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unifdef.c

/*
 * Copyright (c) 2002 - 2005 Tony Finch <dot@dotat.at>.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by Dave Yost.
 * It was rewritten to support ANSI C by Tony Finch. The original version of
 * unifdef carried the following copyright notice. None of its code remains
 * in this version (though some of the names remain).
 *
 * Copyright (c) 1985, 1993
 *    The Regents of the University of California.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/cdefs.h>

#ifndef lint
#if 0
static const char copyright[] =
"@(#) Copyright (c) 1985, 1993\n\
      The Regents of the University of California.  All rights reserved.\n";
#endif
#ifdef __IDSTRING
__IDSTRING(Berkeley, "@(#)unifdef.c 8.1 (Berkeley) 6/6/93");
__IDSTRING(NetBSD, "$NetBSD: unifdef.c,v 1.8 2000/07/03 02:51:36 matt Exp $");
__IDSTRING(dotat, "$dotat: things/unifdef.c,v 1.171 2005/03/08 12:38:48 fanf2 Exp $");
#endif
#endif /* not lint */
#ifdef __FBSDID
__FBSDID("$FreeBSD: /repoman/r/ncvs/src/usr.bin/unifdef/unifdef.c,v 1.20 2005/05/21 09:55:09 ru Exp $");
#endif

/*
 * unifdef - remove ifdef'ed lines
 *
 *  Wishlist:
 *      provide an option which will append the name of the
 *        appropriate symbol after #else's and #endif's
 *      provide an option which will check symbols after
 *        #else's and #endif's to see that they match their
 *        corresponding #ifdef or #ifndef
 *
 *   The first two items above require better buffer handling, which would
 *     also make it possible to handle all "dodgy" directives correctly.
 */

#include <ctype.h>
#include <err.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

size_t strlcpy(char *dst, const char *src, size_t siz);

/* types of input lines: */
typedef enum {
      LT_TRUEI,         /* a true #if with ignore flag */
      LT_FALSEI,        /* a false #if with ignore flag */
      LT_IF,                  /* an unknown #if */
      LT_TRUE,          /* a true #if */
      LT_FALSE,         /* a false #if */
      LT_ELIF,          /* an unknown #elif */
      LT_ELTRUE,        /* a true #elif */
      LT_ELFALSE,       /* a false #elif */
      LT_ELSE,          /* #else */
      LT_ENDIF,         /* #endif */
      LT_DODGY,         /* flag: directive is not on one line */
      LT_DODGY_LAST = LT_DODGY + LT_ENDIF,
      LT_PLAIN,         /* ordinary line */
      LT_EOF,                 /* end of file */
      LT_COUNT
} Linetype;

static char const * const linetype_name[] = {
      "TRUEI", "FALSEI", "IF", "TRUE", "FALSE",
      "ELIF", "ELTRUE", "ELFALSE", "ELSE", "ENDIF",
      "DODGY TRUEI", "DODGY FALSEI",
      "DODGY IF", "DODGY TRUE", "DODGY FALSE",
      "DODGY ELIF", "DODGY ELTRUE", "DODGY ELFALSE",
      "DODGY ELSE", "DODGY ENDIF",
      "PLAIN", "EOF"
};

/* state of #if processing */
typedef enum {
      IS_OUTSIDE,
      IS_FALSE_PREFIX,  /* false #if followed by false #elifs */
      IS_TRUE_PREFIX,         /* first non-false #(el)if is true */
      IS_PASS_MIDDLE,         /* first non-false #(el)if is unknown */
      IS_FALSE_MIDDLE,  /* a false #elif after a pass state */
      IS_TRUE_MIDDLE,         /* a true #elif after a pass state */
      IS_PASS_ELSE,           /* an else after a pass state */
      IS_FALSE_ELSE,          /* an else after a true state */
      IS_TRUE_ELSE,           /* an else after only false states */
      IS_FALSE_TRAILER, /* #elifs after a true are false */
      IS_COUNT
} Ifstate;

static char const * const ifstate_name[] = {
      "OUTSIDE", "FALSE_PREFIX", "TRUE_PREFIX",
      "PASS_MIDDLE", "FALSE_MIDDLE", "TRUE_MIDDLE",
      "PASS_ELSE", "FALSE_ELSE", "TRUE_ELSE",
      "FALSE_TRAILER"
};

/* state of comment parser */
typedef enum {
      NO_COMMENT = false,     /* outside a comment */
      C_COMMENT,        /* in a comment like this one */
      CXX_COMMENT,            /* between // and end of line */
      STARTING_COMMENT, /* just after slash-backslash-newline */
      FINISHING_COMMENT,      /* star-backslash-newline in a C comment */
      CHAR_LITERAL,           /* inside '' */
      STRING_LITERAL          /* inside "" */
} Comment_state;

static char const * const comment_name[] = {
      "NO", "C", "CXX", "STARTING", "FINISHING", "CHAR", "STRING"
};

/* state of preprocessor line parser */
typedef enum {
      LS_START,         /* only space and comments on this line */
      LS_HASH,          /* only space, comments, and a hash */
      LS_DIRTY          /* this line can't be a preprocessor line */
} Line_state;

static char const * const linestate_name[] = {
      "START", "HASH", "DIRTY"
};

/*
 * Minimum translation limits from ISO/IEC 9899:1999 5.2.4.1
 */
#define     MAXDEPTH        64                  /* maximum #if nesting */
#define     MAXLINE         4096                /* maximum length of line */
#define     MAXSYMS         4096                /* maximum number of symbols */

/*
 * Sometimes when editing a keyword the replacement text is longer, so
 * we leave some space at the end of the tline buffer to accommodate this.
 */
#define     EDITSLOP        10

/*
 * Globals.
 */

static bool             complement;       /* -c: do the complement */
static bool             debugging;        /* -d: debugging reports */
static bool             iocccok;          /* -e: fewer IOCCC errors */
static bool             killconsts;       /* -k: eval constant #ifs */
static bool             lnblank;          /* -l: blank deleted lines */
static bool             lnnum;                  /* -n: add #line directives */
static bool             symlist;          /* -s: output symbol list */
static bool             text;             /* -t: this is a text file */

static const char      *symname[MAXSYMS]; /* symbol name */
static const char      *value[MAXSYMS];         /* -Dsym=value */
static bool             ignore[MAXSYMS];  /* -iDsym or -iUsym */
static int              nsyms;                  /* number of symbols */

static FILE            *input;                  /* input file pointer */
static const char      *filename;         /* input file name */
static int              linenum;          /* current line number */

static char             tline[MAXLINE+EDITSLOP];/* input buffer plus space */
static char            *keyword;          /* used for editing #elif's */

static Comment_state    incomment;        /* comment parser state */
static Line_state       linestate;        /* #if line parser state */
static Ifstate          ifstate[MAXDEPTH];      /* #if processor state */
static bool             ignoring[MAXDEPTH];     /* ignore comments state */
static int              stifline[MAXDEPTH];     /* start of current #if */
static int              depth;                  /* current #if nesting */
static int              delcount;         /* count of deleted lines */
static bool             keepthis;         /* don't delete constant #if */

static int              exitstat;         /* program exit status */

static void             addsym(bool, bool, char *);
static void             debug(const char *, ...);
static void             done(void);
static void             error(const char *);
static int              findsym(const char *);
static void             flushline(bool);
static Linetype         getline(void);
static Linetype         ifeval(const char **);
static void             ignoreoff(void);
static void             ignoreon(void);
static void             keywordedit(const char *);
static void             nest(void);
static void             process(void);
static const char      *skipcomment(const char *);
static const char      *skipsym(const char *);
static void             state(Ifstate);
static int              strlcmp(const char *, const char *, size_t);
static void             unnest(void);
static void             usage(void);

#define endsym(c) (!isalpha((unsigned char)c) && !isdigit((unsigned char)c) && c != '_')

/*
 * The main program.
 */
int
main(int argc, char *argv[])
{
      int opt;

      while ((opt = getopt(argc, argv, "i:D:U:I:cdeklnst")) != -1)
            switch (opt) {
            case 'i': /* treat stuff controlled by these symbols as text */
                  /*
                   * For strict backwards-compatibility the U or D
                   * should be immediately after the -i but it doesn't
                   * matter much if we relax that requirement.
                   */
                  opt = *optarg++;
                  if (opt == 'D')
                        addsym(true, true, optarg);
                  else if (opt == 'U')
                        addsym(true, false, optarg);
                  else
                        usage();
                  break;
            case 'D': /* define a symbol */
                  addsym(false, true, optarg);
                  break;
            case 'U': /* undef a symbol */
                  addsym(false, false, optarg);
                  break;
            case 'I':
                  /* no-op for compatibility with cpp */
                  break;
            case 'c': /* treat -D as -U and vice versa */
                  complement = true;
                  break;
            case 'd':
                  debugging = true;
                  break;
            case 'e': /* fewer errors from dodgy lines */
                  iocccok = true;
                  break;
            case 'k': /* process constant #ifs */
                  killconsts = true;
                  break;
            case 'l': /* blank deleted lines instead of omitting them */
                  lnblank = true;
                  break;
            case 'n': /* add #line directive after deleted lines */
                  lnnum = true;
                  break;
            case 's': /* only output list of symbols that control #ifs */
                  symlist = true;
                  break;
            case 't': /* don't parse C comments */
                  text = true;
                  break;
            default:
                  usage();
            }
      argc -= optind;
      argv += optind;
      if (argc > 1) {
            errx(2, "can only do one file");
      } else if (argc == 1 && strcmp(*argv, "-") != 0) {
            filename = *argv;
            input = fopen(filename, "r");
            if (input == NULL)
                  err(2, "can't open %s", filename);
      } else {
            filename = "[stdin]";
            input = stdin;
      }
      process();
      abort(); /* bug */
}

static void
usage(void)
{
      fprintf(stderr, "usage: unifdef [-cdeklnst] [-Ipath]"
          " [-Dsym[=val]] [-Usym] [-iDsym[=val]] [-iUsym] ... [file]\n");
      exit(2);
}

/*
 * A state transition function alters the global #if processing state
 * in a particular way. The table below is indexed by the current
 * processing state and the type of the current line.
 *
 * Nesting is handled by keeping a stack of states; some transition
 * functions increase or decrease the depth. They also maintain the
 * ignore state on a stack. In some complicated cases they have to
 * alter the preprocessor directive, as follows.
 *
 * When we have processed a group that starts off with a known-false
 * #if/#elif sequence (which has therefore been deleted) followed by a
 * #elif that we don't understand and therefore must keep, we edit the
 * latter into a #if to keep the nesting correct.
 *
 * When we find a true #elif in a group, the following block will
 * always be kept and the rest of the sequence after the next #elif or
 * #else will be discarded. We edit the #elif into a #else and the
 * following directive to #endif since this has the desired behaviour.
 *
 * "Dodgy" directives are split across multiple lines, the most common
 * example being a multi-line comment hanging off the right of the
 * directive. We can handle them correctly only if there is no change
 * from printing to dropping (or vice versa) caused by that directive.
 * If the directive is the first of a group we have a choice between
 * failing with an error, or passing it through unchanged instead of
 * evaluating it. The latter is not the default to avoid questions from
 * users about unifdef unexpectedly leaving behind preprocessor directives.
 */
typedef void state_fn(void);

/* report an error */
static void Eelif (void) { error("Inappropriate #elif"); }
static void Eelse (void) { error("Inappropriate #else"); }
static void Eendif(void) { error("Inappropriate #endif"); }
static void Eeof  (void) { error("Premature EOF"); }
static void Eioccc(void) { error("Obfuscated preprocessor control line"); }
/* plain line handling */
static void print (void) { flushline(true); }
static void drop  (void) { flushline(false); }
/* output lacks group's start line */
static void Strue (void) { drop();  ignoreoff(); state(IS_TRUE_PREFIX); }
static void Sfalse(void) { drop();  ignoreoff(); state(IS_FALSE_PREFIX); }
static void Selse (void) { drop();               state(IS_TRUE_ELSE); }
/* print/pass this block */
static void Pelif (void) { print(); ignoreoff(); state(IS_PASS_MIDDLE); }
static void Pelse (void) { print();              state(IS_PASS_ELSE); }
static void Pendif(void) { print(); unnest(); }
/* discard this block */
static void Dfalse(void) { drop();  ignoreoff(); state(IS_FALSE_TRAILER); }
static void Delif (void) { drop();  ignoreoff(); state(IS_FALSE_MIDDLE); }
static void Delse (void) { drop();               state(IS_FALSE_ELSE); }
static void Dendif(void) { drop();  unnest(); }
/* first line of group */
static void Fdrop (void) { nest();  Dfalse(); }
static void Fpass (void) { nest();  Pelif(); }
static void Ftrue (void) { nest();  Strue(); }
static void Ffalse(void) { nest();  Sfalse(); }
/* variable pedantry for obfuscated lines */
static void Oiffy (void) { if (!iocccok) Eioccc(); Fpass(); ignoreon(); }
static void Oif   (void) { if (!iocccok) Eioccc(); Fpass(); }
static void Oelif (void) { if (!iocccok) Eioccc(); Pelif(); }
/* ignore comments in this block */
static void Idrop (void) { Fdrop();  ignoreon(); }
static void Itrue (void) { Ftrue();  ignoreon(); }
static void Ifalse(void) { Ffalse(); ignoreon(); }
/* edit this line */
static void Mpass (void) { strncpy(keyword, "if  ", 4); Pelif(); }
static void Mtrue (void) { keywordedit("else\n");  state(IS_TRUE_MIDDLE); }
static void Melif (void) { keywordedit("endif\n"); state(IS_FALSE_TRAILER); }
static void Melse (void) { keywordedit("endif\n"); state(IS_FALSE_ELSE); }

static state_fn * const trans_table[IS_COUNT][LT_COUNT] = {
/* IS_OUTSIDE */
{ Itrue, Ifalse,Fpass, Ftrue, Ffalse,Eelif, Eelif, Eelif, Eelse, Eendif,
  Oiffy, Oiffy, Fpass, Oif,   Oif,   Eelif, Eelif, Eelif, Eelse, Eendif,
  print, done },
/* IS_FALSE_PREFIX */
{ Idrop, Idrop, Fdrop, Fdrop, Fdrop, Mpass, Strue, Sfalse,Selse, Dendif,
  Idrop, Idrop, Fdrop, Fdrop, Fdrop, Mpass, Eioccc,Eioccc,Eioccc,Eioccc,
  drop,  Eeof },
/* IS_TRUE_PREFIX */
{ Itrue, Ifalse,Fpass, Ftrue, Ffalse,Dfalse,Dfalse,Dfalse,Delse, Dendif,
  Oiffy, Oiffy, Fpass, Oif,   Oif,   Eioccc,Eioccc,Eioccc,Eioccc,Eioccc,
  print, Eeof },
/* IS_PASS_MIDDLE */
{ Itrue, Ifalse,Fpass, Ftrue, Ffalse,Pelif, Mtrue, Delif, Pelse, Pendif,
  Oiffy, Oiffy, Fpass, Oif,   Oif,   Pelif, Oelif, Oelif, Pelse, Pendif,
  print, Eeof },
/* IS_FALSE_MIDDLE */
{ Idrop, Idrop, Fdrop, Fdrop, Fdrop, Pelif, Mtrue, Delif, Pelse, Pendif,
  Idrop, Idrop, Fdrop, Fdrop, Fdrop, Eioccc,Eioccc,Eioccc,Eioccc,Eioccc,
  drop,  Eeof },
/* IS_TRUE_MIDDLE */
{ Itrue, Ifalse,Fpass, Ftrue, Ffalse,Melif, Melif, Melif, Melse, Pendif,
  Oiffy, Oiffy, Fpass, Oif,   Oif,   Eioccc,Eioccc,Eioccc,Eioccc,Pendif,
  print, Eeof },
/* IS_PASS_ELSE */
{ Itrue, Ifalse,Fpass, Ftrue, Ffalse,Eelif, Eelif, Eelif, Eelse, Pendif,
  Oiffy, Oiffy, Fpass, Oif,   Oif,   Eelif, Eelif, Eelif, Eelse, Pendif,
  print, Eeof },
/* IS_FALSE_ELSE */
{ Idrop, Idrop, Fdrop, Fdrop, Fdrop, Eelif, Eelif, Eelif, Eelse, Dendif,
  Idrop, Idrop, Fdrop, Fdrop, Fdrop, Eelif, Eelif, Eelif, Eelse, Eioccc,
  drop,  Eeof },
/* IS_TRUE_ELSE */
{ Itrue, Ifalse,Fpass, Ftrue, Ffalse,Eelif, Eelif, Eelif, Eelse, Dendif,
  Oiffy, Oiffy, Fpass, Oif,   Oif,   Eelif, Eelif, Eelif, Eelse, Eioccc,
  print, Eeof },
/* IS_FALSE_TRAILER */
{ Idrop, Idrop, Fdrop, Fdrop, Fdrop, Dfalse,Dfalse,Dfalse,Delse, Dendif,
  Idrop, Idrop, Fdrop, Fdrop, Fdrop, Dfalse,Dfalse,Dfalse,Delse, Eioccc,
  drop,  Eeof }
/*TRUEI  FALSEI IF     TRUE   FALSE  ELIF   ELTRUE ELFALSE ELSE  ENDIF
  TRUEI  FALSEI IF     TRUE   FALSE  ELIF   ELTRUE ELFALSE ELSE  ENDIF (DODGY)
  PLAIN  EOF */
};

/*
 * State machine utility functions
 */
static void
done(void)
{
      if (incomment)
            error("EOF in comment");
      exit(exitstat);
}
static void
ignoreoff(void)
{
      if (depth == 0)
            abort(); /* bug */
      ignoring[depth] = ignoring[depth-1];
}
static void
ignoreon(void)
{
      ignoring[depth] = true;
}
static void
keywordedit(const char *replacement)
{
      size_t size = tline + sizeof(tline) - keyword;
      char *dst = keyword;
      const char *src = replacement;
      if (size != 0) {
            while ((--size != 0) && (*src != '\0'))
                  *dst++ = *src++;
            *dst = '\0';
      }
      print();
}
static void
nest(void)
{
      depth += 1;
      if (depth >= MAXDEPTH)
            error("Too many levels of nesting");
      stifline[depth] = linenum;
}
static void
unnest(void)
{
      if (depth == 0)
            abort(); /* bug */
      depth -= 1;
}
static void
state(Ifstate is)
{
      ifstate[depth] = is;
}

/*
 * Write a line to the output or not, according to command line options.
 */
static void
flushline(bool keep)
{
      if (symlist)
            return;
      if (keep ^ complement) {
            if (lnnum && delcount > 0)
                  printf("#line %d\n", linenum);
            fputs(tline, stdout);
            delcount = 0;
      } else {
            if (lnblank)
                  putc('\n', stdout);
            exitstat = 1;
            delcount += 1;
      }
}

/*
 * The driver for the state machine.
 */
static void
process(void)
{
      Linetype lineval;

      for (;;) {
            linenum++;
            lineval = getline();
            trans_table[ifstate[depth]][lineval]();
            debug("process %s -> %s depth %d",
                linetype_name[lineval],
                ifstate_name[ifstate[depth]], depth);
      }
}

/*
 * Parse a line and determine its type. We keep the preprocessor line
 * parser state between calls in the global variable linestate, with
 * help from skipcomment().
 */
static Linetype
getline(void)
{
      const char *cp;
      int cursym;
      int kwlen;
      Linetype retval;
      Comment_state wascomment;

      if (fgets(tline, MAXLINE, input) == NULL)
            return (LT_EOF);
      retval = LT_PLAIN;
      wascomment = incomment;
      cp = skipcomment(tline);
      if (linestate == LS_START) {
            if (*cp == '#') {
                  linestate = LS_HASH;
                  cp = skipcomment(cp + 1);
            } else if (*cp != '\0')
                  linestate = LS_DIRTY;
      }
      if (!incomment && linestate == LS_HASH) {
            keyword = tline + (cp - tline);
            cp = skipsym(cp);
            kwlen = cp - keyword;
            /* no way can we deal with a continuation inside a keyword */
            if (strncmp(cp, "\\\n", 2) == 0)
                  Eioccc();
            if (strlcmp("ifdef", keyword, kwlen) == 0 ||
                strlcmp("ifndef", keyword, kwlen) == 0) {
                  cp = skipcomment(cp);
                  if ((cursym = findsym(cp)) < 0)
                        retval = LT_IF;
                  else {
                        retval = (keyword[2] == 'n')
                            ? LT_FALSE : LT_TRUE;
                        if (value[cursym] == NULL)
                              retval = (retval == LT_TRUE)
                                  ? LT_FALSE : LT_TRUE;
                        if (ignore[cursym])
                              retval = (retval == LT_TRUE)
                                  ? LT_TRUEI : LT_FALSEI;
                  }
                  cp = skipsym(cp);
            } else if (strlcmp("if", keyword, kwlen) == 0)
                  retval = ifeval(&cp);
            else if (strlcmp("elif", keyword, kwlen) == 0)
                  retval = ifeval(&cp) - LT_IF + LT_ELIF;
            else if (strlcmp("else", keyword, kwlen) == 0)
                  retval = LT_ELSE;
            else if (strlcmp("endif", keyword, kwlen) == 0)
                  retval = LT_ENDIF;
            else {
                  linestate = LS_DIRTY;
                  retval = LT_PLAIN;
            }
            cp = skipcomment(cp);
            if (*cp != '\0') {
                  linestate = LS_DIRTY;
                  if (retval == LT_TRUE || retval == LT_FALSE ||
                      retval == LT_TRUEI || retval == LT_FALSEI)
                        retval = LT_IF;
                  if (retval == LT_ELTRUE || retval == LT_ELFALSE)
                        retval = LT_ELIF;
            }
            if (retval != LT_PLAIN && (wascomment || incomment)) {
                  retval += LT_DODGY;
                  if (incomment)
                        linestate = LS_DIRTY;
            }
            /* skipcomment should have changed the state */
            if (linestate == LS_HASH)
                  abort(); /* bug */
      }
      if (linestate == LS_DIRTY) {
            while (*cp != '\0')
                  cp = skipcomment(cp + 1);
      }
      debug("parser %s comment %s line",
          comment_name[incomment], linestate_name[linestate]);
      return (retval);
}

/*
 * These are the binary operators that are supported by the expression
 * evaluator. Note that if support for division is added then we also
 * need short-circuiting booleans because of divide-by-zero.
 */
static int op_lt(int a, int b) { return (a < b); }
static int op_gt(int a, int b) { return (a > b); }
static int op_le(int a, int b) { return (a <= b); }
static int op_ge(int a, int b) { return (a >= b); }
static int op_eq(int a, int b) { return (a == b); }
static int op_ne(int a, int b) { return (a != b); }
static int op_or(int a, int b) { return (a || b); }
static int op_and(int a, int b) { return (a && b); }

/*
 * An evaluation function takes three arguments, as follows: (1) a pointer to
 * an element of the precedence table which lists the operators at the current
 * level of precedence; (2) a pointer to an integer which will receive the
 * value of the expression; and (3) a pointer to a char* that points to the
 * expression to be evaluated and that is updated to the end of the expression
 * when evaluation is complete. The function returns LT_FALSE if the value of
 * the expression is zero, LT_TRUE if it is non-zero, or LT_IF if the
 * expression could not be evaluated.
 */
struct ops;

typedef Linetype eval_fn(const struct ops *, int *, const char **);

static eval_fn eval_table, eval_unary;

/*
 * The precedence table. Expressions involving binary operators are evaluated
 * in a table-driven way by eval_table. When it evaluates a subexpression it
 * calls the inner function with its first argument pointing to the next
 * element of the table. Innermost expressions have special non-table-driven
 * handling.
 */
static const struct ops {
      eval_fn *inner;
      struct op {
            const char *str;
            int (*fn)(int, int);
      } op[5];
} eval_ops[] = {
      { eval_table, { { "||", op_or } } },
      { eval_table, { { "&&", op_and } } },
      { eval_table, { { "==", op_eq },
                  { "!=", op_ne } } },
      { eval_unary, { { "<=", op_le },
                  { ">=", op_ge },
                  { "<", op_lt },
                  { ">", op_gt } } }
};

/*
 * Function for evaluating the innermost parts of expressions,
 * viz. !expr (expr) defined(symbol) symbol number
 * We reset the keepthis flag when we find a non-constant subexpression.
 */
static Linetype
eval_unary(const struct ops *ops, int *valp, const char **cpp)
{
      const char *cp;
      char *ep;
      int sym;

      cp = skipcomment(*cpp);
      if (*cp == '!') {
            debug("eval%d !", ops - eval_ops);
            cp++;
            if (eval_unary(ops, valp, &cp) == LT_IF)
                  return (LT_IF);
            *valp = !*valp;
      } else if (*cp == '(') {
            cp++;
            debug("eval%d (", ops - eval_ops);
            if (eval_table(eval_ops, valp, &cp) == LT_IF)
                  return (LT_IF);
            cp = skipcomment(cp);
            if (*cp++ != ')')
                  return (LT_IF);
      } else if (isdigit((unsigned char)*cp)) {
            debug("eval%d number", ops - eval_ops);
            *valp = strtol(cp, &ep, 0);
            cp = skipsym(cp);
      } else if (strncmp(cp, "defined", 7) == 0 && endsym(cp[7])) {
            cp = skipcomment(cp+7);
            debug("eval%d defined", ops - eval_ops);
            if (*cp++ != '(')
                  return (LT_IF);
            cp = skipcomment(cp);
            sym = findsym(cp);
            if (sym < 0)
                  return (LT_IF);
            *valp = (value[sym] != NULL);
            cp = skipsym(cp);
            cp = skipcomment(cp);
            if (*cp++ != ')')
                  return (LT_IF);
            keepthis = false;
      } else if (!endsym(*cp)) {
            debug("eval%d symbol", ops - eval_ops);
            sym = findsym(cp);
            if (sym < 0)
                  return (LT_IF);
            if (value[sym] == NULL)
                  *valp = 0;
            else {
                  *valp = strtol(value[sym], &ep, 0);
                  if (*ep != '\0' || ep == value[sym])
                        return (LT_IF);
            }
            cp = skipsym(cp);
            keepthis = false;
      } else {
            debug("eval%d bad expr", ops - eval_ops);
            return (LT_IF);
      }

      *cpp = cp;
      debug("eval%d = %d", ops - eval_ops, *valp);
      return (*valp ? LT_TRUE : LT_FALSE);
}

/*
 * Table-driven evaluation of binary operators.
 */
static Linetype
eval_table(const struct ops *ops, int *valp, const char **cpp)
{
      const struct op *op;
      const char *cp;
      int val;

      debug("eval%d", ops - eval_ops);
      cp = *cpp;
      if (ops->inner(ops+1, valp, &cp) == LT_IF)
            return (LT_IF);
      for (;;) {
            cp = skipcomment(cp);
            for (op = ops->op; op->str != NULL; op++)
                  if (strncmp(cp, op->str, strlen(op->str)) == 0)
                        break;
            if (op->str == NULL)
                  break;
            cp += strlen(op->str);
            debug("eval%d %s", ops - eval_ops, op->str);
            if (ops->inner(ops+1, &val, &cp) == LT_IF)
                  return (LT_IF);
            *valp = op->fn(*valp, val);
      }

      *cpp = cp;
      debug("eval%d = %d", ops - eval_ops, *valp);
      return (*valp ? LT_TRUE : LT_FALSE);
}

/*
 * Evaluate the expression on a #if or #elif line. If we can work out
 * the result we return LT_TRUE or LT_FALSE accordingly, otherwise we
 * return just a generic LT_IF.
 */
static Linetype
ifeval(const char **cpp)
{
      int ret;
      int val;

      debug("eval %s", *cpp);
      keepthis = killconsts ? false : true;
      ret = eval_table(eval_ops, &val, cpp);
      debug("eval = %d", val);
      return (keepthis ? LT_IF : ret);
}

/*
 * Skip over comments, strings, and character literals and stop at the
 * next character position that is not whitespace. Between calls we keep
 * the comment state in the global variable incomment, and we also adjust
 * the global variable linestate when we see a newline.
 * XXX: doesn't cope with the buffer splitting inside a state transition.
 */
static const char *
skipcomment(const char *cp)
{
      if (text || ignoring[depth]) {
            for (; isspace((unsigned char)*cp); cp++)
                  if (*cp == '\n')
                        linestate = LS_START;
            return (cp);
      }
      while (*cp != '\0')
            /* don't reset to LS_START after a line continuation */
            if (strncmp(cp, "\\\n", 2) == 0)
                  cp += 2;
            else switch (incomment) {
            case NO_COMMENT:
                  if (strncmp(cp, "/\\\n", 3) == 0) {
                        incomment = STARTING_COMMENT;
                        cp += 3;
                  } else if (strncmp(cp, "/*", 2) == 0) {
                        incomment = C_COMMENT;
                        cp += 2;
                  } else if (strncmp(cp, "//", 2) == 0) {
                        incomment = CXX_COMMENT;
                        cp += 2;
                  } else if (strncmp(cp, "\'", 1) == 0) {
                        incomment = CHAR_LITERAL;
                        linestate = LS_DIRTY;
                        cp += 1;
                  } else if (strncmp(cp, "\"", 1) == 0) {
                        incomment = STRING_LITERAL;
                        linestate = LS_DIRTY;
                        cp += 1;
                  } else if (strncmp(cp, "\n", 1) == 0) {
                        linestate = LS_START;
                        cp += 1;
                  } else if (strchr(" \t", *cp) != NULL) {
                        cp += 1;
                  } else
                        return (cp);
                  continue;
            case CXX_COMMENT:
                  if (strncmp(cp, "\n", 1) == 0) {
                        incomment = NO_COMMENT;
                        linestate = LS_START;
                  }
                  cp += 1;
                  continue;
            case CHAR_LITERAL:
            case STRING_LITERAL:
                  if ((incomment == CHAR_LITERAL && cp[0] == '\'') ||
                      (incomment == STRING_LITERAL && cp[0] == '\"')) {
                        incomment = NO_COMMENT;
                        cp += 1;
                  } else if (cp[0] == '\\') {
                        if (cp[1] == '\0')
                              cp += 1;
                        else
                              cp += 2;
                  } else if (strncmp(cp, "\n", 1) == 0) {
                        if (incomment == CHAR_LITERAL)
                              error("unterminated char literal");
                        else
                              error("unterminated string literal");
                  } else
                        cp += 1;
                  continue;
            case C_COMMENT:
                  if (strncmp(cp, "*\\\n", 3) == 0) {
                        incomment = FINISHING_COMMENT;
                        cp += 3;
                  } else if (strncmp(cp, "*/", 2) == 0) {
                        incomment = NO_COMMENT;
                        cp += 2;
                  } else
                        cp += 1;
                  continue;
            case STARTING_COMMENT:
                  if (*cp == '*') {
                        incomment = C_COMMENT;
                        cp += 1;
                  } else if (*cp == '/') {
                        incomment = CXX_COMMENT;
                        cp += 1;
                  } else {
                        incomment = NO_COMMENT;
                        linestate = LS_DIRTY;
                  }
                  continue;
            case FINISHING_COMMENT:
                  if (*cp == '/') {
                        incomment = NO_COMMENT;
                        cp += 1;
                  } else
                        incomment = C_COMMENT;
                  continue;
            default:
                  abort(); /* bug */
            }
      return (cp);
}

/*
 * Skip over an identifier.
 */
static const char *
skipsym(const char *cp)
{
      while (!endsym(*cp))
            ++cp;
      return (cp);
}

/*
 * Look for the symbol in the symbol table. If is is found, we return
 * the symbol table index, else we return -1.
 */
static int
findsym(const char *str)
{
      const char *cp;
      int symind;

      cp = skipsym(str);
      if (cp == str)
            return (-1);
      if (symlist) {
            printf("%.*s\n", (int)(cp-str), str);
            /* we don't care about the value of the symbol */
            return (0);
      }
      for (symind = 0; symind < nsyms; ++symind) {
            if (strlcmp(symname[symind], str, cp-str) == 0) {
                  debug("findsym %s %s", symname[symind],
                      value[symind] ? value[symind] : "");
                  return (symind);
            }
      }
      return (-1);
}

/*
 * Add a symbol to the symbol table.
 */
static void
addsym(bool ignorethis, bool definethis, char *sym)
{
      int symind;
      char *val;

      symind = findsym(sym);
      if (symind < 0) {
            if (nsyms >= MAXSYMS)
                  errx(2, "too many symbols");
            symind = nsyms++;
      }
      symname[symind] = sym;
      ignore[symind] = ignorethis;
      val = sym + (skipsym(sym) - sym);
      if (definethis) {
            if (*val == '=') {
                  value[symind] = val+1;
                  *val = '\0';
            } else if (*val == '\0')
                  value[symind] = "";
            else
                  usage();
      } else {
            if (*val != '\0')
                  usage();
            value[symind] = NULL;
      }
}

/*
 * Compare s with n characters of t.
 * The same as strncmp() except that it checks that s[n] == '\0'.
 */
static int
strlcmp(const char *s, const char *t, size_t n)
{
      while (n-- && *t != '\0')
            if (*s != *t)
                  return ((unsigned char)*s - (unsigned char)*t);
            else
                  ++s, ++t;
      return ((unsigned char)*s);
}

/*
 * Diagnostics.
 */
static void
debug(const char *msg, ...)
{
      va_list ap;

      if (debugging) {
            va_start(ap, msg);
            vwarnx(msg, ap);
            va_end(ap);
      }
}

static void
error(const char *msg)
{
      if (depth == 0)
            warnx("%s: %d: %s", filename, linenum, msg);
      else
            warnx("%s: %d: %s (#if line %d depth %d)",
                filename, linenum, msg, stifline[depth], depth);
      errx(2, "output may be truncated");
}

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