regexec.c

   1 /* NOTE: this is derived from Henry Spencer's regexp code, and should not
   2  * confused with the original package (see point 3 below).  Thanks, Henry!
   3  */
   4
   5 /* Additional note: this code is very heavily munged from Henry's version
   6  * in places.  In some spots I've traded clarity for efficiency, so don't
   7  * blame Henry for some of the lack of readability.
   8  */
   9
  10 /* $Header: regexec.c,v 3.0 89/10/18 15:22:53 lwall Locked $
  11  *
  12  * $Log:        regexec.c,v $
  13  * Revision 3.0  89/10/18  15:22:53  lwall
  14  * 3.0 baseline
  15  *
  16  */
  17
  18 /*
  19  * regcomp and regexec -- regsub and regerror are not used in perl
  20  *
  21  *      Copyright (c) 1986 by University of Toronto.
  22  *      Written by Henry Spencer.  Not derived from licensed software.
  23  *
  24  *      Permission is granted to anyone to use this software for any
  25  *      purpose on any computer system, and to redistribute it freely,
  26  *      subject to the following restrictions:
  27  *
  28  *      1. The author is not responsible for the consequences of use of
  29  *              this software, no matter how awful, even if they arise
  30  *              from defects in it.
  31  *
  32  *      2. The origin of this software must not be misrepresented, either
  33  *              by explicit claim or by omission.
  34  *
  35  *      3. Altered versions must be plainly marked as such, and must not
  36  *              be misrepresented as being the original software.
  37  *
  38  ****    Alterations to Henry's code are...
  39  ****
  40  ****    Copyright (c) 1989, Larry Wall
  41  ****
  42  ****    You may distribute under the terms of the GNU General Public License
  43  ****    as specified in the README file that comes with the perl 3.0 kit.
  44  *
  45  * Beware that some of this code is subtly aware of the way operator
  46  * precedence is structured in regular expressions.  Serious changes in
  47  * regular-expression syntax might require a total rethink.
  48  */
  49 #include "EXTERN.h"
  50 #include "perl.h"
  51 #include "regcomp.h"
  52
  53 #ifndef STATIC
  54 #define STATIC  static
  55 #endif
  56
  57 #ifdef DEBUGGING
  58 int regnarrate = 0;
  59 #endif
  60
  61 /*
  62  * regexec and friends
  63  */
  64
  65 /*
  66  * Global work variables for regexec().
  67  */
  68 static char *regprecomp;
  69 static char *reginput;          /* String-input pointer. */
  70 static char *regbol;            /* Beginning of input, for ^ check. */
  71 static char *regeol;            /* End of input, for $ check. */
  72 static char **regstartp;        /* Pointer to startp array. */
  73 static char **regendp;          /* Ditto for endp. */
  74 static char *reglastparen;      /* Similarly for lastparen. */
  75 static char *regtill;
  76
  77 static char *regmystartp[10];   /* For remembering backreferences. */
  78 static char *regmyendp[10];
  79
  80 /*
  81  * Forwards.
  82  */
  83 STATIC int regtry();
  84 STATIC int regmatch();
  85 STATIC int regrepeat();
  86
  87 extern int multiline;
  88
  89 /*
  90  - regexec - match a regexp against a string
  91  */
  92 int
  93 regexec(prog, stringarg, strend, strbeg, minend, screamer, safebase)
  94 register regexp *prog;
  95 char *stringarg;
  96 register char *strend;  /* pointer to null at end of string */
  97 char *strbeg;   /* real beginning of string */
  98 int minend;     /* end of match must be at least minend after stringarg */
  99 STR *screamer;
 100 int safebase;   /* no need to remember string in subbase */
 101 {
 102         register char *s;
 103         register int i;
 104         register char *c;
 105         register char *string = stringarg;
 106         register int tmp;
 107         int minlen = 0;         /* must match at least this many chars */
 108         int dontbother = 0;     /* how many characters not to try at end */
 109         int beginning = (string == strbeg);     /* is ^ valid at stringarg? */
 110
 111         /* Be paranoid... */
 112         if (prog == NULL || string == NULL) {
 113                 fatal("NULL regexp parameter");
 114                 return(0);
 115         }
 116
 117         regprecomp = prog->precomp;
 118         /* Check validity of program. */
 119         if (UCHARAT(prog->program) != MAGIC) {
 120                 FAIL("corrupted regexp program");
 121         }
 122
 123         if (prog->do_folding) {
 124                 safebase = FALSE;
 125                 i = strend - string;
 126                 New(1101,c,i+1,char);
 127                 (void)bcopy(string, c, i+1);
 128                 string = c;
 129                 strend = string + i;
 130                 for (s = string; s < strend; s++)
 131                         if (isupper(*s))
 132                                 *s = tolower(*s);
 133         }
 134
 135         /* If there is a "must appear" string, look for it. */
 136         s = string;
 137         if (prog->regmust != Nullstr) {
 138                 if (beginning && screamer) {
 139                         if (screamfirst[prog->regmust->str_rare] >= 0)
 140                                 s = screaminstr(screamer,prog->regmust);
 141                         else
 142                                 s = Nullch;
 143                 }
 144 #ifndef lint
 145                 else
 146                         s = fbminstr((unsigned char*)s, (unsigned char*)strend,
 147                             prog->regmust);
 148 #endif
 149                 if (!s) {
 150                         ++prog->regmust->str_u.str_useful;      /* hooray */
 151                         goto phooey;    /* not present */
 152                 }
 153                 else if (prog->regback >= 0) {
 154                         s -= prog->regback;
 155                         if (s < string)
 156                             s = string;
 157                         minlen = prog->regback + prog->regmust->str_cur;
 158                 }
 159                 else if (--prog->regmust->str_u.str_useful < 0) { /* boo */
 160                         str_free(prog->regmust);
 161                         prog->regmust = Nullstr;        /* disable regmust */
 162                         s = string;
 163                 }
 164                 else {
 165                         s = string;
 166                         minlen = prog->regmust->str_cur;
 167                 }
 168         }
 169
 170         /* Mark beginning of line for ^ . */
 171         if (beginning)
 172                 regbol = string;
 173         else
 174                 regbol = NULL;
 175
 176         /* Mark end of line for $ (and such) */
 177         regeol = strend;
 178
 179         /* see how far we have to get to not match where we matched before */
 180         regtill = string+minend;
 181
 182         /* Simplest case:  anchored match need be tried only once. */
 183         /*  [unless multiline is set] */
 184         if (prog->reganch) {
 185                 if (regtry(prog, string))
 186                         goto got_it;
 187                 else if (multiline) {
 188                         if (minlen)
 189                             dontbother = minlen - 1;
 190                         strend -= dontbother;
 191                         /* for multiline we only have to try after newlines */
 192                         if (s > string)
 193                             s--;
 194                         for (; s < strend; s++) {
 195                             if (*s == '\n') {
 196                                 if (++s < strend && regtry(prog, s))
 197                                     goto got_it;
 198                             }
 199                         }
 200                 }
 201                 goto phooey;
 202         }
 203
 204         /* Messy cases:  unanchored match. */
 205         if (prog->regstart) {
 206                 /* We know what string it must start with. */
 207                 if (prog->regstart->str_pok == 3) {
 208 #ifndef lint
 209                     while ((s = fbminstr((unsigned char*)s,
 210                       (unsigned char*)strend, prog->regstart)) != NULL)
 211 #else
 212                     while (s = Nullch)
 213 #endif
 214                     {
 215                             if (regtry(prog, s))
 216                                     goto got_it;
 217                             s++;
 218                     }
 219                 }
 220                 else {
 221                     c = prog->regstart->str_ptr;
 222                     while ((s = ninstr(s, strend,
 223                       c, c + prog->regstart->str_cur )) != NULL) {
 224                             if (regtry(prog, s))
 225                                     goto got_it;
 226                             s++;
 227                     }
 228                 }
 229                 goto phooey;
 230         }
 231         if (c = prog->regstclass) {
 232                 if (minlen)
 233                     dontbother = minlen - 1;
 234                 strend -= dontbother;   /* don't bother with what can't match */
 235                 /* We know what class it must start with. */
 236                 switch (OP(c)) {
 237                 case ANYOF: case ANYBUT:
 238                     c = OPERAND(c);
 239                     while (s < strend) {
 240                             i = *s;
 241                             if (!(c[i >> 3] & (1 << (i&7))))
 242                                     if (regtry(prog, s))
 243                                             goto got_it;
 244                             s++;
 245                     }
 246                     break;
 247                 case BOUND:
 248                     if (minlen)
 249                         dontbother++,strend--;
 250                     if (s != string) {
 251                         i = s[-1];
 252                         tmp = (isalpha(i) || isdigit(i) || i == '_');
 253                     }
 254                     else
 255                         tmp = 0;        /* assume not alphanumeric */
 256                     while (s < strend) {
 257                             i = *s;
 258                             if (tmp != (isalpha(i) || isdigit(i) || i == '_')) {
 259                                     tmp = !tmp;
 260                                     if (regtry(prog, s))
 261                                             goto got_it;
 262                             }
 263                             s++;
 264                     }
 265                     if (tmp && regtry(prog,s))
 266                             goto got_it;
 267                     break;
 268                 case NBOUND:
 269                     if (minlen)
 270                         dontbother++,strend--;
 271                     if (s != string) {
 272                         i = s[-1];
 273                         tmp = (isalpha(i) || isdigit(i) || i == '_');
 274                     }
 275                     else
 276                         tmp = 0;        /* assume not alphanumeric */
 277                     while (s < strend) {
 278                             i = *s;
 279                             if (tmp != (isalpha(i) || isdigit(i) || i == '_'))
 280                                     tmp = !tmp;
 281                             else if (regtry(prog, s))
 282                                     goto got_it;
 283                             s++;
 284                     }
 285                     if (!tmp && regtry(prog,s))
 286                             goto got_it;
 287                     break;
 288                 case ALNUM:
 289                     while (s < strend) {
 290                             i = *s;
 291                             if (isalpha(i) || isdigit(i) || i == '_')
 292                                     if (regtry(prog, s))
 293                                             goto got_it;
 294                             s++;
 295                     }
 296                     break;
 297                 case NALNUM:
 298                     while (s < strend) {
 299                             i = *s;
 300                             if (!isalpha(i) && !isdigit(i) && i != '_')
 301                                     if (regtry(prog, s))
 302                                             goto got_it;
 303                             s++;
 304                     }
 305                     break;
 306                 case SPACE:
 307                     while (s < strend) {
 308                             if (isspace(*s))
 309                                     if (regtry(prog, s))
 310                                             goto got_it;
 311                             s++;
 312                     }
 313                     break;
 314                 case NSPACE:
 315                     while (s < strend) {
 316                             if (!isspace(*s))
 317                                     if (regtry(prog, s))
 318                                             goto got_it;
 319                             s++;
 320                     }
 321                     break;
 322                 case DIGIT:
 323                     while (s < strend) {
 324                             if (isdigit(*s))
 325                                     if (regtry(prog, s))
 326                                             goto got_it;
 327                             s++;
 328                     }
 329                     break;
 330                 case NDIGIT:
 331                     while (s < strend) {
 332                             if (!isdigit(*s))
 333                                     if (regtry(prog, s))
 334                                             goto got_it;
 335                             s++;
 336                     }
 337                     break;
 338                 }
 339         }
 340         else {
 341                 dontbother = minend;
 342                 strend -= dontbother;
 343                 /* We don't know much -- general case. */
 344                 do {
 345                         if (regtry(prog, s))
 346                                 goto got_it;
 347                 } while (s++ < strend);
 348         }
 349
 350         /* Failure. */
 351         goto phooey;
 352
 353     got_it:
 354         if ((!safebase && (prog->nparens || sawampersand)) || prog->do_folding){
 355                 strend += dontbother;   /* uncheat */
 356                 if (safebase)                   /* no need for $digit later */
 357                     s = strbeg;
 358                 else if (strbeg != prog->subbase) {
 359                     i = strend - string + (stringarg - strbeg);
 360                     s = nsavestr(strbeg,i);     /* so $digit will work later */
 361                     if (prog->subbase)
 362                             Safefree(prog->subbase);
 363                     prog->subbase = s;
 364                 }
 365                 else
 366                     s = prog->subbase;
 367                 s += (stringarg - strbeg);
 368                 for (i = 0; i <= prog->nparens; i++) {
 369                         if (prog->endp[i]) {
 370                             prog->startp[i] = s + (prog->startp[i] - string);
 371                             prog->endp[i] = s + (prog->endp[i] - string);
 372                         }
 373                 }
 374                 if (prog->do_folding)
 375                         Safefree(string);
 376         }
 377         return(1);
 378
 379     phooey:
 380         if (prog->do_folding)
 381                 Safefree(string);
 382         return(0);
 383 }
 384
 385 /*
 386  - regtry - try match at specific point
 387  */
 388 static int                      /* 0 failure, 1 success */
 389 regtry(prog, string)
 390 regexp *prog;
 391 char *string;
 392 {
 393         register int i;
 394         register char **sp;
 395         register char **ep;
 396
 397         reginput = string;
 398         regstartp = prog->startp;
 399         regendp = prog->endp;
 400         reglastparen = &prog->lastparen;
 401         prog->lastparen = 0;
 402
 403         sp = prog->startp;
 404         ep = prog->endp;
 405         if (prog->nparens) {
 406                 for (i = NSUBEXP; i > 0; i--) {
 407                         *sp++ = NULL;
 408                         *ep++ = NULL;
 409                 }
 410         }
 411         if (regmatch(prog->program + 1) && reginput >= regtill) {
 412                 prog->startp[0] = string;
 413                 prog->endp[0] = reginput;
 414                 return(1);
 415         } else
 416                 return(0);
 417 }
 418
 419 /*
 420  - regmatch - main matching routine
 421  *
 422  * Conceptually the strategy is simple:  check to see whether the current
 423  * node matches, call self recursively to see whether the rest matches,
 424  * and then act accordingly.  In practice we make some effort to avoid
 425  * recursion, in particular by going through "ordinary" nodes (that don't
 426  * need to know whether the rest of the match failed) by a loop instead of
 427  * by recursion.
 428  */
 429 /* [lwall] I've hoisted the register declarations to the outer block in order to
 430  * maybe save a little bit of pushing and popping on the stack.  It also takes
 431  * advantage of machines that use a register save mask on subroutine entry.
 432  */
 433 static int                      /* 0 failure, 1 success */
 434 regmatch(prog)
 435 char *prog;
 436 {
 437         register char *scan;    /* Current node. */
 438         char *next;             /* Next node. */
 439         register int nextchar;
 440         register int n;         /* no or next */
 441         register int ln;        /* len or last */
 442         register char *s;       /* operand or save */
 443         register char *locinput = reginput;
 444
 445         nextchar = *locinput;
 446         scan = prog;
 447 #ifdef DEBUGGING
 448         if (scan != NULL && regnarrate)
 449                 fprintf(stderr, "%s(\n", regprop(scan));
 450 #endif
 451         while (scan != NULL) {
 452 #ifdef DEBUGGING
 453                 if (regnarrate)
 454                         fprintf(stderr, "%s...\n", regprop(scan));
 455 #endif
 456
 457 #ifdef REGALIGN
 458                 next = scan + NEXT(scan);
 459                 if (next == scan)
 460                     next = NULL;
 461 #else
 462                 next = regnext(scan);
 463 #endif
 464
 465                 switch (OP(scan)) {
 466                 case BOL:
 467                         if (locinput == regbol ||
 468                             ((nextchar || locinput < regeol) &&
 469                               locinput[-1] == '\n') )
 470                         {
 471                                 regtill--;
 472                                 break;
 473                         }
 474                         return(0);
 475                 case EOL:
 476                         if ((nextchar || locinput < regeol) && nextchar != '\n')
 477                                 return(0);
 478                         regtill--;
 479                         break;
 480                 case ANY:
 481                         if ((nextchar == '\0' && locinput >= regeol) ||
 482                           nextchar == '\n')
 483                                 return(0);
 484                         nextchar = *++locinput;
 485                         break;
 486                 case EXACTLY:
 487                         s = OPERAND(scan);
 488                         ln = *s++;
 489                         /* Inline the first character, for speed. */
 490                         if (*s != nextchar)
 491                                 return(0);
 492                         if (locinput + ln > regeol)
 493                                 return 0;
 494                         if (ln > 1 && bcmp(s, locinput, ln) != 0)
 495                                 return(0);
 496                         locinput += ln;
 497                         nextchar = *locinput;
 498                         break;
 499                 case ANYOF:
 500                 case ANYBUT:
 501                         s = OPERAND(scan);
 502                         if (nextchar < 0)
 503                                 nextchar = UCHARAT(locinput);
 504                         if (s[nextchar >> 3] & (1 << (nextchar&7)))
 505                                 return(0);
 506                         nextchar = *++locinput;
 507                         if (!nextchar && locinput > regeol)
 508                                 return 0;
 509                         break;
 510                 case ALNUM:
 511                         if (!nextchar)
 512                                 return(0);
 513                         if (!isalpha(nextchar) && !isdigit(nextchar) &&
 514                           nextchar != '_')
 515                                 return(0);
 516                         nextchar = *++locinput;
 517                         break;
 518                 case NALNUM:
 519                         if (!nextchar && locinput >= regeol)
 520                                 return(0);
 521                         if (isalpha(nextchar) || isdigit(nextchar) ||
 522                           nextchar == '_')
 523                                 return(0);
 524                         nextchar = *++locinput;
 525                         break;
 526                 case NBOUND:
 527                 case BOUND:
 528                         if (locinput == regbol) /* was last char in word? */
 529                                 ln = 0;
 530                         else
 531                                 ln = (isalpha(locinput[-1]) ||
 532                                      isdigit(locinput[-1]) ||
 533                                      locinput[-1] == '_' );
 534                         n = (isalpha(nextchar) || isdigit(nextchar) ||
 535                             nextchar == '_' );  /* is next char in word? */
 536                         if ((ln == n) == (OP(scan) == BOUND))
 537                                 return(0);
 538                         break;
 539                 case SPACE:
 540                         if (!nextchar && locinput >= regeol)
 541                                 return(0);
 542                         if (!isspace(nextchar))
 543                                 return(0);
 544                         nextchar = *++locinput;
 545                         break;
 546                 case NSPACE:
 547                         if (!nextchar)
 548                                 return(0);
 549                         if (isspace(nextchar))
 550                                 return(0);
 551                         nextchar = *++locinput;
 552                         break;
 553                 case DIGIT:
 554                         if (!isdigit(nextchar))
 555                                 return(0);
 556                         nextchar = *++locinput;
 557                         break;
 558                 case NDIGIT:
 559                         if (!nextchar && locinput >= regeol)
 560                                 return(0);
 561                         if (isdigit(nextchar))
 562                                 return(0);
 563                         nextchar = *++locinput;
 564                         break;
 565                 case REF:
 566                 case REF+1:
 567                 case REF+2:
 568                 case REF+3:
 569                 case REF+4:
 570                 case REF+5:
 571                 case REF+6:
 572                 case REF+7:
 573                 case REF+8:
 574                 case REF+9:
 575                         n = OP(scan) - REF;
 576                         s = regmystartp[n];
 577                         if (!s)
 578                             return(0);
 579                         if (!regmyendp[n])
 580                             return(0);
 581                         if (s == regmyendp[n])
 582                             break;
 583                         /* Inline the first character, for speed. */
 584                         if (*s != nextchar)
 585                                 return(0);
 586                         ln = regmyendp[n] - s;
 587                         if (locinput + ln > regeol)
 588                                 return 0;
 589                         if (ln > 1 && bcmp(s, locinput, ln) != 0)
 590                                 return(0);
 591                         locinput += ln;
 592                         nextchar = *locinput;
 593                         break;
 594
 595                 case NOTHING:
 596                         break;
 597                 case BACK:
 598                         break;
 599                 case OPEN+1:
 600                 case OPEN+2:
 601                 case OPEN+3:
 602                 case OPEN+4:
 603                 case OPEN+5:
 604                 case OPEN+6:
 605                 case OPEN+7:
 606                 case OPEN+8:
 607                 case OPEN+9:
 608                         n = OP(scan) - OPEN;
 609                         reginput = locinput;
 610
 611                         regmystartp[n] = locinput;      /* for REF */
 612                         if (regmatch(next)) {
 613                                 /*
 614                                  * Don't set startp if some later
 615                                  * invocation of the same parentheses
 616                                  * already has.
 617                                  */
 618                                 if (regstartp[n] == NULL)
 619                                         regstartp[n] = locinput;
 620                                 return(1);
 621                         } else
 622                                 return(0);
 623                         /* NOTREACHED */
 624                 case CLOSE+1:
 625                 case CLOSE+2:
 626                 case CLOSE+3:
 627                 case CLOSE+4:
 628                 case CLOSE+5:
 629                 case CLOSE+6:
 630                 case CLOSE+7:
 631                 case CLOSE+8:
 632                 case CLOSE+9: {
 633                                 n = OP(scan) - CLOSE;
 634                                 reginput = locinput;
 635
 636                                 regmyendp[n] = locinput;        /* for REF */
 637                                 if (regmatch(next)) {
 638                                         /*
 639                                          * Don't set endp if some later
 640                                          * invocation of the same parentheses
 641                                          * already has.
 642                                          */
 643                                         if (regendp[n] == NULL) {
 644                                                 regendp[n] = locinput;
 645                                                 if (n > *reglastparen)
 646                                                     *reglastparen = n;
 647                                         }
 648                                         return(1);
 649                                 } else
 650                                         return(0);
 651                         }
 652                         /*NOTREACHED*/
 653                 case BRANCH: {
 654                                 if (OP(next) != BRANCH)         /* No choice. */
 655                                         next = NEXTOPER(scan);  /* Avoid recursion. */
 656                                 else {
 657                                         do {
 658                                                 reginput = locinput;
 659                                                 if (regmatch(NEXTOPER(scan)))
 660                                                         return(1);
 661 #ifdef REGALIGN
 662                                                 if (n = NEXT(scan))
 663                                                     scan += n;
 664                                                 else
 665                                                     scan = NULL;
 666 #else
 667                                                 scan = regnext(scan);
 668 #endif
 669                                         } while (scan != NULL && OP(scan) == BRANCH);
 670                                         return(0);
 671                                         /* NOTREACHED */
 672                                 }
 673                         }
 674                         break;
 675                 case STAR:
 676                 case PLUS:
 677                         /*
 678                          * Lookahead to avoid useless match attempts
 679                          * when we know what character comes next.
 680                          */
 681                         if (OP(next) == EXACTLY)
 682                                 nextchar = *(OPERAND(next)+1);
 683                         else
 684                                 nextchar = -1000;
 685                         ln = (OP(scan) == STAR) ? 0 : 1;
 686                         reginput = locinput;
 687                         n = regrepeat(NEXTOPER(scan));
 688                         while (n >= ln) {
 689                                 /* If it could work, try it. */
 690                                 if (nextchar == -1000 || *reginput == nextchar)
 691                                         if (regmatch(next))
 692                                                 return(1);
 693                                 /* Couldn't or didn't -- back up. */
 694                                 n--;
 695                                 reginput = locinput + n;
 696                         }
 697                         return(0);
 698                 case END:
 699                         reginput = locinput; /* put where regtry can find it */
 700                         return(1);      /* Success! */
 701                 default:
 702                         printf("%x %d\n",scan,scan[1]);
 703                         FAIL("regexp memory corruption");
 704                 }
 705
 706                 scan = next;
 707         }
 708
 709         /*
 710          * We get here only if there's trouble -- normally "case END" is
 711          * the terminating point.
 712          */
 713         FAIL("corrupted regexp pointers");
 714         /*NOTREACHED*/
 715 #ifdef lint
 716         return 0;
 717 #endif
 718 }
 719
 720 /*
 721  - regrepeat - repeatedly match something simple, report how many
 722  */
 723 /*
 724  * [This routine now assumes that it will only match on things of length 1.
 725  * That was true before, but now we assume scan - reginput is the count,
 726  * rather than incrementing count on every character.]
 727  */
 728 static int
 729 regrepeat(p)
 730 char *p;
 731 {
 732         register char *scan;
 733         register char *opnd;
 734         register int c;
 735         register char *loceol = regeol;
 736
 737         scan = reginput;
 738         opnd = OPERAND(p);
 739         switch (OP(p)) {
 740         case ANY:
 741                 while (scan < loceol && *scan != '\n')
 742                         scan++;
 743                 break;
 744         case EXACTLY:           /* length of string is 1 */
 745                 opnd++;
 746                 while (scan < loceol && *opnd == *scan)
 747                         scan++;
 748                 break;
 749         case ANYOF:
 750         case ANYBUT:
 751                 c = UCHARAT(scan);
 752                 while (scan < loceol && !(opnd[c >> 3] & (1 << (c & 7)))) {
 753                         scan++;
 754                         c = UCHARAT(scan);
 755                 }
 756                 break;
 757         case ALNUM:
 758                 while (isalpha(*scan) || isdigit(*scan) || *scan == '_')
 759                         scan++;
 760                 break;
 761         case NALNUM:
 762                 while (scan < loceol && (!isalpha(*scan) && !isdigit(*scan) &&
 763                   *scan != '_'))
 764                         scan++;
 765                 break;
 766         case SPACE:
 767                 while (scan < loceol && isspace(*scan))
 768                         scan++;
 769                 break;
 770         case NSPACE:
 771                 while (scan < loceol && !isspace(*scan))
 772                         scan++;
 773                 break;
 774         case DIGIT:
 775                 while (isdigit(*scan))
 776                         scan++;
 777                 break;
 778         case NDIGIT:
 779                 while (scan < loceol && !isdigit(*scan))
 780                         scan++;
 781                 break;
 782         default:                /* Oh dear.  Called inappropriately. */
 783                 FAIL("internal regexp foulup");
 784                 /* NOTREACHED */
 785         }
 786
 787         c = scan - reginput;
 788         reginput = scan;
 789
 790         return(c);
 791 }
 792
 793 /*
 794  - regnext - dig the "next" pointer out of a node
 795  *
 796  * [Note, when REGALIGN is defined there are two places in regmatch()
 797  * that bypass this code for speed.]
 798  */
 799 char *
 800 regnext(p)
 801 register char *p;
 802 {
 803         register int offset;
 804
 805         if (p == &regdummy)
 806                 return(NULL);
 807
 808         offset = NEXT(p);
 809         if (offset == 0)
 810                 return(NULL);
 811
 812 #ifdef REGALIGN
 813         return(p+offset);
 814 #else
 815         if (OP(p) == BACK)
 816                 return(p-offset);
 817         else
 818                 return(p+offset);
 819 #endif
 820 }