contrib/less/regexp.c

   1 /*
   2  * regcomp and regexec -- regsub and regerror are elsewhere
   3  *
   4  *      Copyright (c) 1986 by University of Toronto.
   5  *      Written by Henry Spencer.  Not derived from licensed software.
   6  *
   7  *      Permission is granted to anyone to use this software for any
   8  *      purpose on any computer system, and to redistribute it freely,
   9  *      subject to the following restrictions:
  10  *
  11  *      1. The author is not responsible for the consequences of use of
  12  *              this software, no matter how awful, even if they arise
  13  *              from defects in it.
  14  *
  15  *      2. The origin of this software must not be misrepresented, either
  16  *              by explicit claim or by omission.
  17  *
  18  *      3. Altered versions must be plainly marked as such, and must not
  19  *              be misrepresented as being the original software.
  20  *
  21  * Beware that some of this code is subtly aware of the way operator
  22  * precedence is structured in regular expressions.  Serious changes in
  23  * regular-expression syntax might require a total rethink.
  24  *
  25  * *** NOTE: this code has been altered slightly for use in Tcl. ***
  26  * Slightly modified by David MacKenzie to undo most of the changes for TCL.
  27  * Added regexec2 with notbol parameter. -- 4/19/99 Mark Nudelman
  28  */
  29
  30 #include "less.h"
  31 #if HAVE_STDIO_H
  32 #include <stdio.h>
  33 #endif
  34 #if HAVE_STDLIB_H
  35 #include <stdlib.h>
  36 #endif
  37 #if HAVE_STRING_H
  38 #include <string.h>
  39 #endif
  40 #include "regexp.h"
  41
  42 /*
  43  * The "internal use only" fields in regexp.h are present to pass info from
  44  * compile to execute that permits the execute phase to run lots faster on
  45  * simple cases.  They are:
  46  *
  47  * regstart     char that must begin a match; '\0' if none obvious
  48  * reganch      is the match anchored (at beginning-of-line only)?
  49  * regmust      string (pointer into program) that match must include, or NULL
  50  * regmlen      length of regmust string
  51  *
  52  * Regstart and reganch permit very fast decisions on suitable starting points
  53  * for a match, cutting down the work a lot.  Regmust permits fast rejection
  54  * of lines that cannot possibly match.  The regmust tests are costly enough
  55  * that regcomp() supplies a regmust only if the r.e. contains something
  56  * potentially expensive (at present, the only such thing detected is * or +
  57  * at the start of the r.e., which can involve a lot of backup).  Regmlen is
  58  * supplied because the test in regexec() needs it and regcomp() is
  59  * computing it anyway.
  60  */
  61
  62 /*
  63  * Structure for regexp "program".  This is essentially a linear encoding
  64  * of a nondeterministic finite-state machine (aka syntax charts or
  65  * "railroad normal form" in parsing technology).  Each node is an opcode
  66  * plus a "next" pointer, possibly plus an operand.  "Next" pointers of
  67  * all nodes except BRANCH implement concatenation; a "next" pointer with
  68  * a BRANCH on both ends of it is connecting two alternatives.  (Here we
  69  * have one of the subtle syntax dependencies:  an individual BRANCH (as
  70  * opposed to a collection of them) is never concatenated with anything
  71  * because of operator precedence.)  The operand of some types of node is
  72  * a literal string; for others, it is a node leading into a sub-FSM.  In
  73  * particular, the operand of a BRANCH node is the first node of the branch.
  74  * (NB this is *not* a tree structure:  the tail of the branch connects
  75  * to the thing following the set of BRANCHes.)  The opcodes are:
  76  */
  77
  78 /* definition   number  opnd?   meaning */
  79 #undef EOL
  80 #define END     0       /* no   End of program. */
  81 #define BOL     1       /* no   Match "" at beginning of line. */
  82 #define EOL     2       /* no   Match "" at end of line. */
  83 #define ANY     3       /* no   Match any one character. */
  84 #define ANYOF   4       /* str  Match any character in this string. */
  85 #define ANYBUT  5       /* str  Match any character not in this string. */
  86 #define BRANCH  6       /* node Match this alternative, or the next... */
  87 #define BACK    7       /* no   Match "", "next" ptr points backward. */
  88 #define EXACTLY 8       /* str  Match this string. */
  89 #define NOTHING 9       /* no   Match empty string. */
  90 #define STAR    10      /* node Match this (simple) thing 0 or more times. */
  91 #define PLUS    11      /* node Match this (simple) thing 1 or more times. */
  92 #define OPEN    20      /* no   Mark this point in input as start of #n. */
  93                         /*      OPEN+1 is number 1, etc. */
  94 #define CLOSE   30      /* no   Analogous to OPEN. */
  95
  96 /*
  97  * Opcode notes:
  98  *
  99  * BRANCH       The set of branches constituting a single choice are hooked
 100  *              together with their "next" pointers, since precedence prevents
 101  *              anything being concatenated to any individual branch.  The
 102  *              "next" pointer of the last BRANCH in a choice points to the
 103  *              thing following the whole choice.  This is also where the
 104  *              final "next" pointer of each individual branch points; each
 105  *              branch starts with the operand node of a BRANCH node.
 106  *
 107  * BACK         Normal "next" pointers all implicitly point forward; BACK
 108  *              exists to make loop structures possible.
 109  *
 110  * STAR,PLUS    '?', and complex '*' and '+', are implemented as circular
 111  *              BRANCH structures using BACK.  Simple cases (one character
 112  *              per match) are implemented with STAR and PLUS for speed
 113  *              and to minimize recursive plunges.
 114  *
 115  * OPEN,CLOSE   ...are numbered at compile time.
 116  */
 117
 118 /*
 119  * A node is one char of opcode followed by two chars of "next" pointer.
 120  * "Next" pointers are stored as two 8-bit pieces, high order first.  The
 121  * value is a positive offset from the opcode of the node containing it.
 122  * An operand, if any, simply follows the node.  (Note that much of the
 123  * code generation knows about this implicit relationship.)
 124  *
 125  * Using two bytes for the "next" pointer is vast overkill for most things,
 126  * but allows patterns to get big without disasters.
 127  */
 128 #define OP(p)   (*(p))
 129 #define NEXT(p) (((*((p)+1)&0377)<<8) + (*((p)+2)&0377))
 130 #define OPERAND(p)      ((p) + 3)
 131
 132 /*
 133  * See regmagic.h for one further detail of program structure.
 134  */
 135
 136
 137 /*
 138  * Utility definitions.
 139  */
 140 #ifndef CHARBITS
 141 #define UCHARAT(p)      ((int)*(unsigned char *)(p))
 142 #else
 143 #define UCHARAT(p)      ((int)*(p)&CHARBITS)
 144 #endif
 145
 146 #define FAIL(m) { regerror(m); return(NULL); }
 147 #define ISMULT(c)       ((c) == '*' || (c) == '+' || (c) == '?')
 148 #define META    "^$.[()|?+*\\"
 149
 150 /*
 151  * Flags to be passed up and down.
 152  */
 153 #define HASWIDTH        01      /* Known never to match null string. */
 154 #define SIMPLE          02      /* Simple enough to be STAR/PLUS operand. */
 155 #define SPSTART         04      /* Starts with * or +. */
 156 #define WORST           0       /* Worst case. */
 157
 158 /*
 159  * Global work variables for regcomp().
 160  */
 161 static char *regparse;          /* Input-scan pointer. */
 162 static int regnpar;             /* () count. */
 163 static char regdummy;
 164 static char *regcode;           /* Code-emit pointer; &regdummy = don't. */
 165 static long regsize;            /* Code size. */
 166
 167 /*
 168  * The first byte of the regexp internal "program" is actually this magic
 169  * number; the start node begins in the second byte.
 170  */
 171 #define MAGIC   0234
 172
 173
 174 /*
 175  * Forward declarations for regcomp()'s friends.
 176  */
 177 #ifndef STATIC
 178 #define STATIC  static
 179 #endif
 180 STATIC char *reg();
 181 STATIC char *regbranch();
 182 STATIC char *regpiece();
 183 STATIC char *regatom();
 184 STATIC char *regnode();
 185 STATIC char *regnext();
 186 STATIC void regc();
 187 STATIC void reginsert();
 188 STATIC void regtail();
 189 STATIC void regoptail();
 190 #ifdef STRCSPN
 191 STATIC int strcspn();
 192 #endif
 193
 194 /*
 195  - regcomp - compile a regular expression into internal code
 196  *
 197  * We can't allocate space until we know how big the compiled form will be,
 198  * but we can't compile it (and thus know how big it is) until we've got a
 199  * place to put the code.  So we cheat:  we compile it twice, once with code
 200  * generation turned off and size counting turned on, and once "for real".
 201  * This also means that we don't allocate space until we are sure that the
 202  * thing really will compile successfully, and we never have to move the
 203  * code and thus invalidate pointers into it.  (Note that it has to be in
 204  * one piece because free() must be able to free it all.)
 205  *
 206  * Beware that the optimization-preparation code in here knows about some
 207  * of the structure of the compiled regexp.
 208  */
 209 regexp *
 210 regcomp(exp)
 211 char *exp;
 212 {
 213         register regexp *r;
 214         register char *scan;
 215         register char *longest;
 216         register int len;
 217         int flags;
 218
 219         if (exp == NULL)
 220                 FAIL("NULL argument");
 221
 222         /* First pass: determine size, legality. */
 223         regparse = exp;
 224         regnpar = 1;
 225         regsize = 0L;
 226         regcode = &regdummy;
 227         regc(MAGIC);
 228         if (reg(0, &flags) == NULL)
 229                 return(NULL);
 230
 231         /* Small enough for pointer-storage convention? */
 232         if (regsize >= 32767L)          /* Probably could be 65535L. */
 233                 FAIL("regexp too big");
 234
 235         /* Allocate space. */
 236         r = (regexp *)malloc(sizeof(regexp) + (unsigned)regsize);
 237         if (r == NULL)
 238                 FAIL("out of space");
 239
 240         /* Second pass: emit code. */
 241         regparse = exp;
 242         regnpar = 1;
 243         regcode = r->program;
 244         regc(MAGIC);
 245         if (reg(0, &flags) == NULL)
 246                 return(NULL);
 247
 248         /* Dig out information for optimizations. */
 249         r->regstart = '\0';     /* Worst-case defaults. */
 250         r->reganch = 0;
 251         r->regmust = NULL;
 252         r->regmlen = 0;
 253         scan = r->program+1;                    /* First BRANCH. */
 254         if (OP(regnext(scan)) == END) {         /* Only one top-level choice. */
 255                 scan = OPERAND(scan);
 256
 257                 /* Starting-point info. */
 258                 if (OP(scan) == EXACTLY)
 259                         r->regstart = *OPERAND(scan);
 260                 else if (OP(scan) == BOL)
 261                         r->reganch++;
 262
 263                 /*
 264                  * If there's something expensive in the r.e., find the
 265                  * longest literal string that must appear and make it the
 266                  * regmust.  Resolve ties in favor of later strings, since
 267                  * the regstart check works with the beginning of the r.e.
 268                  * and avoiding duplication strengthens checking.  Not a
 269                  * strong reason, but sufficient in the absence of others.
 270                  */
 271                 if (flags&SPSTART) {
 272                         longest = NULL;
 273                         len = 0;
 274                         for (; scan != NULL; scan = regnext(scan))
 275                                 if (OP(scan) == EXACTLY && ((int) strlen(OPERAND(scan))) >= len) {
 276                                         longest = OPERAND(scan);
 277                                         len = strlen(OPERAND(scan));
 278                                 }
 279                         r->regmust = longest;
 280                         r->regmlen = len;
 281                 }
 282         }
 283
 284         return(r);
 285 }
 286
 287 /*
 288  - reg - regular expression, i.e. main body or parenthesized thing
 289  *
 290  * Caller must absorb opening parenthesis.
 291  *
 292  * Combining parenthesis handling with the base level of regular expression
 293  * is a trifle forced, but the need to tie the tails of the branches to what
 294  * follows makes it hard to avoid.
 295  */
 296 static char *
 297 reg(paren, flagp)
 298 int paren;                      /* Parenthesized? */
 299 int *flagp;
 300 {
 301         register char *ret;
 302         register char *br;
 303         register char *ender;
 304         register int parno = 0;
 305         int flags;
 306
 307         *flagp = HASWIDTH;      /* Tentatively. */
 308
 309         /* Make an OPEN node, if parenthesized. */
 310         if (paren) {
 311                 if (regnpar >= NSUBEXP)
 312                         FAIL("too many ()");
 313                 parno = regnpar;
 314                 regnpar++;
 315                 ret = regnode(OPEN+parno);
 316         } else
 317                 ret = NULL;
 318
 319         /* Pick up the branches, linking them together. */
 320         br = regbranch(&flags);
 321         if (br == NULL)
 322                 return(NULL);
 323         if (ret != NULL)
 324                 regtail(ret, br);       /* OPEN -> first. */
 325         else
 326                 ret = br;
 327         if (!(flags&HASWIDTH))
 328                 *flagp &= ~HASWIDTH;
 329         *flagp |= flags&SPSTART;
 330         while (*regparse == '|') {
 331                 regparse++;
 332                 br = regbranch(&flags);
 333                 if (br == NULL)
 334                         return(NULL);
 335                 regtail(ret, br);       /* BRANCH -> BRANCH. */
 336                 if (!(flags&HASWIDTH))
 337                         *flagp &= ~HASWIDTH;
 338                 *flagp |= flags&SPSTART;
 339         }
 340
 341         /* Make a closing node, and hook it on the end. */
 342         ender = regnode((paren) ? CLOSE+parno : END);
 343         regtail(ret, ender);
 344
 345         /* Hook the tails of the branches to the closing node. */
 346         for (br = ret; br != NULL; br = regnext(br))
 347                 regoptail(br, ender);
 348
 349         /* Check for proper termination. */
 350         if (paren && *regparse++ != ')') {
 351                 FAIL("unmatched ()");
 352         } else if (!paren && *regparse != '\0') {
 353                 if (*regparse == ')') {
 354                         FAIL("unmatched ()");
 355                 } else
 356                         FAIL("junk on end");    /* "Can't happen". */
 357                 /* NOTREACHED */
 358         }
 359
 360         return(ret);
 361 }
 362
 363 /*
 364  - regbranch - one alternative of an | operator
 365  *
 366  * Implements the concatenation operator.
 367  */
 368 static char *
 369 regbranch(flagp)
 370 int *flagp;
 371 {
 372         register char *ret;
 373         register char *chain;
 374         register char *latest;
 375         int flags;
 376
 377         *flagp = WORST;         /* Tentatively. */
 378
 379         ret = regnode(BRANCH);
 380         chain = NULL;
 381         while (*regparse != '\0' && *regparse != '|' && *regparse != ')') {
 382                 latest = regpiece(&flags);
 383                 if (latest == NULL)
 384                         return(NULL);
 385                 *flagp |= flags&HASWIDTH;
 386                 if (chain == NULL)      /* First piece. */
 387                         *flagp |= flags&SPSTART;
 388                 else
 389                         regtail(chain, latest);
 390                 chain = latest;
 391         }
 392         if (chain == NULL)      /* Loop ran zero times. */
 393                 (void) regnode(NOTHING);
 394
 395         return(ret);
 396 }
 397
 398 /*
 399  - regpiece - something followed by possible [*+?]
 400  *
 401  * Note that the branching code sequences used for ? and the general cases
 402  * of * and + are somewhat optimized:  they use the same NOTHING node as
 403  * both the endmarker for their branch list and the body of the last branch.
 404  * It might seem that this node could be dispensed with entirely, but the
 405  * endmarker role is not redundant.
 406  */
 407 static char *
 408 regpiece(flagp)
 409 int *flagp;
 410 {
 411         register char *ret;
 412         register char op;
 413         register char *next;
 414         int flags;
 415
 416         ret = regatom(&flags);
 417         if (ret == NULL)
 418                 return(NULL);
 419
 420         op = *regparse;
 421         if (!ISMULT(op)) {
 422                 *flagp = flags;
 423                 return(ret);
 424         }
 425
 426         if (!(flags&HASWIDTH) && op != '?')
 427                 FAIL("*+ operand could be empty");
 428         *flagp = (op != '+') ? (WORST|SPSTART) : (WORST|HASWIDTH);
 429
 430         if (op == '*' && (flags&SIMPLE))
 431                 reginsert(STAR, ret);
 432         else if (op == '*') {
 433                 /* Emit x* as (x&|), where & means "self". */
 434                 reginsert(BRANCH, ret);                 /* Either x */
 435                 regoptail(ret, regnode(BACK));          /* and loop */
 436                 regoptail(ret, ret);                    /* back */
 437                 regtail(ret, regnode(BRANCH));          /* or */
 438                 regtail(ret, regnode(NOTHING));         /* null. */
 439         } else if (op == '+' && (flags&SIMPLE))
 440                 reginsert(PLUS, ret);
 441         else if (op == '+') {
 442                 /* Emit x+ as x(&|), where & means "self". */
 443                 next = regnode(BRANCH);                 /* Either */
 444                 regtail(ret, next);
 445                 regtail(regnode(BACK), ret);            /* loop back */
 446                 regtail(next, regnode(BRANCH));         /* or */
 447                 regtail(ret, regnode(NOTHING));         /* null. */
 448         } else if (op == '?') {
 449                 /* Emit x? as (x|) */
 450                 reginsert(BRANCH, ret);                 /* Either x */
 451                 regtail(ret, regnode(BRANCH));          /* or */
 452                 next = regnode(NOTHING);                /* null. */
 453                 regtail(ret, next);
 454                 regoptail(ret, next);
 455         }
 456         regparse++;
 457         if (ISMULT(*regparse))
 458                 FAIL("nested *?+");
 459
 460         return(ret);
 461 }
 462
 463 /*
 464  - regatom - the lowest level
 465  *
 466  * Optimization:  gobbles an entire sequence of ordinary characters so that
 467  * it can turn them into a single node, which is smaller to store and
 468  * faster to run.  Backslashed characters are exceptions, each becoming a
 469  * separate node; the code is simpler that way and it's not worth fixing.
 470  */
 471 static char *
 472 regatom(flagp)
 473 int *flagp;
 474 {
 475         register char *ret;
 476         int flags;
 477
 478         *flagp = WORST;         /* Tentatively. */
 479
 480         switch (*regparse++) {
 481         case '^':
 482                 ret = regnode(BOL);
 483                 break;
 484         case '$':
 485                 ret = regnode(EOL);
 486                 break;
 487         case '.':
 488                 ret = regnode(ANY);
 489                 *flagp |= HASWIDTH|SIMPLE;
 490                 break;
 491         case '[': {
 492                         register int clss;
 493                         register int classend;
 494
 495                         if (*regparse == '^') { /* Complement of range. */
 496                                 ret = regnode(ANYBUT);
 497                                 regparse++;
 498                         } else
 499                                 ret = regnode(ANYOF);
 500                         if (*regparse == ']' || *regparse == '-')
 501                                 regc(*regparse++);
 502                         while (*regparse != '\0' && *regparse != ']') {
 503                                 if (*regparse == '-') {
 504                                         regparse++;
 505                                         if (*regparse == ']' || *regparse == '\0')
 506                                                 regc('-');
 507                                         else {
 508                                                 clss = UCHARAT(regparse-2)+1;
 509                                                 classend = UCHARAT(regparse);
 510                                                 if (clss > classend+1)
 511                                                         FAIL("invalid [] range");
 512                                                 for (; clss <= classend; clss++)
 513                                                         regc(clss);
 514                                                 regparse++;
 515                                         }
 516                                 } else
 517                                         regc(*regparse++);
 518                         }
 519                         regc('\0');
 520                         if (*regparse != ']')
 521                                 FAIL("unmatched []");
 522                         regparse++;
 523                         *flagp |= HASWIDTH|SIMPLE;
 524                 }
 525                 break;
 526         case '(':
 527                 ret = reg(1, &flags);
 528                 if (ret == NULL)
 529                         return(NULL);
 530                 *flagp |= flags&(HASWIDTH|SPSTART);
 531                 break;
 532         case '\0':
 533         case '|':
 534         case ')':
 535                 FAIL("internal urp");   /* Supposed to be caught earlier. */
 536                 /* NOTREACHED */
 537                 break;
 538         case '?':
 539         case '+':
 540         case '*':
 541                 FAIL("?+* follows nothing");
 542                 /* NOTREACHED */
 543                 break;
 544         case '\\':
 545                 if (*regparse == '\0')
 546                         FAIL("trailing \\");
 547                 ret = regnode(EXACTLY);
 548                 regc(*regparse++);
 549                 regc('\0');
 550                 *flagp |= HASWIDTH|SIMPLE;
 551                 break;
 552         default: {
 553                         register int len;
 554                         register char ender;
 555
 556                         regparse--;
 557                         len = strcspn(regparse, META);
 558                         if (len <= 0)
 559                                 FAIL("internal disaster");
 560                         ender = *(regparse+len);
 561                         if (len > 1 && ISMULT(ender))
 562                                 len--;          /* Back off clear of ?+* operand. */
 563                         *flagp |= HASWIDTH;
 564                         if (len == 1)
 565                                 *flagp |= SIMPLE;
 566                         ret = regnode(EXACTLY);
 567                         while (len > 0) {
 568                                 regc(*regparse++);
 569                                 len--;
 570                         }
 571                         regc('\0');
 572                 }
 573                 break;
 574         }
 575
 576         return(ret);
 577 }
 578
 579 /*
 580  - regnode - emit a node
 581  */
 582 static char *                   /* Location. */
 583 regnode(op)
 584 char op;
 585 {
 586         register char *ret;
 587         register char *ptr;
 588
 589         ret = regcode;
 590         if (ret == &regdummy) {
 591                 regsize += 3;
 592                 return(ret);
 593         }
 594
 595         ptr = ret;
 596         *ptr++ = op;
 597         *ptr++ = '\0';          /* Null "next" pointer. */
 598         *ptr++ = '\0';
 599         regcode = ptr;
 600
 601         return(ret);
 602 }
 603
 604 /*
 605  - regc - emit (if appropriate) a byte of code
 606  */
 607 static void
 608 regc(b)
 609 char b;
 610 {
 611         if (regcode != &regdummy)
 612                 *regcode++ = b;
 613         else
 614                 regsize++;
 615 }
 616
 617 /*
 618  - reginsert - insert an operator in front of already-emitted operand
 619  *
 620  * Means relocating the operand.
 621  */
 622 static void
 623 reginsert(op, opnd)
 624 char op;
 625 char *opnd;
 626 {
 627         register char *src;
 628         register char *dst;
 629         register char *place;
 630
 631         if (regcode == &regdummy) {
 632                 regsize += 3;
 633                 return;
 634         }
 635
 636         src = regcode;
 637         regcode += 3;
 638         dst = regcode;
 639         while (src > opnd)
 640                 *--dst = *--src;
 641
 642         place = opnd;           /* Op node, where operand used to be. */
 643         *place++ = op;
 644         *place++ = '\0';
 645         *place++ = '\0';
 646 }
 647
 648 /*
 649  - regtail - set the next-pointer at the end of a node chain
 650  */
 651 static void
 652 regtail(p, val)
 653 char *p;
 654 char *val;
 655 {
 656         register char *scan;
 657         register char *temp;
 658         register int offset;
 659
 660         if (p == &regdummy)
 661                 return;
 662
 663         /* Find last node. */
 664         scan = p;
 665         for (;;) {
 666                 temp = regnext(scan);
 667                 if (temp == NULL)
 668                         break;
 669                 scan = temp;
 670         }
 671
 672         if (OP(scan) == BACK)
 673                 offset = scan - val;
 674         else
 675                 offset = val - scan;
 676         *(scan+1) = (offset>>8)&0377;
 677         *(scan+2) = offset&0377;
 678 }
 679
 680 /*
 681  - regoptail - regtail on operand of first argument; nop if operandless
 682  */
 683 static void
 684 regoptail(p, val)
 685 char *p;
 686 char *val;
 687 {
 688         /* "Operandless" and "op != BRANCH" are synonymous in practice. */
 689         if (p == NULL || p == &regdummy || OP(p) != BRANCH)
 690                 return;
 691         regtail(OPERAND(p), val);
 692 }
 693
 694 /*
 695  * regexec and friends
 696  */
 697
 698 /*
 699  * Global work variables for regexec().
 700  */
 701 static char *reginput;          /* String-input pointer. */
 702 static char *regbol;            /* Beginning of input, for ^ check. */
 703 static char **regstartp;        /* Pointer to startp array. */
 704 static char **regendp;          /* Ditto for endp. */
 705
 706 /*
 707  * Forwards.
 708  */
 709 STATIC int regtry();
 710 STATIC int regmatch();
 711 STATIC int regrepeat();
 712
 713 #ifdef DEBUG
 714 int regnarrate = 0;
 715 void regdump();
 716 STATIC char *regprop();
 717 #endif
 718
 719 /*
 720  - regexec - match a regexp against a string
 721  */
 722 int
 723 regexec2(prog, string, notbol)
 724 register regexp *prog;
 725 register char *string;
 726 int notbol;
 727 {
 728         register char *s;
 729
 730         /* Be paranoid... */
 731         if (prog == NULL || string == NULL) {
 732                 regerror("NULL parameter");
 733                 return(0);
 734         }
 735
 736         /* Check validity of program. */
 737         if (UCHARAT(prog->program) != MAGIC) {
 738                 regerror("corrupted program");
 739                 return(0);
 740         }
 741
 742         /* If there is a "must appear" string, look for it. */
 743         if (prog->regmust != NULL) {
 744                 s = string;
 745                 while ((s = strchr(s, prog->regmust[0])) != NULL) {
 746                         if (strncmp(s, prog->regmust, prog->regmlen) == 0)
 747                                 break;  /* Found it. */
 748                         s++;
 749                 }
 750                 if (s == NULL)  /* Not present. */
 751                         return(0);
 752         }
 753
 754         /* Mark beginning of line for ^ . */
 755         if (notbol)
 756                 regbol = NULL;
 757         else
 758                 regbol = string;
 759
 760         /* Simplest case:  anchored match need be tried only once. */
 761         if (prog->reganch)
 762                 return(regtry(prog, string));
 763
 764         /* Messy cases:  unanchored match. */
 765         s = string;
 766         if (prog->regstart != '\0')
 767                 /* We know what char it must start with. */
 768                 while ((s = strchr(s, prog->regstart)) != NULL) {
 769                         if (regtry(prog, s))
 770                                 return(1);
 771                         s++;
 772                 }
 773         else
 774                 /* We don't -- general case. */
 775                 do {
 776                         if (regtry(prog, s))
 777                                 return(1);
 778                 } while (*s++ != '\0');
 779
 780         /* Failure. */
 781         return(0);
 782 }
 783
 784 int
 785 regexec(prog, string)
 786 register regexp *prog;
 787 register char *string;
 788 {
 789         return regexec2(prog, string, 0);
 790 }
 791
 792 /*
 793  - regtry - try match at specific point
 794  */
 795 static int                      /* 0 failure, 1 success */
 796 regtry(prog, string)
 797 regexp *prog;
 798 char *string;
 799 {
 800         register int i;
 801         register char **sp;
 802         register char **ep;
 803
 804         reginput = string;
 805         regstartp = prog->startp;
 806         regendp = prog->endp;
 807
 808         sp = prog->startp;
 809         ep = prog->endp;
 810         for (i = NSUBEXP; i > 0; i--) {
 811                 *sp++ = NULL;
 812                 *ep++ = NULL;
 813         }
 814         if (regmatch(prog->program + 1)) {
 815                 prog->startp[0] = string;
 816                 prog->endp[0] = reginput;
 817                 return(1);
 818         } else
 819                 return(0);
 820 }
 821
 822 /*
 823  - regmatch - main matching routine
 824  *
 825  * Conceptually the strategy is simple:  check to see whether the current
 826  * node matches, call self recursively to see whether the rest matches,
 827  * and then act accordingly.  In practice we make some effort to avoid
 828  * recursion, in particular by going through "ordinary" nodes (that don't
 829  * need to know whether the rest of the match failed) by a loop instead of
 830  * by recursion.
 831  */
 832 static int                      /* 0 failure, 1 success */
 833 regmatch(prog)
 834 char *prog;
 835 {
 836         register char *scan;    /* Current node. */
 837         char *next;             /* Next node. */
 838
 839         scan = prog;
 840 #ifdef DEBUG
 841         if (scan != NULL && regnarrate)
 842                 fprintf(stderr, "%s(\n", regprop(scan));
 843 #endif
 844         while (scan != NULL) {
 845 #ifdef DEBUG
 846                 if (regnarrate)
 847                         fprintf(stderr, "%s...\n", regprop(scan));
 848 #endif
 849                 next = regnext(scan);
 850
 851                 switch (OP(scan)) {
 852                 case BOL:
 853                         if (reginput != regbol)
 854                                 return(0);
 855                         break;
 856                 case EOL:
 857                         if (*reginput != '\0')
 858                                 return(0);
 859                         break;
 860                 case ANY:
 861                         if (*reginput == '\0')
 862                                 return(0);
 863                         reginput++;
 864                         break;
 865                 case EXACTLY: {
 866                                 register int len;
 867                                 register char *opnd;
 868
 869                                 opnd = OPERAND(scan);
 870                                 /* Inline the first character, for speed. */
 871                                 if (*opnd != *reginput)
 872                                         return(0);
 873                                 len = strlen(opnd);
 874                                 if (len > 1 && strncmp(opnd, reginput, len) != 0)
 875                                         return(0);
 876                                 reginput += len;
 877                         }
 878                         break;
 879                 case ANYOF:
 880                         if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) == NULL)
 881                                 return(0);
 882                         reginput++;
 883                         break;
 884                 case ANYBUT:
 885                         if (*reginput == '\0' || strchr(OPERAND(scan), *reginput) != NULL)
 886                                 return(0);
 887                         reginput++;
 888                         break;
 889                 case NOTHING:
 890                         break;
 891                 case BACK:
 892                         break;
 893                 case OPEN+1:
 894                 case OPEN+2:
 895                 case OPEN+3:
 896                 case OPEN+4:
 897                 case OPEN+5:
 898                 case OPEN+6:
 899                 case OPEN+7:
 900                 case OPEN+8:
 901                 case OPEN+9: {
 902                                 register int no;
 903                                 register char *save;
 904
 905                                 no = OP(scan) - OPEN;
 906                                 save = reginput;
 907
 908                                 if (regmatch(next)) {
 909                                         /*
 910                                          * Don't set startp if some later
 911                                          * invocation of the same parentheses
 912                                          * already has.
 913                                          */
 914                                         if (regstartp[no] == NULL)
 915                                                 regstartp[no] = save;
 916                                         return(1);
 917                                 } else
 918                                         return(0);
 919                         }
 920                         /* NOTREACHED */
 921                         break;
 922                 case CLOSE+1:
 923                 case CLOSE+2:
 924                 case CLOSE+3:
 925                 case CLOSE+4:
 926                 case CLOSE+5:
 927                 case CLOSE+6:
 928                 case CLOSE+7:
 929                 case CLOSE+8:
 930                 case CLOSE+9: {
 931                                 register int no;
 932                                 register char *save;
 933
 934                                 no = OP(scan) - CLOSE;
 935                                 save = reginput;
 936
 937                                 if (regmatch(next)) {
 938                                         /*
 939                                          * Don't set endp if some later
 940                                          * invocation of the same parentheses
 941                                          * already has.
 942                                          */
 943                                         if (regendp[no] == NULL)
 944                                                 regendp[no] = save;
 945                                         return(1);
 946                                 } else
 947                                         return(0);
 948                         }
 949                         /* NOTREACHED */
 950                         break;
 951                 case BRANCH: {
 952                                 register char *save;
 953
 954                                 if (OP(next) != BRANCH)         /* No choice. */
 955                                         next = OPERAND(scan);   /* Avoid recursion. */
 956                                 else {
 957                                         do {
 958                                                 save = reginput;
 959                                                 if (regmatch(OPERAND(scan)))
 960                                                         return(1);
 961                                                 reginput = save;
 962                                                 scan = regnext(scan);
 963                                         } while (scan != NULL && OP(scan) == BRANCH);
 964                                         return(0);
 965                                         /* NOTREACHED */
 966                                 }
 967                         }
 968                         /* NOTREACHED */
 969                         break;
 970                 case STAR:
 971                 case PLUS: {
 972                                 register char nextch;
 973                                 register int no;
 974                                 register char *save;
 975                                 register int min;
 976
 977                                 /*
 978                                  * Lookahead to avoid useless match attempts
 979                                  * when we know what character comes next.
 980                                  */
 981                                 nextch = '\0';
 982                                 if (OP(next) == EXACTLY)
 983                                         nextch = *OPERAND(next);
 984                                 min = (OP(scan) == STAR) ? 0 : 1;
 985                                 save = reginput;
 986                                 no = regrepeat(OPERAND(scan));
 987                                 while (no >= min) {
 988                                         /* If it could work, try it. */
 989                                         if (nextch == '\0' || *reginput == nextch)
 990                                                 if (regmatch(next))
 991                                                         return(1);
 992                                         /* Couldn't or didn't -- back up. */
 993                                         no--;
 994                                         reginput = save + no;
 995                                 }
 996                                 return(0);
 997                         }
 998                         /* NOTREACHED */
 999                         break;
1000                 case END:
1001                         return(1);      /* Success! */
1002                         /* NOTREACHED */
1003                         break;
1004                 default:
1005                         regerror("memory corruption");
1006                         return(0);
1007                         /* NOTREACHED */
1008                         break;
1009                 }
1010
1011                 scan = next;
1012         }
1013
1014         /*
1015          * We get here only if there's trouble -- normally "case END" is
1016          * the terminating point.
1017          */
1018         regerror("corrupted pointers");
1019         return(0);
1020 }
1021
1022 /*
1023  - regrepeat - repeatedly match something simple, report how many
1024  */
1025 static int
1026 regrepeat(p)
1027 char *p;
1028 {
1029         register int count = 0;
1030         register char *scan;
1031         register char *opnd;
1032
1033         scan = reginput;
1034         opnd = OPERAND(p);
1035         switch (OP(p)) {
1036         case ANY:
1037                 count = strlen(scan);
1038                 scan += count;
1039                 break;
1040         case EXACTLY:
1041                 while (*opnd == *scan) {
1042                         count++;
1043                         scan++;
1044                 }
1045                 break;
1046         case ANYOF:
1047                 while (*scan != '\0' && strchr(opnd, *scan) != NULL) {
1048                         count++;
1049                         scan++;
1050                 }
1051                 break;
1052         case ANYBUT:
1053                 while (*scan != '\0' && strchr(opnd, *scan) == NULL) {
1054                         count++;
1055                         scan++;
1056                 }
1057                 break;
1058         default:                /* Oh dear.  Called inappropriately. */
1059                 regerror("internal foulup");
1060                 count = 0;      /* Best compromise. */
1061                 break;
1062         }
1063         reginput = scan;
1064
1065         return(count);
1066 }
1067
1068 /*
1069  - regnext - dig the "next" pointer out of a node
1070  */
1071 static char *
1072 regnext(p)
1073 register char *p;
1074 {
1075         register int offset;
1076
1077         if (p == &regdummy)
1078                 return(NULL);
1079
1080         offset = NEXT(p);
1081         if (offset == 0)
1082                 return(NULL);
1083
1084         if (OP(p) == BACK)
1085                 return(p-offset);
1086         else
1087                 return(p+offset);
1088 }
1089
1090 #ifdef DEBUG
1091
1092 STATIC char *regprop();
1093
1094 /*
1095  - regdump - dump a regexp onto stdout in vaguely comprehensible form
1096  */
1097 void
1098 regdump(r)
1099 regexp *r;
1100 {
1101         register char *s;
1102         register char op = EXACTLY;     /* Arbitrary non-END op. */
1103         register char *next;
1104
1105
1106         s = r->program + 1;
1107         while (op != END) {     /* While that wasn't END last time... */
1108                 op = OP(s);
1109                 printf("%2d%s", s-r->program, regprop(s));      /* Where, what. */
1110                 next = regnext(s);
1111                 if (next == NULL)               /* Next ptr. */
1112                         printf("(0)");
1113                 else
1114                         printf("(%d)", (s-r->program)+(next-s));
1115                 s += 3;
1116                 if (op == ANYOF || op == ANYBUT || op == EXACTLY) {
1117                         /* Literal string, where present. */
1118                         while (*s != '\0') {
1119                                 putchar(*s);
1120                                 s++;
1121                         }
1122                         s++;
1123                 }
1124                 putchar('\n');
1125         }
1126
1127         /* Header fields of interest. */
1128         if (r->regstart != '\0')
1129                 printf("start `%c' ", r->regstart);
1130         if (r->reganch)
1131                 printf("anchored ");
1132         if (r->regmust != NULL)
1133                 printf("must have \"%s\"", r->regmust);
1134         printf("\n");
1135 }
1136
1137 /*
1138  - regprop - printable representation of opcode
1139  */
1140 static char *
1141 regprop(op)
1142 char *op;
1143 {
1144         register char *p;
1145         static char buf[50];
1146
1147         (void) strcpy(buf, ":");
1148
1149         switch (OP(op)) {
1150         case BOL:
1151                 p = "BOL";
1152                 break;
1153         case EOL:
1154                 p = "EOL";
1155                 break;
1156         case ANY:
1157                 p = "ANY";
1158                 break;
1159         case ANYOF:
1160                 p = "ANYOF";
1161                 break;
1162         case ANYBUT:
1163                 p = "ANYBUT";
1164                 break;
1165         case BRANCH:
1166                 p = "BRANCH";
1167                 break;
1168         case EXACTLY:
1169                 p = "EXACTLY";
1170                 break;
1171         case NOTHING:
1172                 p = "NOTHING";
1173                 break;
1174         case BACK:
1175                 p = "BACK";
1176                 break;
1177         case END:
1178                 p = "END";
1179                 break;
1180         case OPEN+1:
1181         case OPEN+2:
1182         case OPEN+3:
1183         case OPEN+4:
1184         case OPEN+5:
1185         case OPEN+6:
1186         case OPEN+7:
1187         case OPEN+8:
1188         case OPEN+9:
1189                 sprintf(buf+strlen(buf), "OPEN%d", OP(op)-OPEN);
1190                 p = NULL;
1191                 break;
1192         case CLOSE+1:
1193         case CLOSE+2:
1194         case CLOSE+3:
1195         case CLOSE+4:
1196         case CLOSE+5:
1197         case CLOSE+6:
1198         case CLOSE+7:
1199         case CLOSE+8:
1200         case CLOSE+9:
1201                 sprintf(buf+strlen(buf), "CLOSE%d", OP(op)-CLOSE);
1202                 p = NULL;
1203                 break;
1204         case STAR:
1205                 p = "STAR";
1206                 break;
1207         case PLUS:
1208                 p = "PLUS";
1209                 break;
1210         default:
1211                 regerror("corrupted opcode");
1212                 break;
1213         }
1214         if (p != NULL)
1215                 (void) strcat(buf, p);
1216         return(buf);
1217 }
1218 #endif
1219
1220 /*
1221  * The following is provided for those people who do not have strcspn() in
1222  * their C libraries.  They should get off their butts and do something
1223  * about it; at least one public-domain implementation of those (highly
1224  * useful) string routines has been published on Usenet.
1225  */
1226 #ifdef STRCSPN
1227 /*
1228  * strcspn - find length of initial segment of s1 consisting entirely
1229  * of characters not from s2
1230  */
1231
1232 static int
1233 strcspn(s1, s2)
1234 char *s1;
1235 char *s2;
1236 {
1237         register char *scan1;
1238         register char *scan2;
1239         register int count;
1240
1241         count = 0;
1242         for (scan1 = s1; *scan1 != '\0'; scan1++) {
1243                 for (scan2 = s2; *scan2 != '\0';)       /* ++ moved down. */
1244                         if (*scan1 == *scan2++)
1245                                 return(count);
1246                 count++;
1247         }
1248         return(count);
1249 }
1250 #endif