2 * Copyright (c) 1985, 1986, 1992, 1993
3 * The Regents of the University of California. All rights reserved.
5 * This code is derived from software contributed to Berkeley by
6 * Diomidis Spinellis and James A. Woods, derived from original
7 * work by Spencer Thomas and Joseph Orost.
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10 * modification, are permitted provided that the following conditions
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19 * This product includes software developed by the University of
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37 * @(#)zopen.c 8.1 (Berkeley) 6/27/93
38 * $FreeBSD: src/usr.bin/compress/zopen.c,v 1.5.6.1 2002/07/16 00:52:08 tjr Exp $
39 * $DragonFly: src/usr.bin/compress/zopen.c,v 1.2 2003/06/17 04:29:25 dillon Exp $
43 * fcompress.c - File compression ala IEEE Computer, June 1984.
46 * Spencer W. Thomas (decvax!utah-cs!thomas)
47 * Jim McKie (decvax!mcvax!jim)
48 * Steve Davies (decvax!vax135!petsd!peora!srd)
49 * Ken Turkowski (decvax!decwrl!turtlevax!ken)
50 * James A. Woods (decvax!ihnp4!ames!jaw)
51 * Joe Orost (decvax!vax135!petsd!joe)
53 * Cleaned up and converted to library returning I/O streams by
54 * Diomidis Spinellis <dds@doc.ic.ac.uk>.
56 * zopen(filename, mode, bits)
57 * Returns a FILE * that can be used for read or write. The modes
58 * supported are only "r" and "w". Seeking is not allowed. On
59 * reading the file is decompressed, on writing it is compressed.
60 * The output is compatible with compress(1) with 16 bit tables.
61 * Any file produced by compress(1) can be read.
64 #include <sys/param.h>
76 #define BITS 16 /* Default bits. */
77 #define HSIZE 69001 /* 95% occupancy */
79 /* A code_int must be able to hold 2**BITS values of type int, and also -1. */
80 typedef long code_int;
81 typedef long count_int;
83 typedef u_char char_type;
84 static char_type magic_header[] =
85 {'\037', '\235'}; /* 1F 9D */
87 #define BIT_MASK 0x1f /* Defines for third byte of header. */
88 #define BLOCK_MASK 0x80
91 * Masks 0x40 and 0x20 are free. I think 0x20 should mean that there is
92 * a fourth header byte (for expansion).
94 #define INIT_BITS 9 /* Initial number of bits/code. */
96 #define MAXCODE(n_bits) ((1 << (n_bits)) - 1)
99 FILE *zs_fp; /* File stream for I/O */
100 char zs_mode; /* r or w */
102 S_START, S_MIDDLE, S_EOF
103 } zs_state; /* State of computation */
104 u_int zs_n_bits; /* Number of bits/code. */
105 u_int zs_maxbits; /* User settable max # bits/code. */
106 code_int zs_maxcode; /* Maximum code, given n_bits. */
107 code_int zs_maxmaxcode; /* Should NEVER generate this code. */
108 count_int zs_htab [HSIZE];
109 u_short zs_codetab [HSIZE];
110 code_int zs_hsize; /* For dynamic table sizing. */
111 code_int zs_free_ent; /* First unused entry. */
113 * Block compression parameters -- after all codes are used up,
114 * and compression rate changes, start over.
116 int zs_block_compress;
119 count_int zs_checkpoint;
121 long zs_in_count; /* Length of input. */
122 long zs_bytes_out; /* Length of compressed output. */
123 long zs_out_count; /* # of codes output (for debugging). */
124 char_type zs_buf[BITS];
129 code_int zs_hsize_reg;
131 } w; /* Write paramenters */
133 char_type *zs_stackp;
135 code_int zs_code, zs_oldcode, zs_incode;
136 int zs_roffset, zs_size;
137 char_type zs_gbuf[BITS];
138 } r; /* Read parameters */
142 /* Definitions to retain old variable names */
144 #define zmode zs->zs_mode
145 #define state zs->zs_state
146 #define n_bits zs->zs_n_bits
147 #define maxbits zs->zs_maxbits
148 #define maxcode zs->zs_maxcode
149 #define maxmaxcode zs->zs_maxmaxcode
150 #define htab zs->zs_htab
151 #define codetab zs->zs_codetab
152 #define hsize zs->zs_hsize
153 #define free_ent zs->zs_free_ent
154 #define block_compress zs->zs_block_compress
155 #define clear_flg zs->zs_clear_flg
156 #define ratio zs->zs_ratio
157 #define checkpoint zs->zs_checkpoint
158 #define offset zs->zs_offset
159 #define in_count zs->zs_in_count
160 #define bytes_out zs->zs_bytes_out
161 #define out_count zs->zs_out_count
162 #define buf zs->zs_buf
163 #define fcode zs->u.w.zs_fcode
164 #define hsize_reg zs->u.w.zs_hsize_reg
165 #define ent zs->u.w.zs_ent
166 #define hshift zs->u.w.zs_hshift
167 #define stackp zs->u.r.zs_stackp
168 #define finchar zs->u.r.zs_finchar
169 #define code zs->u.r.zs_code
170 #define oldcode zs->u.r.zs_oldcode
171 #define incode zs->u.r.zs_incode
172 #define roffset zs->u.r.zs_roffset
173 #define size zs->u.r.zs_size
174 #define gbuf zs->u.r.zs_gbuf
177 * To save much memory, we overlay the table used by compress() with those
178 * used by decompress(). The tab_prefix table is the same size and type as
179 * the codetab. The tab_suffix table needs 2**BITS characters. We get this
180 * from the beginning of htab. The output stack uses the rest of htab, and
181 * contains characters. There is plenty of room for any possible stack
182 * (stack used to be 8000 characters).
185 #define htabof(i) htab[i]
186 #define codetabof(i) codetab[i]
188 #define tab_prefixof(i) codetabof(i)
189 #define tab_suffixof(i) ((char_type *)(htab))[i]
190 #define de_stack ((char_type *)&tab_suffixof(1 << BITS))
192 #define CHECK_GAP 10000 /* Ratio check interval. */
195 * the next two codes should not be changed lightly, as they must not
196 * lie within the contiguous general code space.
198 #define FIRST 257 /* First free entry. */
199 #define CLEAR 256 /* Table clear output code. */
201 static int cl_block(struct s_zstate *);
202 static void cl_hash(struct s_zstate *, count_int);
203 static code_int getcode(struct s_zstate *);
204 static int output(struct s_zstate *, code_int);
205 static int zclose(void *);
206 static int zread(void *, char *, int);
207 static int zwrite(void *, const char *, int);
210 * Algorithm from "A Technique for High Performance Data Compression",
211 * Terry A. Welch, IEEE Computer Vol 17, No 6 (June 1984), pp 8-19.
214 * Modified Lempel-Ziv method (LZW). Basically finds common
215 * substrings and replaces them with a variable size code. This is
216 * deterministic, and can be done on the fly. Thus, the decompression
217 * procedure needs no input table, but tracks the way the table was built.
223 * Algorithm: use open addressing double hashing (no chaining) on the
224 * prefix code / next character combination. We do a variant of Knuth's
225 * algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
226 * secondary probe. Here, the modular division first probe is gives way
227 * to a faster exclusive-or manipulation. Also do block compression with
228 * an adaptive reset, whereby the code table is cleared when the compression
229 * ratio decreases, but after the table fills. The variable-length output
230 * codes are re-sized at this point, and a special CLEAR code is generated
231 * for the decompressor. Late addition: construct the table according to
232 * file size for noticeable speed improvement on small files. Please direct
233 * questions about this implementation to ames!jaw.
236 zwrite(cookie, wbp, num)
254 if (state == S_MIDDLE)
258 maxmaxcode = 1L << maxbits;
259 if (fwrite(magic_header,
260 sizeof(char), sizeof(magic_header), fp) != sizeof(magic_header))
262 tmp = (u_char)((maxbits) | block_compress);
263 if (fwrite(&tmp, sizeof(char), sizeof(tmp), fp) != sizeof(tmp))
267 bytes_out = 3; /* Includes 3-byte header mojo. */
272 checkpoint = CHECK_GAP;
273 maxcode = MAXCODE(n_bits = INIT_BITS);
274 free_ent = ((block_compress) ? FIRST : 256);
280 for (fcode = (long)hsize; fcode < 65536L; fcode *= 2L)
282 hshift = 8 - hshift; /* Set hash code range bound. */
285 cl_hash(zs, (count_int)hsize_reg); /* Clear hash table. */
287 middle: for (i = 0; count--;) {
290 fcode = (long)(((long)c << maxbits) + ent);
291 i = ((c << hshift) ^ ent); /* Xor hashing. */
293 if (htabof(i) == fcode) {
296 } else if ((long)htabof(i) < 0) /* Empty slot. */
298 disp = hsize_reg - i; /* Secondary hash (after G. Knott). */
301 probe: if ((i -= disp) < 0)
304 if (htabof(i) == fcode) {
308 if ((long)htabof(i) >= 0)
310 nomatch: if (output(zs, (code_int) ent) == -1)
314 if (free_ent < maxmaxcode) {
315 codetabof(i) = free_ent++; /* code -> hashtable */
317 } else if ((count_int)in_count >=
318 checkpoint && block_compress) {
319 if (cl_block(zs) == -1)
334 if (zmode == 'w') { /* Put out the final code. */
335 if (output(zs, (code_int) ent) == -1) {
341 if (output(zs, (code_int) - 1) == -1) {
347 rval = fclose(fp) == EOF ? -1 : 0;
353 * Output the given code.
355 * code: A n_bits-bit integer. If == -1, then EOF. This assumes
356 * that n_bits =< (long)wordsize - 1.
358 * Outputs code to the file.
360 * Chars are 8 bits long.
362 * Maintain a BITS character long buffer (so that 8 codes will
363 * fit in it exactly). Use the VAX insv instruction to insert each
364 * code in turn. When the buffer fills up empty it and start over.
367 static char_type lmask[9] =
368 {0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80, 0x00};
369 static char_type rmask[9] =
370 {0x00, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff};
385 /* Get to the first byte. */
389 * Since ocode is always >= 8 bits, only need to mask the first
392 *bp = (*bp & rmask[r_off]) | ((ocode << r_off) & lmask[r_off]);
396 /* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
406 if (offset == (n_bits << 3)) {
410 if (fwrite(bp, sizeof(char), bits, fp) != bits)
417 * If the next entry is going to be too big for the ocode size,
418 * then increase it, if possible.
420 if (free_ent > maxcode || (clear_flg > 0)) {
422 * Write the whole buffer, because the input side won't
423 * discover the size increase until after it has read it.
426 if (fwrite(buf, 1, n_bits, fp) != n_bits)
433 maxcode = MAXCODE(n_bits = INIT_BITS);
437 if (n_bits == maxbits)
438 maxcode = maxmaxcode;
440 maxcode = MAXCODE(n_bits);
444 /* At EOF, write the rest of the buffer. */
446 offset = (offset + 7) / 8;
447 if (fwrite(buf, 1, offset, fp) != offset)
457 * Decompress read. This routine adapts to the codes in the file building
458 * the "string" table on-the-fly; requiring no table to be stored in the
459 * compressed file. The tables used herein are shared with those of the
460 * compress() routine. See the definitions above.
463 zread(cookie, rbp, num)
470 u_char *bp, header[3];
488 /* Check the magic number */
490 sizeof(char), sizeof(header), fp) != sizeof(header) ||
491 memcmp(header, magic_header, sizeof(magic_header)) != 0) {
495 maxbits = header[2]; /* Set -b from file. */
496 block_compress = maxbits & BLOCK_MASK;
498 maxmaxcode = 1L << maxbits;
499 if (maxbits > BITS) {
503 /* As above, initialize the first 256 entries in the table. */
504 maxcode = MAXCODE(n_bits = INIT_BITS);
505 for (code = 255; code >= 0; code--) {
506 tab_prefixof(code) = 0;
507 tab_suffixof(code) = (char_type) code;
509 free_ent = block_compress ? FIRST : 256;
511 finchar = oldcode = getcode(zs);
512 if (oldcode == -1) /* EOF already? */
513 return (0); /* Get out of here */
515 /* First code must be 8 bits = char. */
516 *bp++ = (u_char)finchar;
520 while ((code = getcode(zs)) > -1) {
522 if ((code == CLEAR) && block_compress) {
523 for (code = 255; code >= 0; code--)
524 tab_prefixof(code) = 0;
526 free_ent = FIRST - 1;
527 if ((code = getcode(zs)) == -1) /* O, untimely death! */
532 /* Special case for KwKwK string. */
533 if (code >= free_ent) {
538 /* Generate output characters in reverse order. */
539 while (code >= 256) {
540 *stackp++ = tab_suffixof(code);
541 code = tab_prefixof(code);
543 *stackp++ = finchar = tab_suffixof(code);
545 /* And put them out in forward order. */
550 } while (stackp > de_stack);
552 /* Generate the new entry. */
553 if ((code = free_ent) < maxmaxcode) {
554 tab_prefixof(code) = (u_short) oldcode;
555 tab_suffixof(code) = finchar;
559 /* Remember previous code. */
563 eof: return (num - count);
567 * Read one code from the standard input. If EOF, return -1.
571 * code or -1 is returned.
582 if (clear_flg > 0 || roffset >= size || free_ent > maxcode) {
584 * If the next entry will be too big for the current gcode
585 * size, then we must increase the size. This implies reading
586 * a new buffer full, too.
588 if (free_ent > maxcode) {
590 if (n_bits == maxbits) /* Won't get any bigger now. */
591 maxcode = maxmaxcode;
593 maxcode = MAXCODE(n_bits);
596 maxcode = MAXCODE(n_bits = INIT_BITS);
599 size = fread(gbuf, 1, n_bits, fp);
600 if (size <= 0) /* End of file. */
603 /* Round size down to integral number of codes. */
604 size = (size << 3) - (n_bits - 1);
609 /* Get to the first byte. */
613 /* Get first part (low order bits). */
614 gcode = (*bp++ >> r_off);
616 r_off = 8 - r_off; /* Now, roffset into gcode word. */
618 /* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
620 gcode |= *bp++ << r_off;
625 /* High order bits. */
626 gcode |= (*bp & rmask[bits]) << r_off;
633 cl_block(zs) /* Table clear for block compress. */
638 checkpoint = in_count + CHECK_GAP;
640 if (in_count > 0x007fffff) { /* Shift will overflow. */
641 rat = bytes_out >> 8;
642 if (rat == 0) /* Don't divide by zero. */
645 rat = in_count / rat;
647 rat = (in_count << 8) / bytes_out; /* 8 fractional bits. */
652 cl_hash(zs, (count_int) hsize);
655 if (output(zs, (code_int) CLEAR) == -1)
662 cl_hash(zs, cl_hsize) /* Reset code table. */
670 htab_p = htab + cl_hsize;
672 do { /* Might use Sys V memset(3) here. */
690 } while ((i -= 16) >= 0);
691 for (i += 16; i > 0; i--)
696 zopen(fname, mode, bits)
697 const char *fname, *mode;
702 if ((mode[0] != 'r' && mode[0] != 'w') || mode[1] != '\0' ||
703 bits < 0 || bits > BITS) {
708 if ((zs = calloc(1, sizeof(struct s_zstate))) == NULL)
711 maxbits = bits ? bits : BITS; /* User settable max # bits/code. */
712 maxmaxcode = 1L << maxbits; /* Should NEVER generate this code. */
713 hsize = HSIZE; /* For dynamic table sizing. */
714 free_ent = 0; /* First unused entry. */
715 block_compress = BLOCK_MASK;
718 checkpoint = CHECK_GAP;
719 in_count = 1; /* Length of input. */
720 out_count = 0; /* # of codes output (for debugging). */
726 * Layering compress on top of stdio in order to provide buffering,
727 * and ensure that reads and write work with the data specified.
729 if ((fp = fopen(fname, mode)) == NULL) {
736 return (funopen(zs, zread, NULL, NULL, zclose));
739 return (funopen(zs, NULL, zwrite, NULL, zclose));