xref: /freebsd/contrib/sendmail/libsm/vfscanf.c (revision 2a4a1db342263067035ce69a4017c645da63455d)
1 /*
2  * Copyright (c) 2000-2001 Sendmail, Inc. and its suppliers.
3  *      All rights reserved.
4  * Copyright (c) 1990, 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  * Chris Torek.
9  *
10  * By using this file, you agree to the terms and conditions set
11  * forth in the LICENSE file which can be found at the top level of
12  * the sendmail distribution.
13  */
14 
15 #include <sm/gen.h>
16 SM_IDSTR(id, "@(#)$Id: vfscanf.c,v 1.1.1.1 2002/02/17 21:56:43 gshapiro Exp $")
17 
18 #include <ctype.h>
19 #include <stdlib.h>
20 #include <errno.h>
21 #include <setjmp.h>
22 #include <sys/time.h>
23 #include <sm/varargs.h>
24 #include <sm/config.h>
25 #include <sm/io.h>
26 #include <sm/signal.h>
27 #include <sm/clock.h>
28 #include <sm/string.h>
29 #include "local.h"
30 
31 #define BUF		513	/* Maximum length of numeric string. */
32 
33 /* Flags used during conversion. */
34 #define LONG		0x01	/* l: long or double */
35 #define SHORT		0x04	/* h: short */
36 #define QUAD		0x08	/* q: quad (same as ll) */
37 #define SUPPRESS	0x10	/* suppress assignment */
38 #define POINTER		0x20	/* weird %p pointer (`fake hex') */
39 #define NOSKIP		0x40	/* do not skip blanks */
40 
41 /*
42 **  The following are used in numeric conversions only:
43 **  SIGNOK, NDIGITS, DPTOK, and EXPOK are for floating point;
44 **  SIGNOK, NDIGITS, PFXOK, and NZDIGITS are for integral.
45 */
46 
47 #define SIGNOK		0x080	/* +/- is (still) legal */
48 #define NDIGITS		0x100	/* no digits detected */
49 
50 #define DPTOK		0x200	/* (float) decimal point is still legal */
51 #define EXPOK		0x400	/* (float) exponent (e+3, etc) still legal */
52 
53 #define PFXOK		0x200	/* 0x prefix is (still) legal */
54 #define NZDIGITS	0x400	/* no zero digits detected */
55 
56 /* Conversion types. */
57 #define CT_CHAR		0	/* %c conversion */
58 #define CT_CCL		1	/* %[...] conversion */
59 #define CT_STRING	2	/* %s conversion */
60 #define CT_INT		3	/* integer, i.e., strtoll or strtoull */
61 #define CT_FLOAT	4	/* floating, i.e., strtod */
62 
63 static unsigned char *sm_sccl __P((char *, unsigned char *));
64 static jmp_buf ScanTimeOut;
65 
66 /*
67 **  SCANALRM -- handler when timeout activated for sm_io_vfscanf()
68 **
69 **  Returns flow of control to where setjmp(ScanTimeOut) was set.
70 **
71 **	Parameters:
72 **		sig -- unused
73 **
74 **	Returns:
75 **		does not return
76 **
77 **	Side Effects:
78 **		returns flow of control to setjmp(ScanTimeOut).
79 **
80 **	NOTE:	THIS CAN BE CALLED FROM A SIGNAL HANDLER.  DO NOT ADD
81 **		ANYTHING TO THIS ROUTINE UNLESS YOU KNOW WHAT YOU ARE
82 **		DOING.
83 */
84 
85 /* ARGSUSED0 */
86 static void
87 scanalrm(sig)
88 	int sig;
89 {
90 	longjmp(ScanTimeOut, 1);
91 }
92 
93 /*
94 **  SM_VFSCANF -- convert input into data units
95 **
96 **	Parameters:
97 **		fp -- file pointer for input data
98 **		timeout -- time intvl allowed to complete (milliseconds)
99 **		fmt0 -- format for finding data units
100 **		ap -- vectors for memory location for storing data units
101 **
102 **	Results:
103 **		Success: number of data units assigned
104 **		Failure: SM_IO_EOF
105 */
106 
107 int
108 sm_vfscanf(fp, timeout, fmt0, ap)
109 	register SM_FILE_T *fp;
110 	int SM_NONVOLATILE timeout;
111 	char const *fmt0;
112 	va_list SM_NONVOLATILE ap;
113 {
114 	register unsigned char *SM_NONVOLATILE fmt = (unsigned char *) fmt0;
115 	register int c;		/* character from format, or conversion */
116 	register size_t width;	/* field width, or 0 */
117 	register char *p;	/* points into all kinds of strings */
118 	register int n;		/* handy integer */
119 	register int flags;	/* flags as defined above */
120 	register char *p0;	/* saves original value of p when necessary */
121 	int nassigned;		/* number of fields assigned */
122 	int nread;		/* number of characters consumed from fp */
123 	int base;		/* base argument to strtoll/strtoull */
124 	ULONGLONG_T (*ccfn)();	/* conversion function (strtoll/strtoull) */
125 	char ccltab[256];	/* character class table for %[...] */
126 	char buf[BUF];		/* buffer for numeric conversions */
127 	SM_EVENT *evt = NULL;
128 
129 	/* `basefix' is used to avoid `if' tests in the integer scanner */
130 	static short basefix[17] =
131 		{ 10, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 };
132 
133 	if (timeout == SM_TIME_DEFAULT)
134 		timeout = fp->f_timeout;
135 	if (timeout == SM_TIME_IMMEDIATE)
136 	{
137 		/*
138 		**  Filling the buffer will take time and we are wanted to
139 		**  return immediately. So...
140 		*/
141 
142 		errno = EAGAIN;
143 		return SM_IO_EOF;
144 	}
145 
146 	if (timeout != SM_TIME_FOREVER)
147 	{
148 		if (setjmp(ScanTimeOut) != 0)
149 		{
150 			errno = EAGAIN;
151 			return SM_IO_EOF;
152 		}
153 
154 		evt = sm_seteventm(timeout, scanalrm, 0);
155 	}
156 
157 	nassigned = 0;
158 	nread = 0;
159 	base = 0;		/* XXX just to keep gcc happy */
160 	ccfn = NULL;		/* XXX just to keep gcc happy */
161 	for (;;)
162 	{
163 		c = *fmt++;
164 		if (c == 0)
165 		{
166 			if (evt != NULL)
167 				sm_clrevent(evt); /*  undo our timeout */
168 			return nassigned;
169 		}
170 		if (isspace(c))
171 		{
172 			while ((fp->f_r > 0 || sm_refill(fp, SM_TIME_FOREVER)
173 						== 0) &&
174 			    isspace(*fp->f_p))
175 				nread++, fp->f_r--, fp->f_p++;
176 			continue;
177 		}
178 		if (c != '%')
179 			goto literal;
180 		width = 0;
181 		flags = 0;
182 
183 		/*
184 		**  switch on the format.  continue if done;
185 		**  break once format type is derived.
186 		*/
187 
188 again:		c = *fmt++;
189 		switch (c)
190 		{
191 		  case '%':
192 literal:
193 			if (fp->f_r <= 0 && sm_refill(fp, SM_TIME_FOREVER))
194 				goto input_failure;
195 			if (*fp->f_p != c)
196 				goto match_failure;
197 			fp->f_r--, fp->f_p++;
198 			nread++;
199 			continue;
200 
201 		  case '*':
202 			flags |= SUPPRESS;
203 			goto again;
204 		  case 'h':
205 			flags |= SHORT;
206 			goto again;
207 		  case 'l':
208 			if (*fmt == 'l')
209 			{
210 				fmt++;
211 				flags |= QUAD;
212 			}
213 			else
214 			{
215 				flags |= LONG;
216 			}
217 			goto again;
218 		  case 'q':
219 			flags |= QUAD;
220 			goto again;
221 
222 		  case '0': case '1': case '2': case '3': case '4':
223 		  case '5': case '6': case '7': case '8': case '9':
224 			width = width * 10 + c - '0';
225 			goto again;
226 
227 		/*
228 		**  Conversions.
229 		**  Those marked `compat' are for 4.[123]BSD compatibility.
230 		**
231 		**  (According to ANSI, E and X formats are supposed
232 		**  to the same as e and x.  Sorry about that.)
233 		*/
234 
235 		  case 'D':	/* compat */
236 			flags |= LONG;
237 			/* FALLTHROUGH */
238 		  case 'd':
239 			c = CT_INT;
240 			ccfn = (ULONGLONG_T (*)())sm_strtoll;
241 			base = 10;
242 			break;
243 
244 		  case 'i':
245 			c = CT_INT;
246 			ccfn = (ULONGLONG_T (*)())sm_strtoll;
247 			base = 0;
248 			break;
249 
250 		  case 'O':	/* compat */
251 			flags |= LONG;
252 			/* FALLTHROUGH */
253 		  case 'o':
254 			c = CT_INT;
255 			ccfn = sm_strtoull;
256 			base = 8;
257 			break;
258 
259 		  case 'u':
260 			c = CT_INT;
261 			ccfn = sm_strtoull;
262 			base = 10;
263 			break;
264 
265 		  case 'X':
266 		  case 'x':
267 			flags |= PFXOK;	/* enable 0x prefixing */
268 			c = CT_INT;
269 			ccfn = sm_strtoull;
270 			base = 16;
271 			break;
272 
273 		  case 'E':
274 		  case 'G':
275 		  case 'e':
276 		  case 'f':
277 		  case 'g':
278 			c = CT_FLOAT;
279 			break;
280 
281 		  case 's':
282 			c = CT_STRING;
283 			break;
284 
285 		  case '[':
286 			fmt = sm_sccl(ccltab, fmt);
287 			flags |= NOSKIP;
288 			c = CT_CCL;
289 			break;
290 
291 		  case 'c':
292 			flags |= NOSKIP;
293 			c = CT_CHAR;
294 			break;
295 
296 		  case 'p':	/* pointer format is like hex */
297 			flags |= POINTER | PFXOK;
298 			c = CT_INT;
299 			ccfn = sm_strtoull;
300 			base = 16;
301 			break;
302 
303 		  case 'n':
304 			if (flags & SUPPRESS)	/* ??? */
305 				continue;
306 			if (flags & SHORT)
307 				*SM_VA_ARG(ap, short *) = nread;
308 			else if (flags & LONG)
309 				*SM_VA_ARG(ap, long *) = nread;
310 			else
311 				*SM_VA_ARG(ap, int *) = nread;
312 			continue;
313 
314 		/* Disgusting backwards compatibility hacks.	XXX */
315 		  case '\0':	/* compat */
316 			if (evt != NULL)
317 				sm_clrevent(evt); /*  undo our timeout */
318 			return SM_IO_EOF;
319 
320 		  default:	/* compat */
321 			if (isupper(c))
322 				flags |= LONG;
323 			c = CT_INT;
324 			ccfn = (ULONGLONG_T (*)()) sm_strtoll;
325 			base = 10;
326 			break;
327 		}
328 
329 		/* We have a conversion that requires input. */
330 		if (fp->f_r <= 0 && sm_refill(fp, SM_TIME_FOREVER))
331 			goto input_failure;
332 
333 		/*
334 		**  Consume leading white space, except for formats
335 		**  that suppress this.
336 		*/
337 
338 		if ((flags & NOSKIP) == 0)
339 		{
340 			while (isspace(*fp->f_p))
341 			{
342 				nread++;
343 				if (--fp->f_r > 0)
344 					fp->f_p++;
345 				else if (sm_refill(fp, SM_TIME_FOREVER))
346 					goto input_failure;
347 			}
348 			/*
349 			**  Note that there is at least one character in
350 			**  the buffer, so conversions that do not set NOSKIP
351 			**  can no longer result in an input failure.
352 			*/
353 		}
354 
355 		/* Do the conversion. */
356 		switch (c)
357 		{
358 		  case CT_CHAR:
359 			/* scan arbitrary characters (sets NOSKIP) */
360 			if (width == 0)
361 				width = 1;
362 			if (flags & SUPPRESS)
363 			{
364 				size_t sum = 0;
365 				for (;;)
366 				{
367 					if ((size_t) (n = fp->f_r) < width)
368 					{
369 						sum += n;
370 						width -= n;
371 						fp->f_p += n;
372 						if (sm_refill(fp,
373 							      SM_TIME_FOREVER))
374 						{
375 							if (sum == 0)
376 								goto input_failure;
377 							break;
378 						}
379 					}
380 					else
381 					{
382 						sum += width;
383 						fp->f_r -= width;
384 						fp->f_p += width;
385 						break;
386 					}
387 				}
388 				nread += sum;
389 			}
390 			else
391 			{
392 				size_t r;
393 
394 				r = sm_io_read(fp, SM_TIME_FOREVER,
395 						(void *) SM_VA_ARG(ap, char *),
396 						width);
397 				if (r == 0)
398 					goto input_failure;
399 				nread += r;
400 				nassigned++;
401 			}
402 			break;
403 
404 		  case CT_CCL:
405 			/* scan a (nonempty) character class (sets NOSKIP) */
406 			if (width == 0)
407 				width = (size_t)~0;	/* `infinity' */
408 
409 			/* take only those things in the class */
410 			if (flags & SUPPRESS)
411 			{
412 				n = 0;
413 				while (ccltab[*fp->f_p] != '\0')
414 				{
415 					n++, fp->f_r--, fp->f_p++;
416 					if (--width == 0)
417 						break;
418 					if (fp->f_r <= 0 &&
419 					    sm_refill(fp, SM_TIME_FOREVER))
420 					{
421 						if (n == 0) /* XXX how? */
422 							goto input_failure;
423 						break;
424 					}
425 				}
426 				if (n == 0)
427 					goto match_failure;
428 			}
429 			else
430 			{
431 				p0 = p = SM_VA_ARG(ap, char *);
432 				while (ccltab[*fp->f_p] != '\0')
433 				{
434 					fp->f_r--;
435 					*p++ = *fp->f_p++;
436 					if (--width == 0)
437 						break;
438 					if (fp->f_r <= 0 &&
439 					    sm_refill(fp, SM_TIME_FOREVER))
440 					{
441 						if (p == p0)
442 							goto input_failure;
443 						break;
444 					}
445 				}
446 				n = p - p0;
447 				if (n == 0)
448 					goto match_failure;
449 				*p = 0;
450 				nassigned++;
451 			}
452 			nread += n;
453 			break;
454 
455 		  case CT_STRING:
456 			/* like CCL, but zero-length string OK, & no NOSKIP */
457 			if (width == 0)
458 				width = (size_t)~0;
459 			if (flags & SUPPRESS)
460 			{
461 				n = 0;
462 				while (!isspace(*fp->f_p))
463 				{
464 					n++, fp->f_r--, fp->f_p++;
465 					if (--width == 0)
466 						break;
467 					if (fp->f_r <= 0 &&
468 					    sm_refill(fp, SM_TIME_FOREVER))
469 						break;
470 				}
471 				nread += n;
472 			}
473 			else
474 			{
475 				p0 = p = SM_VA_ARG(ap, char *);
476 				while (!isspace(*fp->f_p))
477 				{
478 					fp->f_r--;
479 					*p++ = *fp->f_p++;
480 					if (--width == 0)
481 						break;
482 					if (fp->f_r <= 0 &&
483 					    sm_refill(fp, SM_TIME_FOREVER))
484 						break;
485 				}
486 				*p = 0;
487 				nread += p - p0;
488 				nassigned++;
489 			}
490 			continue;
491 
492 		  case CT_INT:
493 			/* scan an integer as if by strtoll/strtoull */
494 #if SM_CONF_BROKEN_SIZE_T
495 			if (width == 0 || width > sizeof(buf) - 1)
496 				width = sizeof(buf) - 1;
497 #else /* SM_CONF_BROKEN_SIZE_T */
498 			/* size_t is unsigned, hence this optimisation */
499 			if (--width > sizeof(buf) - 2)
500 				width = sizeof(buf) - 2;
501 			width++;
502 #endif /* SM_CONF_BROKEN_SIZE_T */
503 			flags |= SIGNOK | NDIGITS | NZDIGITS;
504 			for (p = buf; width > 0; width--)
505 			{
506 				c = *fp->f_p;
507 
508 				/*
509 				**  Switch on the character; `goto ok'
510 				**  if we accept it as a part of number.
511 				*/
512 
513 				switch (c)
514 				{
515 
516 				/*
517 				**  The digit 0 is always legal, but is
518 				**  special.  For %i conversions, if no
519 				**  digits (zero or nonzero) have been
520 				**  scanned (only signs), we will have
521 				**  base==0.  In that case, we should set
522 				**  it to 8 and enable 0x prefixing.
523 				**  Also, if we have not scanned zero digits
524 				**  before this, do not turn off prefixing
525 				**  (someone else will turn it off if we
526 				**  have scanned any nonzero digits).
527 				*/
528 
529 				  case '0':
530 					if (base == 0)
531 					{
532 						base = 8;
533 						flags |= PFXOK;
534 					}
535 					if (flags & NZDIGITS)
536 					    flags &= ~(SIGNOK|NZDIGITS|NDIGITS);
537 					else
538 					    flags &= ~(SIGNOK|PFXOK|NDIGITS);
539 					goto ok;
540 
541 				/* 1 through 7 always legal */
542 				  case '1': case '2': case '3':
543 				  case '4': case '5': case '6': case '7':
544 					base = basefix[base];
545 					flags &= ~(SIGNOK | PFXOK | NDIGITS);
546 					goto ok;
547 
548 				/* digits 8 and 9 ok iff decimal or hex */
549 				  case '8': case '9':
550 					base = basefix[base];
551 					if (base <= 8)
552 						break;	/* not legal here */
553 					flags &= ~(SIGNOK | PFXOK | NDIGITS);
554 					goto ok;
555 
556 				/* letters ok iff hex */
557 				  case 'A': case 'B': case 'C':
558 				  case 'D': case 'E': case 'F':
559 				  case 'a': case 'b': case 'c':
560 				  case 'd': case 'e': case 'f':
561 
562 					/* no need to fix base here */
563 					if (base <= 10)
564 						break;	/* not legal here */
565 					flags &= ~(SIGNOK | PFXOK | NDIGITS);
566 					goto ok;
567 
568 				/* sign ok only as first character */
569 				  case '+': case '-':
570 					if (flags & SIGNOK)
571 					{
572 						flags &= ~SIGNOK;
573 						goto ok;
574 					}
575 					break;
576 
577 				/* x ok iff flag still set & 2nd char */
578 				  case 'x': case 'X':
579 					if (flags & PFXOK && p == buf + 1)
580 					{
581 						base = 16;	/* if %i */
582 						flags &= ~PFXOK;
583 						goto ok;
584 					}
585 					break;
586 				}
587 
588 				/*
589 				**  If we got here, c is not a legal character
590 				**  for a number.  Stop accumulating digits.
591 				*/
592 
593 				break;
594 		ok:
595 				/* c is legal: store it and look at the next. */
596 				*p++ = c;
597 				if (--fp->f_r > 0)
598 					fp->f_p++;
599 				else if (sm_refill(fp, SM_TIME_FOREVER))
600 					break;		/* SM_IO_EOF */
601 			}
602 
603 			/*
604 			**  If we had only a sign, it is no good; push
605 			**  back the sign.  If the number ends in `x',
606 			**  it was [sign] '0' 'x', so push back the x
607 			**  and treat it as [sign] '0'.
608 			*/
609 
610 			if (flags & NDIGITS)
611 			{
612 				if (p > buf)
613 					(void) sm_io_ungetc(fp, SM_TIME_DEFAULT,
614 							    *(unsigned char *)--p);
615 				goto match_failure;
616 			}
617 			c = ((unsigned char *)p)[-1];
618 			if (c == 'x' || c == 'X')
619 			{
620 				--p;
621 				(void) sm_io_ungetc(fp, SM_TIME_DEFAULT, c);
622 			}
623 			if ((flags & SUPPRESS) == 0)
624 			{
625 				ULONGLONG_T res;
626 
627 				*p = 0;
628 				res = (*ccfn)(buf, (char **)NULL, base);
629 				if (flags & POINTER)
630 					*SM_VA_ARG(ap, void **) =
631 					    (void *)(long) res;
632 				else if (flags & QUAD)
633 					*SM_VA_ARG(ap, LONGLONG_T *) = res;
634 				else if (flags & LONG)
635 					*SM_VA_ARG(ap, long *) = res;
636 				else if (flags & SHORT)
637 					*SM_VA_ARG(ap, short *) = res;
638 				else
639 					*SM_VA_ARG(ap, int *) = res;
640 				nassigned++;
641 			}
642 			nread += p - buf;
643 			break;
644 
645 		  case CT_FLOAT:
646 			/* scan a floating point number as if by strtod */
647 			if (width == 0 || width > sizeof(buf) - 1)
648 				width = sizeof(buf) - 1;
649 			flags |= SIGNOK | NDIGITS | DPTOK | EXPOK;
650 			for (p = buf; width; width--)
651 			{
652 				c = *fp->f_p;
653 
654 				/*
655 				**  This code mimicks the integer conversion
656 				**  code, but is much simpler.
657 				*/
658 
659 				switch (c)
660 				{
661 
662 				  case '0': case '1': case '2': case '3':
663 				  case '4': case '5': case '6': case '7':
664 				  case '8': case '9':
665 					flags &= ~(SIGNOK | NDIGITS);
666 					goto fok;
667 
668 				  case '+': case '-':
669 					if (flags & SIGNOK)
670 					{
671 						flags &= ~SIGNOK;
672 						goto fok;
673 					}
674 					break;
675 				  case '.':
676 					if (flags & DPTOK)
677 					{
678 						flags &= ~(SIGNOK | DPTOK);
679 						goto fok;
680 					}
681 					break;
682 				  case 'e': case 'E':
683 
684 					/* no exponent without some digits */
685 					if ((flags&(NDIGITS|EXPOK)) == EXPOK)
686 					{
687 						flags =
688 						    (flags & ~(EXPOK|DPTOK)) |
689 						    SIGNOK | NDIGITS;
690 						goto fok;
691 					}
692 					break;
693 				}
694 				break;
695 		fok:
696 				*p++ = c;
697 				if (--fp->f_r > 0)
698 					fp->f_p++;
699 				else if (sm_refill(fp, SM_TIME_FOREVER))
700 					break;	/* SM_IO_EOF */
701 			}
702 
703 			/*
704 			**  If no digits, might be missing exponent digits
705 			**  (just give back the exponent) or might be missing
706 			**  regular digits, but had sign and/or decimal point.
707 			*/
708 
709 			if (flags & NDIGITS)
710 			{
711 				if (flags & EXPOK)
712 				{
713 					/* no digits at all */
714 					while (p > buf)
715 						(void) sm_io_ungetc(fp,
716 							     SM_TIME_DEFAULT,
717 							     *(unsigned char *)--p);
718 					goto match_failure;
719 				}
720 
721 				/* just a bad exponent (e and maybe sign) */
722 				c = *(unsigned char *) --p;
723 				if (c != 'e' && c != 'E')
724 				{
725 					(void) sm_io_ungetc(fp, SM_TIME_DEFAULT,
726 							    c); /* sign */
727 					c = *(unsigned char *)--p;
728 				}
729 				(void) sm_io_ungetc(fp, SM_TIME_DEFAULT, c);
730 			}
731 			if ((flags & SUPPRESS) == 0)
732 			{
733 				double res;
734 
735 				*p = 0;
736 				res = strtod(buf, (char **) NULL);
737 				if (flags & LONG)
738 					*SM_VA_ARG(ap, double *) = res;
739 				else
740 					*SM_VA_ARG(ap, float *) = res;
741 				nassigned++;
742 			}
743 			nread += p - buf;
744 			break;
745 		}
746 	}
747 input_failure:
748 	if (evt != NULL)
749 		sm_clrevent(evt); /*  undo our timeout */
750 	return nassigned ? nassigned : -1;
751 match_failure:
752 	if (evt != NULL)
753 		sm_clrevent(evt); /*  undo our timeout */
754 	return nassigned;
755 }
756 
757 /*
758 **  SM_SCCL -- sequenced character comparison list
759 **
760 **  Fill in the given table from the scanset at the given format
761 **  (just after `[').  Return a pointer to the character past the
762 **  closing `]'.  The table has a 1 wherever characters should be
763 **  considered part of the scanset.
764 **
765 **	Parameters:
766 **		tab -- array flagging "active" char's to match (returned)
767 **		fmt -- character list (within "[]")
768 **
769 **	Results:
770 */
771 
772 static unsigned char *
773 sm_sccl(tab, fmt)
774 	register char *tab;
775 	register unsigned char *fmt;
776 {
777 	register int c, n, v;
778 
779 	/* first `clear' the whole table */
780 	c = *fmt++;		/* first char hat => negated scanset */
781 	if (c == '^')
782 	{
783 		v = 1;		/* default => accept */
784 		c = *fmt++;	/* get new first char */
785 	}
786 	else
787 		v = 0;		/* default => reject */
788 
789 	/* should probably use memset here */
790 	for (n = 0; n < 256; n++)
791 		tab[n] = v;
792 	if (c == 0)
793 		return fmt - 1;	/* format ended before closing ] */
794 
795 	/*
796 	**  Now set the entries corresponding to the actual scanset
797 	**  to the opposite of the above.
798 	**
799 	**  The first character may be ']' (or '-') without being special;
800 	**  the last character may be '-'.
801 	*/
802 
803 	v = 1 - v;
804 	for (;;)
805 	{
806 		tab[c] = v;		/* take character c */
807 doswitch:
808 		n = *fmt++;		/* and examine the next */
809 		switch (n)
810 		{
811 
812 		  case 0:			/* format ended too soon */
813 			return fmt - 1;
814 
815 		  case '-':
816 			/*
817 			**  A scanset of the form
818 			**	[01+-]
819 			**  is defined as `the digit 0, the digit 1,
820 			**  the character +, the character -', but
821 			**  the effect of a scanset such as
822 			**	[a-zA-Z0-9]
823 			**  is implementation defined.  The V7 Unix
824 			**  scanf treats `a-z' as `the letters a through
825 			**  z', but treats `a-a' as `the letter a, the
826 			**  character -, and the letter a'.
827 			**
828 			**  For compatibility, the `-' is not considerd
829 			**  to define a range if the character following
830 			**  it is either a close bracket (required by ANSI)
831 			**  or is not numerically greater than the character
832 			**  we just stored in the table (c).
833 			*/
834 
835 			n = *fmt;
836 			if (n == ']' || n < c)
837 			{
838 				c = '-';
839 				break;	/* resume the for(;;) */
840 			}
841 			fmt++;
842 			do
843 			{
844 				/* fill in the range */
845 				tab[++c] = v;
846 			} while (c < n);
847 #if 1	/* XXX another disgusting compatibility hack */
848 
849 			/*
850 			**  Alas, the V7 Unix scanf also treats formats
851 			**  such as [a-c-e] as `the letters a through e'.
852 			**  This too is permitted by the standard....
853 			*/
854 
855 			goto doswitch;
856 #else
857 			c = *fmt++;
858 			if (c == 0)
859 				return fmt - 1;
860 			if (c == ']')
861 				return fmt;
862 			break;
863 #endif
864 
865 		  case ']':		/* end of scanset */
866 			return fmt;
867 
868 		  default:		/* just another character */
869 			c = n;
870 			break;
871 		}
872 	}
873 	/* NOTREACHED */
874 }
875