stderr,
 				"%s: already has .Z suffix -- no change\n",
 				*fileptr);
 			continue;
 		}
 		/* Open input file */
 		if ((freopen(*fileptr, "r", stdin)) == NULL) {
 			perror(*fileptr);
 			continue;
 		}
 		(void) stat(*fileptr, &statbuf);
 		fsize = (long) statbuf.st_size;
 		/*
 		 * tune hash table size for small files -- ad hoc,
 		 * but the sizes match earlier #defines, which
 		 * serve as upper bounds on the number of output codes.
 		 */
 		hsize = HSIZE;
 		if (fsize < (1 << 12))
 			hsize = min(5003, HSIZE);
 		else if (fsize < (1 << 13))
 			hsize = min(9001, HSIZE);
 		else if (fsize < (1 << 14))
 			hsize = min (18013, HSIZE);
 		else if (fsize < (1 << 15))
 			hsize = min (35023, HSIZE);
 		else if (fsize < 47000)
 			hsize = min (50021, HSIZE);
 
 		/* Generate output filename */
 		strcpy(ofname, *fileptr);
 #ifndef BSD4_2
 		if ((cp=strrchr(ofname,'/')) != NULL)
 			cp++;
 		else
 			cp = ofname;
 		/*
 		 *** changed 12 to 25;  should be NAMELEN-3, but I don't want
 		 * to fight the headers.	ehg 5 Nov 92 **
 		 */
 		if (strlen(cp) > 25) {
 			fprintf(stderr, "%s: filename too long to tack on .Z\n",
 				cp);
 			continue;
 		}
 #endif
 		strcat(ofname, ".Z");
 		}
 		/* Check for overwrite of existing file */
 		if (overwrite == 0 && zcat_flg == 0 &&
 		   stat(ofname, &statbuf) == 0) {
 			char response[2];
 
 			response[0] = 'n';
 			fprintf(stderr, "%s already exists;", ofname);
 			if (foreground()) {
 				fprintf(stderr,
 				    " do you wish to overwrite %s (y or n)? ",
 					ofname);
 				fflush(stderr);
 				(void) read(2, response, 2);
 				while (response[1] != '\n')
 					if (read(2, response+1, 1) < 0) {
 						/* Ack! */
 						perror("stderr");
 						break;
 					}
 			}
 			if (response[0] != 'y') {
 				fprintf(stderr, "\tnot overwritten\n");
 				continue;
 			}
 		}
 		if(zcat_flg == 0) {		/* Open output file */
 			if (freopen(ofname, "w", stdout) == NULL) {
 				perror(ofname);
 				continue;
 			}
 			if(!quiet)
 				fprintf(stderr, "%s: ", *fileptr);
 		}
 
 		/* Actually do the compression/decompression */
 		if (do_decomp == 0)
 			compress();
 #ifndef DEBUG
 		else
 			decompress();
 #else
 		else if (debug == 0)
 			decompress();
 		else
 			printcodes();
 		if (verbose)
 			dump_tab();
 #endif						/* DEBUG */
 		if(zcat_flg == 0) {
 			copystat(*fileptr, ofname);	/* Copy stats */
 			if (exit_stat == 1 || !quiet)
 				putc('\n', stderr);
 		}
 	}
 	} else {		/* Standard input */
 	if (do_decomp == 0) {
 		compress();
 #ifdef DEBUG
 		if(verbose)
 			dump_tab();
 #endif
 		if(!quiet)
 			putc('\n', stderr);
 	} else {
 		/* Check the magic number */
 		if (nomagic == 0) {
 		if ((getchar()!=(magic_header[0] & 0xFF))
 		 || (getchar()!=(magic_header[1] & 0xFF))) {
 			fprintf(stderr, "stdin: not in compressed format\n");
 			exit(1);
 		}
 		maxbits = getchar();	/* set -b from file */
 		block_compress = maxbits & BLOCK_MASK;
 		maxbits &= BIT_MASK;
 		maxmaxcode = 1 << maxbits;
 		fsize = 100000;		/* assume stdin large for USERMEM */
 		if(maxbits > BITS) {
 			fprintf(stderr,
 			"stdin: compressed with %d bits, can only handle %d bits\n",
 			maxbits, BITS);
 			exit(1);
 		}
 		}
 #ifndef DEBUG
 		decompress();
 #else
 		if (debug == 0)
 			decompress();
 		else
 			printcodes();
 		if (verbose)
 			dump_tab();
 #endif						/* DEBUG */
 	}
 	}
 	exit(exit_stat);
 	return 0;
 }
 
 static int offset;
 long in_count = 1;		/* length of input */
 long bytes_out;			/* length of compressed output */
 long out_count = 0;		/* # of codes output (for debugging) */
 
 /*
  * compress stdin to stdout
  *
  * Algorithm:  use open addressing double hashing (no chaining) on the
  * prefix code / next character combination.  We do a variant of Knuth's
  * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
  * secondary probe.  Here, the modular division first probe is gives way
  * to a faster exclusive-or manipulation.  Also do block compression with
  * an adaptive reset, whereby the code table is cleared when the compression
  * ratio decreases, but after the table fills.  The variable-length output
  * codes are re-sized at this point, and a special CLEAR code is generated
  * for the decompressor.  Late addition:  construct the table according to
  * file size for noticeable speed improvement on small files.  Please direct
  * questions about this implementation to ames!jaw.
  */
 void
 compress(void)
 {
 	code_int ent, hsize_reg;
 	code_int i;
 	int c, disp, hshift;
 	long fcode;
 
 	if (nomagic == 0) {
 		putchar(magic_header[0]);
 		putchar(magic_header[1]);
 		putchar((char)(maxbits | block_compress));
 		if(ferror(stdout))
 			writeerr();
 	}
 	offset = 0;
 	bytes_out = 3;		/* includes 3-byte header mojo */
 	out_count = 0;
 	clear_flg = 0;
 	ratio = 0;
 	in_count = 1;
 	checkpoint = CHECK_GAP;
 	maxcode = MAXCODE(n_bits = INIT_BITS);
 	free_ent = (block_compress? FIRST: 256);
 
 	ent = getchar ();
 
 	hshift = 0;
 	for (fcode = (long)hsize;  fcode < 65536L; fcode *= 2)
 		hshift++;
 	hshift = 8 - hshift;		/* set hash code range bound */
 
 	hsize_reg = hsize;
 	cl_hash( (count_int) hsize_reg);		/* clear hash table */
 
 	while ((c = getchar()) != EOF) {
 		in_count++;
 		fcode = (long) (((long) c << maxbits) + ent);
 	 	i = ((c << hshift) ^ ent);	/* xor hashing */
 
 		if (htabof (i) == fcode) {
 			ent = codetabof(i);
 			continue;
 		} else if ((long)htabof(i) < 0 )	/* empty slot */
 			goto nomatch;
 	 	disp = hsize_reg - i;	/* secondary hash (after G. Knott) */
 		if (i == 0)
 			disp = 1;
 probe:
 		if ((i -= disp) < 0)
 			i += hsize_reg;
 
 		if (htabof (i) == fcode) {
 			ent = codetabof(i);
 			continue;
 		}
 		if ((long)htabof(i) > 0)
 			goto probe;
 nomatch:
 		output((code_int)ent);
 		out_count++;
 	 	ent = c;
 		if (free_ent < maxmaxcode) {
 	 		codetabof(i) = free_ent++;	/* code -> hashtable */
 			htabof(i) = fcode;
 		} else if ((count_int)in_count >= checkpoint && block_compress)
 			cl_block ();
 	}
 	/*
 	* Put out the final code.
 	*/
 	output( (code_int)ent );
 	out_count++;
 	output( (code_int)-1 );
 
 	/*
 	* Print out stats on stderr
 	*/
 	if(zcat_flg == 0 && !quiet) {
 #ifdef DEBUG
 	fprintf( stderr,
 		"%ld chars in, %ld codes (%ld bytes) out, compression factor: ",
 		in_count, out_count, bytes_out );
 	prratio( stderr, in_count, bytes_out );
 	fprintf( stderr, "\n");
 	fprintf( stderr, "\tCompression as in compact: " );
 	prratio( stderr, in_count-bytes_out, in_count );
 	fprintf( stderr, "\n");
 	fprintf( stderr, "\tLargest code (of last block) was %d (%d bits)\n",
 		free_ent - 1, n_bits );
 #else /* !DEBUG */
 	fprintf( stderr, "Compression: " );
 	prratio( stderr, in_count-bytes_out, in_count );
 #endif /* DEBUG */
 	}
 	if(bytes_out > in_count)	/* exit(2) if no savings */
 		exit_stat = 2;
 }
 
 /*
  * TAG( output )
  *
  * Output the given code.
  * Inputs:
  * 	code:	A n_bits-bit integer.  If == -1, then EOF.  This assumes
  *		that n_bits =< (long)wordsize - 1.
  * Outputs:
  * 	Outputs code to the file.
  * Assumptions:
  *	Chars are 8 bits long.
  * Algorithm:
  * 	Maintain a BITS character long buffer (so that 8 codes will
  * fit in it exactly).  When the buffer fills up empty it and start over.
  */
 
 static char buf[BITS];
 
 uchar lmask[9] = {0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80, 0x00};
 uchar rmask[9] = {0x00, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff};
 
 void
 output( code )
 code_int  code;
 {
 #ifdef DEBUG
 	static int col = 0;
 #endif
 	int r_off = offset, bits= n_bits;
 	char *bp = buf;
 
 #ifdef DEBUG
 	if (verbose)
 		fprintf(stderr, "%5d%c", code,
 			(col+=6) >= 74? (col = 0, '\n'): ' ');
 #endif
 	if (code >= 0) {
 		/*
 		 * byte/bit numbering on the VAX is simulated by the
 		 * following code
 		 */
 		/*
 		 * Get to the first byte.
 		 */
 		bp += (r_off >> 3);
 		r_off &= 7;
 		/*
 		 * Since code is always >= 8 bits, only need to mask the first
 		 * hunk on the left.
 		 */
 		*bp = (*bp & rmask[r_off]) | (code << r_off) & lmask[r_off];
 		bp++;
 		bits -=  8 - r_off;
 		code >>= 8 - r_off;
 		/* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
 		if ( bits >= 8 ) {
 			*bp++ = code;
 			code >>= 8;
 			bits -= 8;
 		}
 		/* Last bits. */
 		if(bits)
 			*bp = code;
 
 		offset += n_bits;
 		if ( offset == (n_bits << 3) ) {
 			bp = buf;
 			bits = n_bits;
 			bytes_out += bits;
 			do {
 				putchar(*bp++);
 			} while(--bits);
 			offset = 0;
 		}
 
 		/*
 		 * If the next entry is going to be too big for the code size,
 		 * then increase it, if possible.
 		 */
 		if ( free_ent > maxcode || (clear_flg > 0)) {
 			/*
 			* Write the whole buffer, because the input side won't
 			* discover the size increase until after it has read it.
 			*/
 			if ( offset > 0 ) {
 				if( fwrite( buf, 1, n_bits, stdout ) != n_bits)
 					writeerr();
 				bytes_out += n_bits;
 			}
 			offset = 0;
 
 			if ( clear_flg ) {
 				maxcode = MAXCODE (n_bits = INIT_BITS);
 				clear_flg = 0;
 			} else {
 				n_bits++;
 				if ( n_bits == maxbits )
 					maxcode = maxmaxcode;
 				else
 					maxcode = MAXCODE(n_bits);
 			}
 #ifdef DEBUG
 			if ( debug ) {
 				fprintf(stderr,
 					"\nChange to %d bits\n", n_bits);
 				col = 0;
 			}
 #endif
 		}
 	} else {
 		/*
 		 * At EOF, write the rest of the buffer.
 		 */
 		if ( offset > 0 )
 			fwrite( buf, 1, (offset + 7) / 8, stdout );
 		bytes_out += (offset + 7) / 8;
 		offset = 0;
 		fflush( stdout );
 #ifdef DEBUG
 		if ( verbose )
 			fprintf( stderr, "\n" );
 #endif
 		if( ferror( stdout ) )
 			writeerr();
 	}
 }
 
 /*
  * Decompress stdin to stdout.  This routine adapts to the codes in the
  * file building the "string" table on-the-fly; requiring no table to
  * be stored in the compressed file.  The tables used herein are shared
  * with those of the compress() routine.  See the definitions above.
  */
 void
 decompress(void)
 {
 	int finchar;
 	code_int code, oldcode, incode;
 	uchar *stackp;
 
 	/*
 	* As above, initialize the first 256 entries in the table.
 	*/
 	maxcode = MAXCODE(n_bits = INIT_BITS);
 	for (code = 255; code >= 0; code--) {
 		tab_prefixof(code) = 0;
 		tab_suffixof(code) = (uchar)code;
 	}
 	free_ent = (block_compress? FIRST: 256);
 
 	finchar = oldcode = getcode();
 	if(oldcode == -1)		/* EOF already? */
 		return;			/* Get out of here */
 	putchar((char)finchar);		/* first code must be 8 bits = char */
 	if(ferror(stdout))		/* Crash if can't write */
 		writeerr();
 	stackp = de_stack;
 
 	while ((code = getcode()) > -1) {
 		if ((code == CLEAR) && block_compress) {
 			for (code = 255; code >= 0; code--)
 				tab_prefixof(code) = 0;
 			clear_flg = 1;
 			free_ent = FIRST - 1;
 			if ((code = getcode()) == -1)	/* O, untimely death! */
 				break;
 		}
 		incode = code;
 		/*
 		 * Special case for KwKwK string.
 		 */
 		if (code >= free_ent) {
 			*stackp++ = finchar;
 			code = oldcode;
 		}
 
 		/*
 		 * Generate output characters in reverse order
 		 */
 		while (code >= 256) {
 			*stackp++ = tab_suffixof(code);
 			code = tab_prefixof(code);
 		}
 		*stackp++ = finchar = tab_suffixof(code);
 
 		/*
 		 * And put them out in forward order
 		 */
 		do {
 			putchar(*--stackp);
 		} while (stackp > de_stack);
 
 		/*
 		 * Generate the new entry.
 		 */
 		if ( (code=free_ent) < maxmaxcode ) {
 			tab_prefixof(code) = (ushort)oldcode;
 			tab_suffixof(code) = finchar;
 			free_ent = code+1;
 		}
 		/*
 		 * Remember previous code.
 		 */
 		oldcode = incode;
 	}
 	fflush(stdout);
 	if(ferror(stdout))
 		writeerr();
 }
 
 /*
  * TAG( getcode )
  *
  * Read one code from the standard input.  If EOF, return -1.
  * Inputs:
  * 	stdin
  * Outputs:
  * 	code or -1 is returned.
  */
 code_int
 getcode()
 {
 	int r_off, bits;
 	code_int code;
 	static int offset = 0, size = 0;
 	static uchar buf[BITS];
 	uchar *bp = buf;
 
 	if ( clear_flg > 0 || offset >= size || free_ent > maxcode ) {
 		/*
 		 * If the next entry will be too big for the current code
 		 * size, then we must increase the size.  This implies reading
 		 * a new buffer full, too.
 		 */
 		if ( free_ent > maxcode ) {
 			n_bits++;
 			if ( n_bits == maxbits )
 				maxcode = maxmaxcode; /* won't get any bigger now */
 			else
 				maxcode = MAXCODE(n_bits);
 		}
 		if ( clear_flg > 0) {
 			maxcode = MAXCODE(n_bits = INIT_BITS);
 			clear_flg = 0;
 		}
 		size = fread(buf, 1, n_bits, stdin);
 		if (size <= 0)
 			return -1;			/* end of file */
 		offset = 0;
 		/* Round size down to integral number of codes */
 		size = (size << 3) - (n_bits - 1);
 	}
 	r_off = offset;
 	bits = n_bits;
 	/*
 	 * Get to the first byte.
 	 */
 	bp += (r_off >> 3);
 	r_off &= 7;
 	/* Get first part (low order bits) */
 	code = (*bp++ >> r_off);
 	bits -= (8 - r_off);
 	r_off = 8 - r_off;		/* now, offset into code word */
 	/* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
 	if (bits >= 8) {
 		code |= *bp++ << r_off;
 		r_off += 8;
 		bits -= 8;
 	}
 	/* high order bits. */
 	code |= (*bp & rmask[bits]) << r_off;
 	offset += n_bits;
 	return code;
 }
 
 #ifdef DEBUG
 printcodes()
 {
 	/*
 	* Just print out codes from input file.  For debugging.
 	*/
 	code_int code;
 	int col = 0, bits;
 
 	bits = n_bits = INIT_BITS;
 	maxcode = MAXCODE(n_bits);
 	free_ent = ((block_compress) ? FIRST : 256 );
 	while ( ( code = getcode() ) >= 0 ) {
 	if ( (code == CLEAR) && block_compress ) {
 			free_ent = FIRST - 1;
 			clear_flg = 1;
 	}
 	else if ( free_ent < maxmaxcode )
 		free_ent++;
 	if ( bits != n_bits ) {
 		fprintf(stderr, "\nChange to %d bits\n", n_bits );
 		bits = n_bits;
 		col = 0;
 	}
 	fprintf(stderr, "%5d%c", code, (col+=6) >= 74 ? (col = 0, '\n') : ' ' );
 	}
 	putc( '\n', stderr );
 	exit( 0 );
 }
 
 code_int sorttab[1<<BITS];	/* sorted pointers into htab */
 
 #define STACK_SIZE	15000
 
 dump_tab()	/* dump string table */
 {
 	int i, first, c, ent;
 	int stack_top = STACK_SIZE;
 
 	if(do_decomp == 0) {	/* compressing */
 	int flag = 1;
 
 	for(i=0; i<hsize; i++) {	/* build sort pointers */
 		if((long)htabof(i) >= 0) {
 			sorttab[codetabof(i)] = i;
 		}
 	}
 	first = block_compress ? FIRST : 256;
 	for(i = first; i < free_ent; i++) {
 		fprintf(stderr, "%5d: \"", i);
 		de_stack[--stack_top] = '\n';
 		de_stack[--stack_top] = '"';
 		stack_top = in_stack((htabof(sorttab[i])>>maxbits)&0xff,
 	stack_top);
 		for(ent=htabof(sorttab[i]) & ((1<<maxbits)-1);
 			ent > 256;
 			ent=htabof(sorttab[ent]) & ((1<<maxbits)-1)) {
 			stack_top = in_stack(htabof(sorttab[ent]) >> maxbits,
 						stack_top);
 		}
 		stack_top = in_stack(ent, stack_top);
 		fwrite( &de_stack[stack_top], 1, STACK_SIZE-stack_top, stderr);
 			stack_top = STACK_SIZE;
 	}
 	} else if(!debug) {	/* decompressing */
 
 	for ( i = 0; i < free_ent; i++ ) {
 		ent = i;
 		c = tab_suffixof(ent);
 		if ( isascii(c) && isprint(c) )
 		fprintf( stderr, "%5d: %5d/'%c'  \"",
 				ent, tab_prefixof(ent), c );
 		else
 		fprintf( stderr, "%5d: %5d/\\%03o \"",
 				ent, tab_prefixof(ent), c );
 		de_stack[--stack_top] = '\n';
 		de_stack[--stack_top] = '"';
 		for ( ; ent != NULL;
 			ent = (ent >= FIRST ? tab_prefixof(ent) : NULL) ) {
 		stack_top = in_stack(tab_suffixof(ent), stack_top);
 		}
 		fwrite( &de_stack[stack_top], 1, STACK_SIZE - stack_top, stderr );
 		stack_top = STACK_SIZE;
 	}
 	}
 }
 
 int
 in_stack(int c, int stack_top)
 {
 	if ( (isascii(c) && isprint(c) && c != '\\') || c == ' ' ) {
 		de_stack[--stack_top] = c;
 	} else {
 		switch( c ) {
 		case '\n': de_stack[--stack_top] = 'n'; break;
 		case '\t': de_stack[--stack_top] = 't'; break;
 		case '\b': de_stack[--stack_top] = 'b'; break;
 		case '\f': de_stack[--stack_top] = 'f'; break;
 		case '\r': de_stack[--stack_top] = 'r'; break;
 		case '\\': de_stack[--stack_top] = '\\'; break;
 		default:
 	 	de_stack[--stack_top] = '0' + c % 8;
 	 	de_stack[--stack_top] = '0' + (c / 8) % 8;
 	 	de_stack[--stack_top] = '0' + c / 64;
 	 	break;
 		}
 		de_stack[--stack_top] = '\\';
 	}
 	return stack_top;
 }
 #endif /* DEBUG */
 
 void
 writeerr(void)
 {
 	perror(ofname);
 	unlink(ofname);
 	exit(1);
 }
 
 void
 copystat(ifname, ofname)
 char *ifname, *ofname;
 {
 	int mode;
 	time_t timep[2];			/* should be struct utimbuf */
 	struct stat statbuf;
 
 	fclose(stdout);
 	if (stat(ifname, &statbuf)) {		/* Get stat on input file */
 		perror(ifname);
 		return;
 	}
 	if (!S_ISREG(statbuf.st_mode)) {
 		if (quiet)
 			fprintf(stderr, "%s: ", ifname);
 		fprintf(stderr, " -- not a regular file: unchanged");
 		exit_stat = 1;
 	} else if (exit_stat == 2 && !force) {
 		/* No compression: remove file.Z */
 		if (!quiet)
 			fprintf(stderr, " -- file unchanged");
 	} else {			/* Successful Compression */
 		exit_stat = 0;
 		mode = statbuf.st_mode & 0777;
 		if (chmod(ofname, mode))		/* Copy modes */
 			perror(ofname);
 		/* Copy ownership */
 		chown(ofname, statbuf.st_uid, statbuf.st_gid);
 		timep[0] = statbuf.st_atime;
 		timep[1] = statbuf.st_mtime;
 		/* Update last accessed and modified times */
 		utime(ofname, (struct utimbuf *)timep);
 //		if (unlink(ifname))	/* Remove input file */
 //			perror(ifname);
 		return;			/* success */
 	}
 
 	/* Unsuccessful return -- one of the tests failed */
 	if (unlink(ofname))
 		perror(ofname);
 }
 
 /*
  * This routine returns 1 if we are running in the foreground and stderr
  * is a tty.
  */
 int
 foreground(void)
 {
 	if(bgnd_flag)			/* background? */
 		return 0;
 	else				/* foreground */
 		return isatty(2);	/* and stderr is a tty */
 }
 
 void
 onintr(int x)
 {
 	USED(x);
 	unlink(ofname);
 	exit(1);
 }
 
 void
 oops(int x)		/* wild pointer -- assume bad input */
 {
 	USED(x);
 	if (do_decomp == 1)
 		fprintf(stderr, "uncompress: corrupt input\n");
 	unlink(ofname);
 	exit(1);
 }
 
 void
 cl_block(void)		/* table clear for block compress */
 {
 	long rat;
 
 	checkpoint = in_count + CHECK_GAP;
 #ifdef DEBUG
 	if ( debug ) {
 		fprintf ( stderr, "count: %ld, ratio: ", in_count );
 		prratio ( stderr, in_count, bytes_out );
 		fprintf ( stderr, "\n");
 	}
 #endif /* DEBUG */
 
 	if (in_count > 0x007fffff) {	/* shift will overflow */
 		rat = bytes_out >> 8;
 		if (rat == 0)		/* Don't divide by zero */
 			rat = 0x7fffffff;
 		else
 			rat = in_count / rat;
 	} else
 		rat = (in_count << 8) / bytes_out;	/* 8 fractional bits */
 	if (rat > ratio)
 		ratio = rat;
 	else {
 		ratio = 0;
 #ifdef DEBUG
 		if (verbose)
 			dump_tab();	/* dump string table */
 #endif
 		cl_hash((count_int)hsize);
 		free_ent = FIRST;
 		clear_flg = 1;
 		output((code_int)CLEAR);
 #ifdef DEBUG
 		if (debug)
 			fprintf(stderr, "clear\n");
 #endif /* DEBUG */
 	}
 }
 
 void
 cl_hash(count_int hsize)		/* reset code table */
 {
 	count_int *htab_p = htab+hsize;
 	long i;
 	long m1 = -1;
 
 	i = hsize - 16;
  	do {				/* might use Sys V memset(3) here */
 		*(htab_p-16) = m1;
 		*(htab_p-15) = m1;
 		*(htab_p-14) = m1;
 		*(htab_p-13) = m1;
 		*(htab_p-12) = m1;
 		*(htab_p-11) = m1;
 		*(htab_p-10) = m1;
 		*(htab_p-9) = m1;
 		*(htab_p-8) = m1;
 		*(htab_p-7) = m1;
 		*(htab_p-6) = m1;
 		*(htab_p-5) = m1;
 		*(htab_p-4) = m1;
 		*(htab_p-3) = m1;
 		*(htab_p-2) = m1;
 		*(htab_p-1) = m1;
 		htab_p -= 16;
 	} while ((i -= 16) >= 0);
 	for ( i += 16; i > 0; i-- )
 		*--htab_p = m1;
 }
 
 void
 prratio(stream, num, den)
 FILE *stream;
 long num, den;
 {
 	int q;				/* Doesn't need to be long */
 
 	if(num > 214748L)		/* 2147483647/10000 */
 		q = num / (den / 10000L);
 	else
 		q = 10000L * num / den;	/* Long calculations, though */
 	if (q < 0) {
 		putc('-', stream);
 		q = -q;
 	}
 	fprintf(stream, "%d.%02d%%", q / 100, q % 100);
 }
 
 void
 version(void)
 {
 	fprintf(stderr, "%s\n", rcs_ident);
 	fprintf(stderr, "Options: ");
 #ifdef DEBUG
 	fprintf(stderr, "DEBUG, ");
 #endif
 #ifdef BSD4_2
 	fprintf(stderr, "BSD4_2, ");
 #endif
 	fprintf(stderr, "BITS = %d\n", BITS);
 }
 
 /*
  * The revision-history novel:
  *
  * $Header: compress.c,v 4.0 85/07/30 12:50:00 joe Release $
  * $Log:	compress.c,v $
  * Revision 4.0  85/07/30  12:50:00  joe
  * Removed ferror() calls in output routine on every output except first.
  * Prepared for release to the world.
  *
  * Revision 3.6  85/07/04  01:22:21  joe
  * Remove much wasted storage by overlaying hash table with the tables
  * used by decompress: tab_suffix[1<<BITS], stack[8000].  Updated USERMEM
  * computations.  Fixed dump_tab() DEBUG routine.
  *
  * Revision 3.5  85/06/30  20:47:21  jaw
  * Change hash function to use exclusive-or.  Rip out hash cache.  These
  * speedups render the megamemory version defunct, for now.  Make decoder
  * stack global.  Parts of the RCS trunks 2.7, 2.6, and 2.1 no longer apply.
  *
  * Revision 3.4  85/06/27  12:00:00  ken
  * Get rid of all floating-point calculations by doing all compression ratio
  * calculations in fixed point.
  *
  * Revision 3.3  85/06/24  21:53:24  joe
  * Incorporate portability suggestion for M_XENIX.  Got rid of text on #else
  * and #endif lines.  Cleaned up #ifdefs for vax and interdata.
  *
  * Revision 3.2  85/06/06  21:53:24  jaw
  * Incorporate portability suggestions for Z8000, IBM PC/XT from mailing list.
  * Default to "quiet" output (no compression statistics).
  *
  * Revision 3.1  85/05/12  18:56:13  jaw
  * Integrate decompress() stack speedups (from early pointer mods by McKie).
  * Repair multi-file USERMEM gaffe.  Unify 'force' flags to mimic semantics
  * of SVR2 'pack'.  Streamline block-compress table clear logic.  Increase
  * output byte count by magic number size.
  *
  * Revision 3.0	84/11/27  11:50:00  petsd!joe
  * Set HSIZE depending on BITS.  Set BITS depending on USERMEM.  Unrolled
  * loops in clear routines.  Added "-C" flag for 2.0 compatibility.  Used
  * unsigned compares on Perkin-Elmer.  Fixed foreground check.
  *
  * Revision 2.7	84/11/16  19:35:39  ames!jaw
  * Cache common hash codes based on input statistics; this improves
  * performance for low-density raster images.  Pass on #ifdef bundle
  * from Turkowski.
  *
  * Revision 2.6	84/11/05  19:18:21  ames!jaw
  * Vary size of hash tables to reduce time for small files.
  * Tune PDP-11 hash function.
  *
  * Revision 2.5	84/10/30  20:15:14  ames!jaw
  * Junk chaining; replace with the simpler (and, on the VAX, faster)
  * double hashing, discussed within.  Make block compression standard.
  *
  * Revision 2.4	84/10/16  11:11:11  ames!jaw
  * Introduce adaptive reset for block compression, to boost the rate
  * another several percent.  (See mailing list notes.)
  *
  * Revision 2.3	84/09/22  22:00:00  petsd!joe
  * Implemented "-B" block compress.  Implemented REVERSE sorting of tab_next.
  * Bug fix for last bits.  Changed fwrite to putchar loop everywhere.
  *
  * Revision 2.2	84/09/18  14:12:21  ames!jaw
  * Fold in news changes, small machine typedef from thomas,
  * #ifdef interdata from joe.
  *
  * Revision 2.1	84/09/10  12:34:56  ames!jaw
  * Configured fast table lookup for 32-bit machines.
  * This cuts user time in half for b <= FBITS, and is useful for news batching
  * from VAX to PDP sites.  Also sped up decompress() [fwrite->putc] and
  * added signal catcher [plus beef in writeerr()] to delete effluvia.
  *
  * Revision 2.0	84/08/28  22:00:00  petsd!joe
  * Add check for foreground before prompting user.  Insert maxbits into
  * compressed file.  Force file being uncompressed to end with ".Z".
  * Added "-c" flag and "zcat".  Prepared for release.
  *
  * Revision 1.10  84/08/24  18:28:00  turtlevax!ken
  * Will only compress regular files (no directories), added a magic number
  * header (plus an undocumented -n flag to handle old files without headers),
  * added -f flag to force overwriting of possibly existing destination file,
  * otherwise the user is prompted for a response.  Will tack on a .Z to a
  * filename if it doesn't have one when decompressing.  Will only replace
  * file if it was compressed.
  *
  * Revision 1.9  84/08/16  17:28:00  turtlevax!ken
  * Removed scanargs(), getopt(), added .Z extension and unlimited number of
  * filenames to compress.  Flags may be clustered (-Ddvb12) or separated
  * (-D -d -v -b 12), or combination thereof.  Modes and other status is
  * copied with copystat().  -O bug for 4.2 seems to have disappeared with
  * 1.8.
  *
  * Revision 1.8  84/08/09  23:15:00  joe
  * Made it compatible with vax version, installed jim's fixes/enhancements
  *
  * Revision 1.6  84/08/01  22:08:00  joe
  * Sped up algorithm significantly by sorting the compress chain.
  *
  * Revision 1.5  84/07/13  13:11:00  srd
  * Added C version of vax asm routines.  Changed structure to arrays to
  * save much memory.  Do unsigned compares where possible (faster on
  * Perkin-Elmer)
  *
  * Revision 1.4  84/07/05  03:11:11  thomas
  * Clean up the code a little and lint it.  (Lint complains about all
  * the regs used in the asm, but I'm not going to "fix" this.)
  *
  * Revision 1.3  84/07/05  02:06:54  thomas
  * Minor fixes.
  *
  * Revision 1.2  84/07/05  00:27:27  thomas
  * Add variable bit length output.
  */