Goto sanos source index

//
// regcomp.c
//
// Compiler for regular expression library
//
// Ported to sanos by Michael Ringgaard.
//
// Copyright 1992, 1993, 1994, 1997 Henry Spencer.  All rights reserved.
// This software is not subject to any license of the American Telephone
// and Telegraph Company or of the Regents of the University of California.
// 
// Permission is granted to anyone to use this software for any purpose on
// any computer system, and to alter it and redistribute it, subject
// to the following restrictions:
// 
// 1. The author is not responsible for the consequences of use of this
//    software, no matter how awful, even if they arise from flaws in it.
// 
// 2. The origin of this software must not be misrepresented, either by
//    explicit claim or by omission.  Since few users ever read sources,
//    credits must appear in the documentation.
// 
// 3. Altered versions must be plainly marked as such, and must not be
//    misrepresented as being the original software.  Since few users
//    ever read sources, credits must appear in the documentation.
// 
// 4. This notice may not be removed or altered.
// 

#include <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <stdlib.h>
#include <regex.h>

#include "regex2.h"

#include "cclass.h"
#include "cname.h"

#ifdef _MSC_VER
#pragma warning(disable: 4018)
#endif

//
// Parse structure, passed up and down to avoid global variables and
// other clumsinesses.
//

#define NPAREN 10

struct parse {
  char *next;           // Next character in RE
  char *end;            // End of string (-> NUL normally)
  int error;            // Has an error been seen?
  sop *strip;           // Malloced strip
  sopno ssize;          // Malloced strip size (allocated)
  sopno slen;           // Malloced strip length (used)
  int ncsalloc;         // Mumber of csets allocated
  struct re_guts *g;
  // We need to remember () 1-9 for back refs
  sopno pbegin[NPAREN]; // -> ( ([0] unused)
  sopno pend[NPAREN];   // -> ) ([0] unused)
};

static void p_ere(struct parse *p, int stop);
static void p_ere_exp(struct parse *p);
static void p_str(struct parse *p);
static void p_bre(struct parse *p, int end1, int end2);
static int p_simp_re(struct parse *p, int starordinary);
static int p_count(struct parse *p);
static void p_bracket(struct parse *p);
static void p_b_term(struct parse *p, cset *cs);
static void p_b_cclass(struct parse *p, cset *cs);
static void p_b_eclass(struct parse *p, cset *cs);
static char p_b_symbol(struct parse *p);
static char p_b_coll_elem(struct parse *p, int endc);
static char othercase(int ch);
static void bothcases(struct parse *p, int ch);
static void ordinary(struct parse *p, int ch);
static void nonnewline(struct parse *p);
static void repeat(struct parse *p, sopno start, int from, int to);
static int seterr(struct parse *p, int e);
static cset *allocset(struct parse *p);
static void freeset(struct parse *p, cset *cs);
static int freezeset(struct parse *p, cset *cs);
static int firstch(struct parse *p, cset *cs);
static int nch(struct parse *p, cset *cs);
static void mcadd(struct parse *p, cset *cs, char *cp);
static void mcsub(cset *cs, char *cp);
static int mcin(cset *cs, char *cp);
static char *mcfind(cset *cs, char *cp);
static void mcinvert(struct parse *p, cset *cs);
static void mccase(struct parse *p, cset *cs);
static int isinsets(struct re_guts *g, int c);
static int samesets(struct re_guts *g, int c1, int c2);
static void categorize(struct parse *p, struct re_guts *g);
static sopno dupl(struct parse *p, sopno start, sopno finish);
static void doemit(struct parse *p, sop op, size_t opnd);
static void doinsert(struct parse *p, sop op, size_t opnd, sopno pos);
static void dofwd(struct parse *p, sopno pos, sop value);
static void enlarge(struct parse *p, sopno size);
static void stripsnug(struct parse *p, struct re_guts *g);
static void findmust(struct parse *p, struct re_guts *g);
static sopno pluscount(struct parse *p, struct re_guts *g);

static char nuls[10];   // Place to point scanner in event of error

//
// Macros for use with parse structure
// BEWARE:  these know that the parse structure is named `p' !!!
//
#define PEEK()            (*p->next)
#define PEEK2()           (*(p->next + 1))
#define MORE()            (p->next < p->end)
#define MORE2()           (p->next + 1 < p->end)
#define SEE(c)            (MORE() && PEEK() == (c))
#define SEETWO(a, b)      (MORE() && MORE2() && PEEK() == (a) && PEEK2() == (b))
#define EAT(c)            ((SEE(c)) ? (NEXT(), 1) : 0)
#define EATTWO(a, b)      ((SEETWO(a, b)) ? (NEXT2(), 1) : 0)
#define NEXT()            (p->next++)
#define NEXT2()           (p->next += 2)
#define NEXTn(n)          (p->next += (n))
#define GETNEXT()         (*p->next++)
#define SETERROR(e)       seterr(p, (e))
#define REQUIRE(co, e)    ((co) || SETERROR(e))
#define MUSTSEE(c, e)     (REQUIRE(MORE() && PEEK() == (c), e))
#define MUSTEAT(c, e)     (REQUIRE(MORE() && GETNEXT() == (c), e))
#define MUSTNOTSEE(c, e)  (REQUIRE(!MORE() || PEEK() != (c), e))
#define EMIT(op, sopnd)   doemit(p, (sop)(op), (size_t)(sopnd))
#define INSERT(op, pos)   doinsert(p, (sop)(op), HERE()-(pos)+1, pos)
#define AHEAD(pos)        dofwd(p, pos, HERE()-(pos))
#define ASTERN(sop, pos)  EMIT(sop, HERE()-pos)
#define HERE()            (p->slen)
#define THERE()           (p->slen - 1)
#define THERETHERE()      (p->slen - 2)
#define DROP(n)           (p->slen -= (n))

#ifndef NDEBUG
static int never = 0;   // For use in asserts; shuts lint up
#else
#define never 0         // Some <assert.h>s have bugs too
#endif

#ifdef REDEBUG
#define GOODFLAGS(f) (f)
#else
#define GOODFLAGS(f) ((f) & ~REG_DUMP)
#endif

//
// regcomp - interface for parser and compilation
// 
// Returns 0 on success, otherwise REG_something
//
int regcomp(regex_t *preg, const char *pattern, int cflags) {
  struct parse pa;
  struct re_guts *g;
  struct parse *p = &pa;
  int i;
  size_t len;

  cflags = GOODFLAGS(cflags);
  if ((cflags & REG_EXTENDED) && (cflags & REG_NOSPEC)) return REG_INVARG;

  if (cflags & REG_PEND) {
    if (preg->re_endp < pattern) return REG_INVARG;
    len = preg->re_endp - pattern;
  } else {
    len = strlen(pattern);
  }

  // Do the mallocs early so failure handling is easy
  g = (struct re_guts *) malloc(sizeof(struct re_guts) + (NC - 1) * sizeof(cat_t));
  if (g == NULL) return REG_ESPACE;
  p->ssize = len / 2* 3 +  1; // ugh
  p->strip = (sop *) malloc(p->ssize * sizeof(sop));
  p->slen = 0;
  if (p->strip == NULL) {
    free(g);
    return REG_ESPACE;
  }

  // Set things up
  p->g = g;
  p->next = (char *) pattern;  // Convenience; we do not modify it
  p->end = p->next + len;
  p->error = 0;
  p->ncsalloc = 0;
  for (i = 0; i < NPAREN; i++) {
    p->pbegin[i] = 0;
    p->pend[i] = 0;
  }
  g->csetsize = NC;
  g->sets = NULL;
  g->setbits = NULL;
  g->ncsets = 0;
  g->cflags = cflags;
  g->iflags = 0;
  g->nbol = 0;
  g->neol = 0;
  g->must = NULL;
  g->mlen = 0;
  g->nsub = 0;
  g->ncategories = 1; // Category 0 is "everything else"
  g->categories = &g->catspace[-(CHAR_MIN)];
  memset(g->catspace, 0, NC * sizeof(cat_t));
  g->backrefs = 0;

  // Do it
  EMIT(OEND, 0);
  g->firststate = THERE();
  if (cflags & REG_EXTENDED) {
    p_ere(p, OUT);
  } else if (cflags & REG_NOSPEC) {
    p_str(p);
  } else {
    p_bre(p, OUT, OUT);
  }
  EMIT(OEND, 0);
  g->laststate = THERE();

  // Tidy up loose ends and fill things in
  categorize(p, g);
  stripsnug(p, g);
  findmust(p, g);
  g->nplus = pluscount(p, g);
  g->magic = MAGIC2;
  preg->re_nsub = g->nsub;
  preg->re_g = g;
  preg->re_magic = MAGIC1;
#ifndef REDEBUG
  // Not debugging, so can't rely on the assert() in regexec()
  if (g->iflags & BAD) SETERROR(REG_ASSERT);
#endif

  // Win or lose, we're done
  if (p->error != 0) regfree(preg); // lose
  return p->error;
}

//
// p_ere - ERE parser top level, concatenation and alternation
//
static void p_ere(struct parse *p, int stop) {
  char c;
  sopno prevback;
  sopno prevfwd;
  sopno conc;
  int first = 1;   // Is this the first alternative?

  for (;;) {
    // Do a bunch of concatenated expressions
    conc = HERE();
    while (MORE() && (c = PEEK()) != '|' && c != stop) p_ere_exp(p);
    REQUIRE(HERE() != conc, REG_EMPTY); // require nonempty

    if (!EAT('|')) break; // NOTE BREAK OUT

    if (first) {
      INSERT(OCH_, conc); // offset is wrong
      prevfwd = conc;
      prevback = conc;
      first = 0;
    }
    ASTERN(OOR1, prevback);
    prevback = THERE();
    AHEAD(prevfwd);     // fix previous offset
    prevfwd = HERE();
    EMIT(OOR2, 0);      // offset is very wrong
  }

  if (!first) {
    // tail-end fixups
    AHEAD(prevfwd);
    ASTERN(O_CH, prevback);
  }

  assert(!MORE() || SEE(stop));
}

//
// p_ere_exp - parse one subERE, an atom possibly followed by a repetition op
//
static void p_ere_exp(struct parse *p) {
  char c;
  sopno pos;
  int count;
  int count2;
  sopno subno;
  int wascaret = 0;

  assert(MORE());   // Caller should have ensured this
  c = GETNEXT();

  pos = HERE();
  switch (c) {
    case '(':
      REQUIRE(MORE(), REG_EPAREN);
      p->g->nsub++;
      subno = p->g->nsub;
      if (subno < NPAREN) p->pbegin[subno] = HERE();
      EMIT(OLPAREN, subno);
      if (!SEE(')')) p_ere(p, ')');
      if (subno < NPAREN) {
        p->pend[subno] = HERE();
        assert(p->pend[subno] != 0);
      }
      EMIT(ORPAREN, subno);
      MUSTEAT(')', REG_EPAREN);
      break;

#ifndef POSIX_MISTAKE
    case ')':   // Happens only if no current unmatched (
      //
      // You may ask, why the ifndef?  Because I didn't notice
      // this until slightly too late for 1003.2, and none of the
      // other 1003.2 regular-expression reviewers noticed it at
      // all.  So an unmatched ) is legal POSIX, at least until
      // we can get it fixed.
      SETERROR(REG_EPAREN);
      break;
#endif

    case '^':
      EMIT(OBOL, 0);
      p->g->iflags |= USEBOL;
      p->g->nbol++;
      wascaret = 1;
      break;

    case '$':
      EMIT(OEOL, 0);
      p->g->iflags |= USEEOL;
      p->g->neol++;
      break;

    case '|':
      SETERROR(REG_EMPTY);
      break;

    case '*':
    case '+':
    case '?':
      SETERROR(REG_BADRPT);
      break;

    case '.':
      if (p->g->cflags&REG_NEWLINE)
        nonnewline(p);
      else
        EMIT(OANY, 0);
      break;

    case '[':
      p_bracket(p);
      break;

    case '\\':
      REQUIRE(MORE(), REG_EESCAPE);
      c = GETNEXT();
      ordinary(p, c);
      break;

    case '{':   // Okay as ordinary except if digit follows
      REQUIRE(!MORE() || !isdigit(PEEK()), REG_BADRPT);
      // FALLTHROUGH

    default:
      ordinary(p, c);
      break;
  }

  if (!MORE()) return;
  c = PEEK();
  // We call { a repetition if followed by a digit
  if (!( c == '*' || c == '+' || c == '?' || (c == '{' && MORE2() && isdigit(PEEK2())))) return; // No repetition, we're done
  NEXT();

  REQUIRE(!wascaret, REG_BADRPT);
  switch (c) {
    case '*': // Implemented as +?
      // This case does not require the (y|) trick, noKLUDGE
      INSERT(OPLUS_, pos);
      ASTERN(O_PLUS, pos);
      INSERT(OQUEST_, pos);
      ASTERN(O_QUEST, pos);
      break;

    case '+':
      INSERT(OPLUS_, pos);
      ASTERN(O_PLUS, pos);
      break;

    case '?':
      // KLUDGE: emit y? as (y|) until subtle bug gets fixed
      INSERT(OCH_, pos);    // offset slightly wrong
      ASTERN(OOR1, pos);    // this one's right
      AHEAD(pos);           // fix the OCH_
      EMIT(OOR2, 0);        // offset very wrong...
      AHEAD(THERE());       // ...so fix it
      ASTERN(O_CH, THERETHERE());
      break;

    case '{':
      count = p_count(p);
      if (EAT(',')) {
        if (isdigit(PEEK())) {
          count2 = p_count(p);
          REQUIRE(count <= count2, REG_BADBR);
        } else {
          // Single number with comma
          count2 = INFINITY;
        }
      } else {
        // Just a single number
        count2 = count;
      }

      repeat(p, pos, count, count2);
      if (!EAT('}')) {  
        // Error heuristics
        while (MORE() && PEEK() != '}') NEXT();
        REQUIRE(MORE(), REG_EBRACE);
        SETERROR(REG_BADBR);
      }
      break;
  }

  if (!MORE()) return;
  c = PEEK();
  if (!( c == '*' || c == '+' || c == '?' || (c == '{' && MORE2() && isdigit(PEEK2())))) return;
  SETERROR(REG_BADRPT);
}

//
// p_str - string (no metacharacters) "parser"
//
static void p_str(struct parse *p) {
  REQUIRE(MORE(), REG_EMPTY);
  while (MORE()) ordinary(p, GETNEXT());
}

//
// p_bre - BRE parser top level, anchoring and concatenation
//
// Giving end1 as OUT essentially eliminates the end1/end2 check.
//
// This implementation is a bit of a kludge, in that a trailing $ is first
// taken as an ordinary character and then revised to be an anchor.  The
// only undesirable side effect is that '$' gets included as a character
// category in such cases.  This is fairly harmless; not worth fixing.
// The amount of lookahead needed to avoid this kludge is excessive.
static void p_bre(struct parse *p, int end1, int end2) {
  sopno start = HERE();
  int first = 1;     // first subexpression?
  int wasdollar = 0;

  if (EAT('^')) {
    EMIT(OBOL, 0);
    p->g->iflags |= USEBOL;
    p->g->nbol++;
  }
  while (MORE() && !SEETWO(end1, end2)) {
    wasdollar = p_simp_re(p, first);
    first = 0;
  }
  if (wasdollar) {
    // Ops, that was a trailing anchor
    DROP(1);
    EMIT(OEOL, 0);
    p->g->iflags |= USEEOL;
    p->g->neol++;
  }

  REQUIRE(HERE() != start, REG_EMPTY);  // Require nonempty
}

//
// p_simp_re - parse a simple RE, an atom possibly followed by a repetition
//

#define BACKSL (1 << CHAR_BIT)

static int p_simp_re(struct parse *p, int starordinary) {
  int c;
  int count;
  int count2;
  sopno pos;
  int i;
  sopno subno;

  pos = HERE();   // Repetion op, if any, covers from here

  assert(MORE()); // Caller should have ensured this
  c = GETNEXT();
  if (c == '\\') {
    REQUIRE(MORE(), REG_EESCAPE);
    c = BACKSL | (unsigned char) GETNEXT();
  }
  switch (c) {
    case '.':
      if (p->g->cflags&REG_NEWLINE)
        nonnewline(p);
      else
        EMIT(OANY, 0);
      break;

    case '[':
      p_bracket(p);
      break;

    case BACKSL | '{':
      SETERROR(REG_BADRPT);
      break;

    case BACKSL | '(':
      p->g->nsub++;
      subno = p->g->nsub;
      if (subno < NPAREN) p->pbegin[subno] = HERE();
      EMIT(OLPAREN, subno);
      // The MORE here is an error heuristic
      if (MORE() && !SEETWO('\\', ')')) p_bre(p, '\\', ')');
      if (subno < NPAREN) {
        p->pend[subno] = HERE();
        assert(p->pend[subno] != 0);
      }
      EMIT(ORPAREN, subno);
      REQUIRE(EATTWO('\\', ')'), REG_EPAREN);
      break;

    case BACKSL | ')':  // Should not get here -- must be user
    case BACKSL | '}':
      SETERROR(REG_EPAREN);
      break;

    case BACKSL | '1':
    case BACKSL | '2':
    case BACKSL | '3':
    case BACKSL | '4':
    case BACKSL | '5':
    case BACKSL | '6':
    case BACKSL | '7':
    case BACKSL | '8':
    case BACKSL | '9':
      i = (c & ~BACKSL) - '0';
      assert(i < NPAREN);
      if (p->pend[i] != 0) {
        assert(i <= p->g->nsub);
        EMIT(OBACK_, i);
        assert(p->pbegin[i] != 0);
        assert(OP(p->strip[p->pbegin[i]]) == OLPAREN);
        assert(OP(p->strip[p->pend[i]]) == ORPAREN);
        dupl(p, p->pbegin[i] + 1, p->pend[i]);
        EMIT(O_BACK, i);
      } else {
        SETERROR(REG_ESUBREG);
      }
      p->g->backrefs = 1;
      break;

    case '*':
      REQUIRE(starordinary, REG_BADRPT);
      // FALLTHROUGH

    default:
      ordinary(p, (char) c); // Takes off BACKSL, if any
      break;
  }

  if (EAT('*')) {
    // Implemented as +?
    // This case does not require the (y|) trick, noKLUDGE
    INSERT(OPLUS_, pos);
    ASTERN(O_PLUS, pos);
    INSERT(OQUEST_, pos);
    ASTERN(O_QUEST, pos);
  } else if (EATTWO('\\', '{')) {
    count = p_count(p);
    if (EAT(',')) {
      if (MORE() && isdigit(PEEK())) {
        count2 = p_count(p);
        REQUIRE(count <= count2, REG_BADBR);
      } else {
        // Single number with comma
        count2 = INFINITY;
      }
    } else {
      // just a single number
      count2 = count;
    }
    repeat(p, pos, count, count2);
    if (!EATTWO('\\', '}')) { 
      // Error heuristics
      while (MORE() && !SEETWO('\\', '}')) NEXT();
      REQUIRE(MORE(), REG_EBRACE);
      SETERROR(REG_BADBR);
    }
  } else if (c == (unsigned char)'$') { 
    // $ (but not \$) ends it
    return 1;
  }

  return 0;
}

//
// p_count - parse a repetition count
//
static int p_count(struct parse *p) {
  int count = 0;
  int ndigits = 0;

  while (MORE() && isdigit(PEEK()) && count <= DUPMAX) {
    count = count * 10 + (GETNEXT() - '0');
    ndigits++;
  }

  REQUIRE(ndigits > 0 && count <= DUPMAX, REG_BADBR);
  return count;
}

//
// p_bracket - parse a bracketed character list
//
// Note a significant property of this code:  if the allocset() did SETERROR,
// no set operations are done.
//
static void p_bracket(struct parse *p) {
  cset *cs = allocset(p);
  int invert = 0;

  // Dept of Truly Sickening Special-Case Kludges
  if (p->next + 5 < p->end && strncmp(p->next, "[:<:]]", 6) == 0) {
    EMIT(OBOW, 0);
    NEXTn(6);
    return;
  }
  if (p->next + 5 < p->end && strncmp(p->next, "[:>:]]", 6) == 0) {
    EMIT(OEOW, 0);
    NEXTn(6);
    return;
  }

  if (EAT('^')) invert++; // Make note to invert set at end
  if (EAT(']')) {
    CHadd(cs, ']');
  } else if (EAT('-')) {
    CHadd(cs, '-');
  }
  while (MORE() && PEEK() != ']' && !SEETWO('-', ']')) p_b_term(p, cs);
  if (EAT('-')) CHadd(cs, '-');
  MUSTEAT(']', REG_EBRACK);

  if (p->error != 0) return;  // Don't mess things up further

  if (p->g->cflags & REG_ICASE) {
    int i;
    int ci;

    for (i = p->g->csetsize - 1; i >= 0; i--) {
      if (CHIN(cs, i) && isalpha(i)) {
        ci = othercase(i);
        if (ci != i) CHadd(cs, ci);
      }
    }
    if (cs->multis != NULL) mccase(p, cs);
  }
  if (invert) {
    int i;

    for (i = p->g->csetsize - 1; i >= 0; i--) {
      if (CHIN(cs, i)) {
        CHsub(cs, i);
      } else {
        CHadd(cs, i);
      }
    }
    if (p->g->cflags & REG_NEWLINE) CHsub(cs, '\n');
    if (cs->multis != NULL) mcinvert(p, cs);
  }

  assert(cs->multis == NULL);   // xxx

  if (nch(p, cs) == 1) {
    // Optimize singleton sets
    ordinary(p, firstch(p, cs));
    freeset(p, cs);
  } else {
    EMIT(OANYOF, freezeset(p, cs));
  }
}

//
// p_b_term - parse one term of a bracketed character list
//
static void p_b_term(struct parse *p, cset *cs) {
  char c;
  char start, finish;
  int i;

  // classify what we've got
  switch ((MORE()) ? PEEK() : '\0') {
    case '[':
      c = (MORE2()) ? PEEK2() : '\0';
      break;

    case '-':
      SETERROR(REG_ERANGE);
      return;     // NOTE RETURN
      break;

    default:
      c = '\0';
      break;
  }

  switch (c) {
    case ':':   // character class
      NEXT2();
      REQUIRE(MORE(), REG_EBRACK);
      c = PEEK();
      REQUIRE(c != '-' && c != ']', REG_ECTYPE);
      p_b_cclass(p, cs);
      REQUIRE(MORE(), REG_EBRACK);
      REQUIRE(EATTWO(':', ']'), REG_ECTYPE);
      break;

    case '=':   // equivalence class
      NEXT2();
      REQUIRE(MORE(), REG_EBRACK);
      c = PEEK();
      REQUIRE(c != '-' && c != ']', REG_ECOLLATE);
      p_b_eclass(p, cs);
      REQUIRE(MORE(), REG_EBRACK);
      REQUIRE(EATTWO('=', ']'), REG_ECOLLATE);
      break;

    default:    // symbol, ordinary character, or range
      // xxx revision needed for multichar stuff
      start = p_b_symbol(p);
      if (SEE('-') && MORE2() && PEEK2() != ']') {
        // range
        NEXT();
        if (EAT('-')) {
          finish = '-';
        } else {
          finish = p_b_symbol(p);
        }
      } else {
        finish = start;
      }
      // xxx what about signed chars here...
      REQUIRE((uch) start <= (uch) finish, REG_ERANGE);
      for (i = (uch) start; i <= (uch) finish; i++) CHadd(cs, i);
      break;
  }
}

//
// p_b_cclass - parse a character-class name and deal with it
//
static void p_b_cclass(struct parse *p, cset *cs) {
  char *sp = p->next;
  struct cclass *cp;
  size_t len;
  char *u;
  char c;

  while (MORE() && isalpha(PEEK())) NEXT();
  len = p->next - sp;
  for (cp = cclasses; cp->name != NULL; cp++) {
    if (strncmp(cp->name, sp, len) == 0 && cp->name[len] == '\0') break;
  }
  if (cp->name == NULL) {
    // Oops, didn't find it
    SETERROR(REG_ECTYPE);
    return;
  }

  u = cp->chars;
  while ((c = *u++) != '\0') CHadd(cs, c);
  for (u = cp->multis; *u != '\0'; u += strlen(u) + 1) MCadd(p, cs, u);
}

//
// p_b_eclass - parse an equivalence-class name and deal with it
//
// This implementation is incomplete. xxx
//
static void p_b_eclass(struct parse *p, cset *cs) {
  char c;

  c = p_b_coll_elem(p, '=');
  CHadd(cs, c);
}

//
// p_b_symbol - parse a character or [..]ed multicharacter collating symbol
//
static char p_b_symbol(struct parse *p) {
  char value;

  REQUIRE(MORE(), REG_EBRACK);
  if (!EATTWO('[', '.')) return GETNEXT();

  // Collating symbol
  value = p_b_coll_elem(p, '.');
  REQUIRE(EATTWO('.', ']'), REG_ECOLLATE);
  return value;
}


//
// p_b_coll_elem - parse a collating-element name and look it up
//
static char p_b_coll_elem(struct parse *p, int endc) {
  char *sp = p->next;
  struct cname *cp;
  int len;

  while (MORE() && !SEETWO(endc, ']')) NEXT();
  if (!MORE()) {
    SETERROR(REG_EBRACK);
    return 0;
  }
  len = p->next - sp;
  for (cp = cnames; cp->name != NULL; cp++) {
    if (strncmp(cp->name, sp, len) == 0 && cp->name[len] == '\0') return cp->code; // known name
  }
  if (len == 1) return *sp;  // single character
  SETERROR(REG_ECOLLATE);     // neither
  return 0;
}

//
// othercase - return the case counterpart of an alphabetic
// 
static char othercase(int ch) {
  assert(isalpha(ch));
  if (isupper(ch)) {
    return tolower(ch);
  } else if (islower(ch)) {
    return toupper(ch);
  } else {
    // peculiar, but could happen
    return ch;
  }
}

//
// bothcases - emit a dualcase version of a two-case character
//
// Boy, is this implementation ever a kludge...
//
static void bothcases(struct parse *p, int ch) {
  char *oldnext = p->next;
  char *oldend = p->end;
  char bracket[3];

  assert(othercase(ch) != ch);  // p_bracket() would recurse
  p->next = bracket;
  p->end = bracket + 2;
  bracket[0] = ch;
  bracket[1] = ']';
  bracket[2] = '\0';
  p_bracket(p);
  assert(p->next == bracket + 2);
  p->next = oldnext;
  p->end = oldend;
}

//
// ordinary - emit an ordinary character
// 
static void ordinary(struct parse *p, int ch) {
  cat_t *cap = p->g->categories;

  if ((p->g->cflags & REG_ICASE) && isalpha(ch) && othercase(ch) != ch) {
    bothcases(p, ch);
  } else {
    EMIT(OCHAR, (unsigned char)ch);
    if (cap[ch] == 0) cap[ch] = p->g->ncategories++;
  }
}

//
// nonnewline - emit REG_NEWLINE version of OANY
//
// Boy, is this implementation ever a kludge...
//
static void nonnewline(struct parse *p) {
  char *oldnext = p->next;
  char *oldend = p->end;
  char bracket[4];

  p->next = bracket;
  p->end = bracket + 3;
  bracket[0] = '^';
  bracket[1] = '\n';
  bracket[2] = ']';
  bracket[3] = '\0';
  p_bracket(p);
  assert(p->next == bracket + 3);
  p->next = oldnext;
  p->end = oldend;
}

//
// repeat - generate code for a bounded repetition, recursively if needed
//

#define N         2
#define INF       3
#define REP(f, t) ((f) * 8 + (t))
#define MAP(n)    (((n) <= 1) ? (n) : ((n) == INFINITY) ? INF : N)

static void repeat(struct parse *p, sopno start, int from, int to) {
  sopno finish = HERE();
  sopno copy;

  if (p->error != 0) return; // Head off possible runaway recursion
  assert(from <= to);

  switch (REP(MAP(from), MAP(to))) {
    case REP(0, 0):     // must be user doing this
      DROP(finish - start); // drop the operand
      break;
      
    case REP(0, 1):     // as x{1,1}?
    case REP(0, N):     // as x{1,n}?
    case REP(0, INF):   // as x{1,}?
      // KLUDGE: emit y? as (y|) until subtle bug gets fixed
      INSERT(OCH_, start);    // offset is wrong...
      repeat(p, start + 1, 1, to);
      ASTERN(OOR1, start);
      AHEAD(start);     // ... fix it
      EMIT(OOR2, 0);
      AHEAD(THERE());
      ASTERN(O_CH, THERETHERE());
      break;

    case REP(1, 1):     // trivial case
      // done
      break;

    case REP(1, N):     // as x?x{1,n-1}
      // KLUDGE: emit y? as (y|) until subtle bug gets fixed
      INSERT(OCH_, start);
      ASTERN(OOR1, start);
      AHEAD(start);
      EMIT(OOR2, 0);      // offset very wrong...
      AHEAD(THERE());     // ...so fix it
      ASTERN(O_CH, THERETHERE());
      copy = dupl(p, start + 1, finish + 1);
      assert(copy == finish + 4);
      repeat(p, copy, 1, to - 1);
      break;

    case REP(1, INF):   // as x+
      INSERT(OPLUS_, start);
      ASTERN(O_PLUS, start);
      break;

    case REP(N, N):     // as xx{m-1,n-1}
      copy = dupl(p, start, finish);
      repeat(p, copy, from - 1, to - 1);
      break;

    case REP(N, INF):   // as xx{n-1,INF}
      copy = dupl(p, start, finish);
      repeat(p, copy, from-1, to);
      break;

    default:      // "can't happen"
      SETERROR(REG_ASSERT); // just in case
      break;
  }
}

//
// seterr - set an error condition
//
static int seterr(struct parse *p, int e) {
  if (p->error == 0)p->error = e; // keep earliest error condition
  p->next = nuls;   // try to bring things to a halt
  p->end = nuls;
  return 0;    // make the return value well-defined
}

//
// allocset - allocate a set of characters for []
//
static cset *allocset(struct parse *p) {
  int no = p->g->ncsets++;
  size_t nc;
  size_t nbytes;
  cset *cs;
  size_t css = (size_t) p->g->csetsize;
  int i;

  if (no >= p->ncsalloc) {
    // need another column of space
    p->ncsalloc += CHAR_BIT;
    nc = p->ncsalloc;
    assert(nc % CHAR_BIT == 0);
    nbytes = nc / CHAR_BIT * css;
    if (p->g->sets == NULL) {
      p->g->sets = (cset *) malloc(nc * sizeof(cset));
    } else {
      p->g->sets = (cset *) realloc(p->g->sets, nc * sizeof(cset));
    }
    if (p->g->setbits == NULL) {
      p->g->setbits = (uch *) malloc(nbytes);
    } else {
      p->g->setbits = (uch *) realloc(p->g->setbits, nbytes);
      // xxx this isn't right if setbits is now NULL
      for (i = 0; i < no; i++) p->g->sets[i].ptr = p->g->setbits + css * (i / CHAR_BIT);
    }
    if (p->g->sets != NULL && p->g->setbits != NULL) {
      memset(p->g->setbits + (nbytes - css), 0, css);
    } else {
      no = 0;
      SETERROR(REG_ESPACE);
      // caller's responsibility not to do set ops
    }
  }

  assert(p->g->sets != NULL); // xxx
  cs = &p->g->sets[no];
  cs->ptr = p->g->setbits + css * ((no) / CHAR_BIT);
  cs->mask = 1 << ((no) % CHAR_BIT);
  cs->hash = 0;
  cs->smultis = 0;
  cs->multis = NULL;

  return cs;
}

//
// freeset - free a now-unused set
//
static void freeset(struct parse *p, cset *cs) {
  int i;
  cset *top = &p->g->sets[p->g->ncsets];
  size_t css = (size_t) p->g->csetsize;

  for (i = 0; i < css; i++) CHsub(cs, i);
  if (cs == top-1) p->g->ncsets--; // recover only the easy case
}

//
// freezeset - final processing on a set of characters
//
// The main task here is merging identical sets.  This is usually a waste
// of time (although the hash code minimizes the overhead), but can win
// big if REG_ICASE is being used.  REG_ICASE, by the way, is why the hash
// is done using addition rather than xor -- all ASCII [aA] sets xor to
// the same value!
static int freezeset(struct parse *p, cset *cs) {
  uch h = cs->hash;
  int i;
  cset *top = &p->g->sets[p->g->ncsets];
  cset *cs2;
  size_t css = (size_t) p->g->csetsize;

  // Look for an earlier one which is the same
  for (cs2 = &p->g->sets[0]; cs2 < top; cs2++) {
    if (cs2->hash == h && cs2 != cs) {
      // maybe
      for (i = 0; i < css; i++) {
        if (!!CHIN(cs2, i) != !!CHIN(cs, i)) break;    // no
      }
      if (i == css) break; // yes
    }
  }
  if (cs2 < top) {  
    // found one
    freeset(p, cs);
    cs = cs2;
  }

  return cs - p->g->sets;
}

//
// firstch - return first character in a set (which must have at least one)
//
static int firstch(struct parse *p, cset *cs) {
  int i;
  size_t css = (size_t) p->g->csetsize;

  for (i = 0; i < css; i++) {
    if (CHIN(cs, i)) return (char) i;
  }
  assert(never);
  return 0;    // arbitrary
}

//
// nch - number of characters in a set
//
static int nch(struct parse *p, cset *cs) {
  int i;
  size_t css = (size_t) p->g->csetsize;
  int n = 0;

  for (i = 0; i < css; i++) {
    if (CHIN(cs, i)) n++;
  }
  return n;
}

//
// mcadd - add a collating element to a cset
//
static void mcadd(struct parse *p, cset *cs, char *cp) {
  size_t oldend = cs->smultis;

  cs->smultis += strlen(cp) + 1;
  if (cs->multis == NULL) {
    cs->multis = malloc(cs->smultis);
  } else {
    cs->multis = realloc(cs->multis, cs->smultis);
  }

  if (cs->multis == NULL) {
    SETERROR(REG_ESPACE);
    return;
  }

  strcpy(cs->multis + oldend - 1, cp);
  cs->multis[cs->smultis - 1] = '\0';
}

//
// mcsub - subtract a collating element from a cset
//
static void mcsub(cset *cs, char *cp) {
  char *fp = mcfind(cs, cp);
  size_t len = strlen(fp);

  assert(fp != NULL);
  memmove(fp, fp + len + 1, cs->smultis - (fp + len + 1 - cs->multis));
  cs->smultis -= len;

  if (cs->smultis == 0) {
    free(cs->multis);
    cs->multis = NULL;
    return;
  }

  cs->multis = realloc(cs->multis, cs->smultis);
  assert(cs->multis != NULL);
}

//
// mcin - is a collating element in a cset?
//
static int mcin(cset *cs, char *cp) {
  return mcfind(cs, cp) != NULL;
}

//
// mcfind - find a collating element in a cset
//
static char *mcfind(cset *cs, char *cp) {
  char *p;

  if (cs->multis == NULL) return NULL;
  for (p = cs->multis; *p != '\0'; p += strlen(p) + 1) {
    if (strcmp(cp, p) == 0) return p;
  }
  return NULL;
}

//
// mcinvert - invert the list of collating elements in a cset
//
// This would have to know the set of possibilities.  Implementation
// is deferred.
static void mcinvert(struct parse *p, cset *cs) {
  assert(cs->multis == NULL); // xxx
}

//
// mccase - add case counterparts of the list of collating elements in a cset
//
// This would have to know the set of possibilities.  Implementation
// is deferred.
static void mccase(struct parse *p, cset *cs) {
  assert(cs->multis == NULL); // xxx
}

//
// isinsets - is this character in any sets?
//
static int isinsets(struct re_guts *g, int c) {
  uch *col;
  int i;
  int ncols = (g->ncsets + (CHAR_BIT - 1)) / CHAR_BIT;
  unsigned uc = (unsigned char) c;

  for (i = 0, col = g->setbits; i < ncols; i++, col += g->csetsize) {
    if (col[uc] != 0) return 1;
  }
  return 0;
}

//
// samesets - are these two characters in exactly the same sets?
//
static int samesets(struct re_guts *g, int c1, int c2) {
  uch *col;
  int i;
  int ncols = (g->ncsets + (CHAR_BIT - 1)) / CHAR_BIT;
  unsigned uc1 = (unsigned char) c1;
  unsigned uc2 = (unsigned char) c2;

  for (i = 0, col = g->setbits; i < ncols; i++, col += g->csetsize) {
    if (col[uc1] != col[uc2]) return 0;
  }
  return 1;
}

//
// categorize - sort out character categories
//
static void categorize(struct parse *p, struct re_guts *g) {
  cat_t *cats = g->categories;
  int c;
  int c2;
  cat_t cat;

  // Avoid making error situations worse
  if (p->error != 0) return;

  for (c = CHAR_MIN; c <= CHAR_MAX; c++)
  {
    if (cats[c] == 0 && isinsets(g, c)) {
      cat = g->ncategories++;
      cats[c] = cat;
      for (c2 = c + 1; c2 <= CHAR_MAX; c2++) {
        if (cats[c2] == 0 && samesets(g, c, c2)) cats[c2] = cat;
      }
    }
  }
}

//
// dupl - emit a duplicate of a bunch of sops
//
static sopno dupl(struct parse *p, sopno start, sopno finish) {
  sopno ret = HERE();
  sopno len = finish - start;

  assert(finish >= start);
  if (len == 0) return(ret);
  enlarge(p, p->ssize + len); // this many unexpected additions
  assert(p->ssize >= p->slen + len);
  memcpy(p->strip + p->slen, p->strip + start, len * sizeof(sop));
  p->slen += len;
  return ret;
}

//
// doemit - emit a strip operator
//
// It might seem better to implement this as a macro with a function as
// hard-case backup, but it's just too big and messy unless there are
// some changes to the data structures.  Maybe later.
static void doemit(struct parse *p, sop op, size_t opnd) {
  // Avoid making error situations worse
  if (p->error != 0) return;

  // Deal with oversize operands ("can't happen", more or less)
  assert(opnd < 1 << OPSHIFT);

  // Deal with undersized strip
  if (p->slen >= p->ssize) enlarge(p, (p->ssize + 1) / 2 * 3); // +50%
  assert(p->slen < p->ssize);

  // Finally, it's all reduced to the easy case
  p->strip[p->slen++] = SOP(op, opnd);
}

//
// doinsert - insert a sop into the strip
//
static void doinsert(struct parse *p, sop op, size_t opnd, sopno pos) {
  sopno sn;
  sop s;
  int i;

  // Avoid making error situations worse
  if (p->error != 0) return;

  sn = HERE();
  EMIT(op, opnd);   // do checks, ensure space
  assert(HERE() == sn + 1);
  s = p->strip[sn];

  // Adjust paren pointers
  assert(pos > 0);
  for (i = 1; i < NPAREN; i++) {
    if (p->pbegin[i] >= pos)  p->pbegin[i]++;
    if (p->pend[i] >= pos) p->pend[i]++;
  }

  memmove(&p->strip[pos + 1], &p->strip[pos], (HERE() - pos - 1) * sizeof(sop));
  p->strip[pos] = s;
}

//
// dofwd - complete a forward reference
//
static void dofwd(struct parse *p, sopno pos, sop value) {
  // Avoid making error situations worse
  if (p->error != 0) return;

  assert(value < 1 << OPSHIFT);
  p->strip[pos] = OP(p->strip[pos]) | value;
}

//
// enlarge - enlarge the strip
//
static void enlarge(struct parse *p, sopno size) {
  sop *sp;

  if (p->ssize >= size) return;

  sp = (sop *) realloc(p->strip, size * sizeof(sop));
  if (sp == NULL) {
    SETERROR(REG_ESPACE);
    return;
  }
  p->strip = sp;
  p->ssize = size;
}

//
// stripsnug - compact the strip
//
static void stripsnug(struct parse *p, struct re_guts *g) {
  g->nstates = p->slen;
  g->strip = (sop *) realloc(p->strip, p->slen * sizeof(sop));
  if (g->strip == NULL) {
    SETERROR(REG_ESPACE);
    g->strip = p->strip;
  }
}

//
// findmust - fill in must and mlen with longest mandatory literal string
//
// This algorithm could do fancy things like analyzing the operands of |
// for common subsequences.  Someday.  This code is simple and finds most
// of the interesting cases.
//
// Note that must and mlen got initialized during setup.
//
static void findmust(struct parse *p, struct re_guts *g) {
  sop *scan;
  sop *start;
  sop *newstart;
  sopno newlen;
  sop s;
  char *cp;
  sopno i;

  // Avoid making error situations worse
  if (p->error != 0) return;

  // Find the longest OCHAR sequence in strip
  newlen = 0;
  scan = g->strip + 1;
  do {
    s = *scan++;
    switch (OP(s)) {
      case OCHAR:   // sequence member
        if (newlen == 0) newstart = scan - 1;   // new sequence
        newlen++;
        break;

      case OPLUS_:    // things that don't break one
      case OLPAREN:
      case ORPAREN:
        break;

      case OQUEST_:   // things that must be skipped
      case OCH_:
        scan--;
        do {
          scan += OPND(s);
          s = *scan;
          // assert() interferes w debug printouts
          if (OP(s) != O_QUEST && OP(s) != O_CH && OP(s) != OOR2) {
            g->iflags |= BAD;
            return;
          }
        } while (OP(s) != O_QUEST && OP(s) != O_CH);
        // fallthrough
        
      default:    // things that break a sequence
        if (newlen > g->mlen) {
          // ends one
          start = newstart;
          g->mlen = newlen;
        }
        newlen = 0;
        break;
    }
  } while (OP(s) != OEND);

  if (g->mlen == 0) return;  // there isn't one
    

  // Turn it into a character string
  g->must = malloc((size_t) g->mlen + 1);
  if (g->must == NULL) {
    // argh; just forget it
    g->mlen = 0;
    return;
  }
  cp = g->must;
  scan = start;
  for (i = g->mlen; i > 0; i--) {
    while (OP(s = *scan++) != OCHAR) continue;
    assert(cp < g->must + g->mlen);
    *cp++ = (char) OPND(s);
  }
  assert(cp == g->must + g->mlen);
  *cp++ = '\0';   // just on general principles
}

//
// pluscount - count + nesting
//
static sopno pluscount(struct parse *p, struct re_guts *g) {
  sop *scan;
  sop s;
  sopno plusnest = 0;
  sopno maxnest = 0;

  if (p->error != 0) return 0;  // there may not be an OEND

  scan = g->strip + 1;
  do {
    s = *scan++;
    switch (OP(s)) {
      case OPLUS_:
        plusnest++;
        break;

      case O_PLUS:
        if (plusnest > maxnest) maxnest = plusnest;
        plusnest--;
        break;
    }
  } while (OP(s) != OEND);
  if (plusnest != 0) g->iflags |= BAD;
  return maxnest;
}