1 /* $NetBSD: zopen.c,v 1.16 2022/03/23 11:08:28 andvar Exp $ */
2
3 /*-
4 * Copyright (c) 1985, 1986, 1992, 1993
5 * The Regents of the University of California. All rights reserved.
6 *
7 * This code is derived from software contributed to Berkeley by
8 * Diomidis Spinellis and James A. Woods, derived from original
9 * work by Spencer Thomas and Joseph Orost.
10 *
11 * Redistribution and use in source and binary forms, with or without
12 * modification, are permitted provided that the following conditions
13 * are met:
14 * 1. Redistributions of source code must retain the above copyright
15 * notice, this list of conditions and the following disclaimer.
16 * 2. Redistributions in binary form must reproduce the above copyright
17 * notice, this list of conditions and the following disclaimer in the
18 * documentation and/or other materials provided with the distribution.
19 * 3. Neither the name of the University nor the names of its contributors
20 * may be used to endorse or promote products derived from this software
21 * without specific prior written permission.
22 *
23 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
24 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
25 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
26 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
27 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
28 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
29 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
30 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
31 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
32 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
33 * SUCH DAMAGE.
34 */
35
36 #if defined(LIBC_SCCS) && !defined(lint)
37 #if 0
38 static char sccsid[] = "@(#)zopen.c 8.1 (Berkeley) 6/27/93";
39 #else
40 static char rcsid[] = "$NetBSD: zopen.c,v 1.16 2022/03/23 11:08:28 andvar Exp $";
41 #endif
42 #endif /* LIBC_SCCS and not lint */
43
44 /*-
45 * fcompress.c - File compression ala IEEE Computer, June 1984.
46 *
47 * Compress authors:
48 * Spencer W. Thomas (decvax!utah-cs!thomas)
49 * Jim McKie (decvax!mcvax!jim)
50 * Steve Davies (decvax!vax135!petsd!peora!srd)
51 * Ken Turkowski (decvax!decwrl!turtlevax!ken)
52 * James A. Woods (decvax!ihnp4!ames!jaw)
53 * Joe Orost (decvax!vax135!petsd!joe)
54 *
55 * Cleaned up and converted to library returning I/O streams by
56 * Diomidis Spinellis <dds@doc.ic.ac.uk>.
57 *
58 * zopen(filename, mode, bits)
59 * Returns a FILE * that can be used for read or write. The modes
60 * supported are only "r" and "w". Seeking is not allowed. On
61 * reading the file is decompressed, on writing it is compressed.
62 * The output is compatible with compress(1) with 16 bit tables.
63 * Any file produced by compress(1) can be read.
64 */
65
66 #include <sys/param.h>
67 #include <sys/stat.h>
68
69 #include <errno.h>
70 #include <signal.h>
71 #include <stdio.h>
72 #include <stdlib.h>
73 #include <string.h>
74 #include <unistd.h>
75
76 #define BITS 16 /* Default bits. */
77 #define HSIZE 69001 /* 95% occupancy */
78
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;
82
83 typedef u_char char_type;
84 static char_type magic_header[] =
85 {'\037', '\235'}; /* 1F 9D */
86
87 #define BIT_MASK 0x1f /* Defines for third byte of header. */
88 #define BLOCK_MASK 0x80
89
90 /*
91 * Masks 0x40 and 0x20 are free. I think 0x20 should mean that there is
92 * a fourth header byte (for expansion).
93 */
94 #define INIT_BITS 9 /* Initial number of bits/code. */
95
96 #define MAXCODE(n_bits) ((1 << (n_bits)) - 1)
97
98 struct s_zstate {
99 FILE *zs_fp; /* File stream for I/O */
100 char zs_mode; /* r or w */
101 enum {
102 S_START, S_MIDDLE, S_EOF
103 } zs_state; /* State of computation */
104 int zs_n_bits; /* Number of bits/code. */
105 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. */
112 /*
113 * Block compression parameters -- after all codes are used up,
114 * and compression rate changes, start over.
115 */
116 int zs_block_compress;
117 int zs_clear_flg;
118 long zs_ratio;
119 count_int zs_checkpoint;
120 int zs_offset;
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];
125 union {
126 struct {
127 long zs_fcode;
128 code_int zs_ent;
129 code_int zs_hsize_reg;
130 int zs_hshift;
131 } w; /* Write parameters */
132 struct {
133 char_type *zs_stackp;
134 int zs_finchar;
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 */
139 } u;
140 };
141
142 /* Definitions to retain old variable names */
143 #define fp zs->zs_fp
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
175
176 /*
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).
183 */
184
185 #define htabof(i) htab[i]
186 #define codetabof(i) codetab[i]
187
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))
191
192 #define CHECK_GAP 10000 /* Ratio check interval. */
193
194 /*
195 * the next two codes should not be changed lightly, as they must not
196 * lie within the contiguous general code space.
197 */
198 #define FIRST 257 /* First free entry. */
199 #define CLEAR 256 /* Table clear output code. */
200
201 static int cl_block(struct s_zstate *);
202 static code_int getcode(struct s_zstate *);
203 static int output(struct s_zstate *, code_int);
204 static int zclose(void *);
205 FILE *zopen(const char *, const char *, int);
206 static int zread(void *, char *, int);
207 static int zwrite(void *, const char *, int);
208
209 /*-
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.
212 *
213 * Algorithm:
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.
218 */
219
220 /*-
221 * compress write
222 *
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.
234 */
235 static int
zwrite(void * cookie,const char * wbp,int num)236 zwrite(void *cookie, const char *wbp, int num)
237 {
238 code_int i;
239 int c, disp;
240 struct s_zstate *zs;
241 const u_char *bp;
242 u_char tmp;
243 int count;
244
245 if (num == 0)
246 return (0);
247
248 zs = cookie;
249 count = num;
250 bp = (const u_char *)wbp;
251 if (state == S_MIDDLE)
252 goto middle;
253 state = S_MIDDLE;
254
255 maxmaxcode = 1L << maxbits;
256 if (fwrite(magic_header,
257 sizeof(char), sizeof(magic_header), fp) != sizeof(magic_header))
258 return (-1);
259 tmp = (u_char)(maxbits | block_compress);
260 if (fwrite(&tmp, sizeof(char), sizeof(tmp), fp) != sizeof(tmp))
261 return (-1);
262
263 offset = 0;
264 bytes_out = 3; /* Includes 3-byte header mojo. */
265 out_count = 0;
266 clear_flg = 0;
267 ratio = 0;
268 in_count = 1;
269 checkpoint = CHECK_GAP;
270 maxcode = MAXCODE(n_bits = INIT_BITS);
271 free_ent = ((block_compress) ? FIRST : 256);
272
273 ent = *bp++;
274 --count;
275
276 hshift = 0;
277 for (fcode = (long)hsize; fcode < 65536L; fcode *= 2L)
278 hshift++;
279 hshift = 8 - hshift; /* Set hash code range bound. */
280
281 hsize_reg = hsize;
282 memset(htab, 0xff, hsize_reg * sizeof(count_int));
283
284 middle: while (count--) {
285 c = *bp++;
286 in_count++;
287 fcode = (long)(((long)c << maxbits) + ent);
288 i = ((c << hshift) ^ ent); /* Xor hashing. */
289
290 if (htabof(i) == fcode) {
291 ent = codetabof(i);
292 continue;
293 } else if ((long)htabof(i) < 0) /* Empty slot. */
294 goto nomatch;
295 disp = hsize_reg - i; /* Secondary hash (after G. Knott). */
296 if (i == 0)
297 disp = 1;
298 probe: if ((i -= disp) < 0)
299 i += hsize_reg;
300
301 if (htabof(i) == fcode) {
302 ent = codetabof(i);
303 continue;
304 }
305 if ((long)htabof(i) >= 0)
306 goto probe;
307 nomatch: if (output(zs, (code_int) ent) == -1)
308 return (-1);
309 out_count++;
310 ent = c;
311 if (free_ent < maxmaxcode) {
312 codetabof(i) = free_ent++; /* code -> hashtable */
313 htabof(i) = fcode;
314 } else if ((count_int)in_count >=
315 checkpoint && block_compress) {
316 if (cl_block(zs) == -1)
317 return (-1);
318 }
319 }
320 return (num);
321 }
322
323 static int
zclose(void * cookie)324 zclose(void *cookie)
325 {
326 struct s_zstate *zs;
327 int rval;
328
329 zs = cookie;
330 if (zmode == 'w') { /* Put out the final code. */
331 if (output(zs, (code_int) ent) == -1) {
332 (void)fclose(fp);
333 free(zs);
334 return (-1);
335 }
336 out_count++;
337 if (output(zs, (code_int) - 1) == -1) {
338 (void)fclose(fp);
339 free(zs);
340 return (-1);
341 }
342 }
343 rval = fclose(fp) == EOF ? -1 : 0;
344 free(zs);
345 return (rval);
346 }
347
348 /*-
349 * Output the given code.
350 * Inputs:
351 * code: A n_bits-bit integer. If == -1, then EOF. This assumes
352 * that n_bits =< (long)wordsize - 1.
353 * Outputs:
354 * Outputs code to the file.
355 * Assumptions:
356 * Chars are 8 bits long.
357 * Algorithm:
358 * Maintain a BITS character long buffer (so that 8 codes will
359 * fit in it exactly). Use the VAX insv instruction to insert each
360 * code in turn. When the buffer fills up empty it and start over.
361 */
362
363 static char_type lmask[9] =
364 {0xff, 0xfe, 0xfc, 0xf8, 0xf0, 0xe0, 0xc0, 0x80, 0x00};
365 static char_type rmask[9] =
366 {0x00, 0x01, 0x03, 0x07, 0x0f, 0x1f, 0x3f, 0x7f, 0xff};
367
368 static int
output(struct s_zstate * zs,code_int ocode)369 output(struct s_zstate *zs, code_int ocode)
370 {
371 int bits, r_off;
372 char_type *bp;
373
374 r_off = offset;
375 bits = n_bits;
376 bp = buf;
377 if (ocode >= 0) {
378 /* Get to the first byte. */
379 bp += (r_off >> 3);
380 r_off &= 7;
381 /*
382 * Since ocode is always >= 8 bits, only need to mask the first
383 * hunk on the left.
384 */
385 *bp = (*bp & rmask[r_off]) | ((ocode << r_off) & lmask[r_off]);
386 bp++;
387 bits -= (8 - r_off);
388 ocode >>= 8 - r_off;
389 /* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
390 if (bits >= 8) {
391 *bp++ = ocode;
392 ocode >>= 8;
393 bits -= 8;
394 }
395 /* Last bits. */
396 if (bits)
397 *bp = ocode;
398 offset += n_bits;
399 if (offset == (n_bits << 3)) {
400 bp = buf;
401 bits = n_bits;
402 bytes_out += bits;
403 if (fwrite(bp, sizeof(char), bits, fp) != (size_t)bits)
404 return (-1);
405 bp += bits;
406 bits = 0;
407 offset = 0;
408 }
409 /*
410 * If the next entry is going to be too big for the ocode size,
411 * then increase it, if possible.
412 */
413 if (free_ent > maxcode || (clear_flg > 0)) {
414 /*
415 * Write the whole buffer, because the input side won't
416 * discover the size increase until after it has read it.
417 */
418 if (offset > 0) {
419 if (fwrite(buf, 1, n_bits, fp) != (size_t)n_bits)
420 return (-1);
421 bytes_out += n_bits;
422 }
423 offset = 0;
424
425 if (clear_flg) {
426 maxcode = MAXCODE(n_bits = INIT_BITS);
427 clear_flg = 0;
428 } else {
429 n_bits++;
430 if (n_bits == maxbits)
431 maxcode = maxmaxcode;
432 else
433 maxcode = MAXCODE(n_bits);
434 }
435 }
436 } else {
437 /* At EOF, write the rest of the buffer. */
438 if (offset > 0) {
439 offset = (offset + 7) / 8;
440 if (fwrite(buf, 1, offset, fp) != (size_t)offset)
441 return (-1);
442 bytes_out += offset;
443 }
444 offset = 0;
445 }
446 return (0);
447 }
448
449 /*
450 * Decompress read. This routine adapts to the codes in the file building
451 * the "string" table on-the-fly; requiring no table to be stored in the
452 * compressed file. The tables used herein are shared with those of the
453 * compress() routine. See the definitions above.
454 */
455 static int
zread(void * cookie,char * rbp,int num)456 zread(void *cookie, char *rbp, int num)
457 {
458 u_int count;
459 struct s_zstate *zs;
460 u_char *bp, header[3];
461
462 if (num == 0)
463 return (0);
464
465 zs = cookie;
466 count = num;
467 bp = (u_char *)rbp;
468 switch (state) {
469 case S_START:
470 state = S_MIDDLE;
471 break;
472 case S_MIDDLE:
473 goto middle;
474 case S_EOF:
475 goto eof;
476 }
477
478 /* Check the magic number */
479 if (fread(header,
480 sizeof(char), sizeof(header), fp) != sizeof(header) ||
481 memcmp(header, magic_header, sizeof(magic_header)) != 0) {
482 errno = EFTYPE;
483 return (-1);
484 }
485 maxbits = header[2]; /* Set -b from file. */
486 block_compress = maxbits & BLOCK_MASK;
487 maxbits &= BIT_MASK;
488 maxmaxcode = 1L << maxbits;
489 if (maxbits > BITS || maxbits < 12) {
490 errno = EFTYPE;
491 return (-1);
492 }
493 /* As above, initialize the first 256 entries in the table. */
494 maxcode = MAXCODE(n_bits = INIT_BITS);
495 for (code = 255; code >= 0; code--) {
496 tab_prefixof(code) = 0;
497 tab_suffixof(code) = (char_type) code;
498 }
499 free_ent = block_compress ? FIRST : 256;
500 oldcode = -1;
501 stackp = de_stack;
502
503 while ((code = getcode(zs)) > -1) {
504
505 if ((code == CLEAR) && block_compress) {
506 for (code = 255; code >= 0; code--)
507 tab_prefixof(code) = 0;
508 clear_flg = 1;
509 free_ent = FIRST;
510 oldcode = -1;
511 continue;
512 }
513 incode = code;
514
515 /* Special case for kWkWk string. */
516 if (code >= free_ent) {
517 if (code > free_ent || oldcode == -1) {
518 /* Bad stream. */
519 errno = EINVAL;
520 return (-1);
521 }
522 *stackp++ = finchar;
523 code = oldcode;
524 }
525 /*
526 * The above condition ensures that code < free_ent.
527 * The construction of tab_prefixof in turn guarantees that
528 * each iteration decreases code and therefore stack usage is
529 * bound by 1 << BITS - 256.
530 */
531
532 /* Generate output characters in reverse order. */
533 while (code >= 256) {
534 *stackp++ = tab_suffixof(code);
535 code = tab_prefixof(code);
536 }
537 *stackp++ = finchar = tab_suffixof(code);
538
539 /* And put them out in forward order. */
540 middle: do {
541 if (count-- == 0)
542 return (num);
543 *bp++ = *--stackp;
544 } while (stackp > de_stack);
545
546 /* Generate the new entry. */
547 if ((code = free_ent) < maxmaxcode && oldcode != -1) {
548 tab_prefixof(code) = (u_short) oldcode;
549 tab_suffixof(code) = finchar;
550 free_ent = code + 1;
551 }
552
553 /* Remember previous code. */
554 oldcode = incode;
555 }
556 state = S_EOF;
557 eof: return (num - count);
558 }
559
560 /*-
561 * Read one code from the standard input. If EOF, return -1.
562 * Inputs:
563 * stdin
564 * Outputs:
565 * code or -1 is returned.
566 */
567 static code_int
getcode(struct s_zstate * zs)568 getcode(struct s_zstate *zs)
569 {
570 code_int gcode;
571 int r_off, bits;
572 char_type *bp;
573
574 bp = gbuf;
575 if (clear_flg > 0 || roffset >= size || free_ent > maxcode) {
576 /*
577 * If the next entry will be too big for the current gcode
578 * size, then we must increase the size. This implies reading
579 * a new buffer full, too.
580 */
581 if (free_ent > maxcode) {
582 n_bits++;
583 if (n_bits == maxbits) /* Won't get any bigger now. */
584 maxcode = maxmaxcode;
585 else
586 maxcode = MAXCODE(n_bits);
587 }
588 if (clear_flg > 0) {
589 maxcode = MAXCODE(n_bits = INIT_BITS);
590 clear_flg = 0;
591 }
592 size = fread(gbuf, 1, n_bits, fp);
593 if (size <= 0) /* End of file. */
594 return (-1);
595 roffset = 0;
596 /* Round size down to integral number of codes. */
597 size = (size << 3) - (n_bits - 1);
598 }
599 r_off = roffset;
600 bits = n_bits;
601
602 /* Get to the first byte. */
603 bp += (r_off >> 3);
604 r_off &= 7;
605
606 /* Get first part (low order bits). */
607 gcode = (*bp++ >> r_off);
608 bits -= (8 - r_off);
609 r_off = 8 - r_off; /* Now, roffset into gcode word. */
610
611 /* Get any 8 bit parts in the middle (<=1 for up to 16 bits). */
612 if (bits >= 8) {
613 gcode |= *bp++ << r_off;
614 r_off += 8;
615 bits -= 8;
616 }
617
618 /* High order bits. */
619 gcode |= (*bp & rmask[bits]) << r_off;
620 roffset += n_bits;
621
622 return (gcode);
623 }
624
625 static int
cl_block(struct s_zstate * zs)626 cl_block(struct s_zstate *zs) /* Table clear for block compress. */
627 {
628 long rat;
629
630 checkpoint = in_count + CHECK_GAP;
631
632 if (in_count > 0x007fffff) { /* Shift will overflow. */
633 rat = bytes_out >> 8;
634 if (rat == 0) /* Don't divide by zero. */
635 rat = 0x7fffffff;
636 else
637 rat = in_count / rat;
638 } else
639 rat = (in_count << 8) / bytes_out; /* 8 fractional bits. */
640 if (rat > ratio)
641 ratio = rat;
642 else {
643 ratio = 0;
644 memset(htab, 0xff, hsize * sizeof(count_int));
645 free_ent = FIRST;
646 clear_flg = 1;
647 if (output(zs, (code_int) CLEAR) == -1)
648 return (-1);
649 }
650 return (0);
651 }
652
653 FILE *
zopen(const char * fname,const char * mode,int bits)654 zopen(const char *fname, const char *mode, int bits)
655 {
656 struct s_zstate *zs;
657
658 if ((mode[0] != 'r' && mode[0] != 'w') || mode[1] != '\0' ||
659 bits < 0 || bits > BITS) {
660 errno = EINVAL;
661 return (NULL);
662 }
663
664 if ((zs = calloc(1, sizeof(struct s_zstate))) == NULL)
665 return (NULL);
666
667 maxbits = bits ? bits : BITS; /* User settable max # bits/code. */
668 maxmaxcode = 1 << maxbits; /* Should NEVER generate this code. */
669 hsize = HSIZE; /* For dynamic table sizing. */
670 free_ent = 0; /* First unused entry. */
671 block_compress = BLOCK_MASK;
672 clear_flg = 0;
673 ratio = 0;
674 checkpoint = CHECK_GAP;
675 in_count = 1; /* Length of input. */
676 out_count = 0; /* # of codes output (for debugging). */
677 state = S_START;
678 roffset = 0;
679 size = 0;
680
681 /*
682 * Layering compress on top of stdio in order to provide buffering,
683 * and ensure that reads and write work with the data specified.
684 */
685 if ((fp = fopen(fname, mode)) == NULL) {
686 free(zs);
687 return (NULL);
688 }
689 switch (*mode) {
690 case 'r':
691 zmode = 'r';
692 return (funopen(zs, zread, NULL, NULL, zclose));
693 case 'w':
694 zmode = 'w';
695 return (funopen(zs, NULL, zwrite, NULL, zclose));
696 }
697 /* NOTREACHED */
698 return (NULL);
699 }
700