/*
 * Copyright (c) 2002 - 2009 Tony Finch <dot@dotat.at>
 *
 * 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.
 */

/*
 * This code was 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 4-clause BSD copyright licence. None of its code
 * remains in this version (though some of the names remain) so it now
 * carries a more liberal licence.
 *
 * The latest version is available from http://dotat.at/prog/unifdef
 */

static const char * const copyright[] = {
    "@(#) Copyright (c) 2002 - 2009 Tony Finch <dot@dotat.at>\n",
    "$dotat: unifdef/unifdef.c,v 1.190 2009/11/27 17:21:26 fanf2 Exp $",
};

/*
 * 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>

/* 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_ERROR,               /* unevaluable #if */
        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", "ERROR"
};

/* 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             compblank;              /* -B: compress blank lines */
static bool             lnblank;                /* -b: blank deleted lines */
static bool             complement;             /* -c: do the complement */
static bool             debugging;              /* -d: debugging reports */
static bool             iocccok;                /* -e: fewer IOCCC errors */
static bool             strictlogic;            /* -K: keep ambiguous #ifs */
static bool             killconsts;             /* -k: eval constant #ifs */
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 unsigned         blankcount;             /* count of blank lines */
static unsigned         blankmax;               /* maximum recent blankcount */
static bool             constexpr;              /* constant #if expression */

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         parseline(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      *skipargs(const char *);
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) (!isalnum((unsigned char)c) && c != '_')

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

        while ((opt = getopt(argc, argv, "i:D:U:I:BbcdeKklnst")) != -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 'B': /* compress blank lines around removed section */
                        compblank = true;
                        break;
                case 'b': /* blank deleted lines instead of omitting them */
                case 'l': /* backwards compatibility */
                        lnblank = true;
                        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': /* keep ambiguous #ifs */
                        strictlogic = true;
                        break;
                case 'k': /* process constant #ifs */
                        killconsts = 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 (compblank && lnblank)
                errx(2, "-B and -b are mutually exclusive");
        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 [-BbcdeKknst] [-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,  abort },
/* 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,  abort },
/* 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,  abort },
/* 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,  abort },
/* 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,  abort },
/* 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,  abort },
/* 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,  abort },
/* 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,  abort },
/* 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,  abort },
/* 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,  abort }
/*TRUEI  FALSEI IF     TRUE   FALSE  ELIF   ELTRUE ELFALSE ELSE  ENDIF
  TRUEI  FALSEI IF     TRUE   FALSE  ELIF   ELTRUE ELFALSE ELSE  ENDIF (DODGY)
  PLAIN  EOF    ERROR */
};

/*
 * 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)
{
        if (depth > MAXDEPTH-1)
                abort(); /* bug */
        if (depth == MAXDEPTH-1)
                error("Too many levels of nesting");
        depth += 1;
        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) {
                bool blankline = tline[strspn(tline, " \t\n")] == '\0';
                if (blankline && compblank && blankcount != blankmax) {
                        delcount += 1;
                        blankcount += 1;
                } else {
                        if (lnnum && delcount > 0)
                                printf("#line %d\n", linenum);
                        fputs(tline, stdout);
                        delcount = 0;
                        blankmax = blankcount = blankline ? blankcount + 1 : 0;
                }
        } else {
                if (lnblank)
                        putc('\n', stdout);
                exitstat = 1;
                delcount += 1;
                blankcount = 0;
        }
}

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

        /* When compressing blank lines, act as if the file
           is preceded by a large number of blank lines. */
        blankmax = blankcount = 1000;
        for (;;) {
                linenum++;
                lineval = parseline();
                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
parseline(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 normally changes the state, except
                   if the last line of the file lacks a newline, or
                   if there is too much whitespace in a directive */
                if (linestate == LS_HASH) {
                        size_t len = cp - tline;
                        if (fgets(tline + len, MAXLINE - len, input) == NULL) {
                                /* append the missing newline */
                                tline[len+0] = '\n';
                                tline[len+1] = '\0';
                                cp++;
                                linestate = LS_START;
                        } else {
                                linestate = LS_DIRTY;
                        }
                }
        }
        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.
 */
static Linetype op_strict(int *p, int v, Linetype at, Linetype bt) {
        if(at == LT_IF || bt == LT_IF) return (LT_IF);
        return (*p = v, v ? LT_TRUE : LT_FALSE);
}
static Linetype op_lt(int *p, Linetype at, int a, Linetype bt, int b) {
        return op_strict(p, a < b, at, bt);
}
static Linetype op_gt(int *p, Linetype at, int a, Linetype bt, int b) {
        return op_strict(p, a > b, at, bt);
}
static Linetype op_le(int *p, Linetype at, int a, Linetype bt, int b) {
        return op_strict(p, a <= b, at, bt);
}
static Linetype op_ge(int *p, Linetype at, int a, Linetype bt, int b) {
        return op_strict(p, a >= b, at, bt);
}
static Linetype op_eq(int *p, Linetype at, int a, Linetype bt, int b) {
        return op_strict(p, a == b, at, bt);
}
static Linetype op_ne(int *p, Linetype at, int a, Linetype bt, int b) {
        return op_strict(p, a != b, at, bt);
}
static Linetype op_or(int *p, Linetype at, int a, Linetype bt, int b) {
        if (!strictlogic && (at == LT_TRUE || bt == LT_TRUE))
                return (*p = 1, LT_TRUE);
        return op_strict(p, a || b, at, bt);
}
static Linetype op_and(int *p, Linetype at, int a, Linetype bt, int b) {
        if (!strictlogic && (at == LT_FALSE || bt == LT_FALSE))
                return (*p = 0, LT_FALSE);
        return op_strict(p, a && b, at, bt);
}

/*
 * 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, LT_IF if the expression
 * depends on an unknown symbol, or LT_ERROR if there is a parse failure.
 */
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;
                Linetype (*fn)(int *, Linetype, int, Linetype, 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) number defined(symbol) symbol
 * We reset the constexpr flag in the last two cases.
 */
static Linetype
eval_unary(const struct ops *ops, int *valp, const char **cpp)
{
        const char *cp;
        char *ep;
        int sym;
        bool defparen;
        Linetype lt;

        cp = skipcomment(*cpp);
        if (*cp == '!') {
                debug("eval%d !", ops - eval_ops);
                cp++;
                lt = eval_unary(ops, valp, &cp);
                if (lt == LT_ERROR)
                        return (LT_ERROR);
                if (lt != LT_IF) {
                        *valp = !*valp;
                        lt = *valp ? LT_TRUE : LT_FALSE;
                }
        } else if (*cp == '(') {
                cp++;
                debug("eval%d (", ops - eval_ops);
                lt = eval_table(eval_ops, valp, &cp);
                if (lt == LT_ERROR)
                        return (LT_ERROR);
                cp = skipcomment(cp);
                if (*cp++ != ')')
                        return (LT_ERROR);
        } else if (isdigit((unsigned char)*cp)) {
                debug("eval%d number", ops - eval_ops);
                *valp = strtol(cp, &ep, 0);
                if (ep == cp)
                        return (LT_ERROR);
                lt = *valp ? LT_TRUE : LT_FALSE;
                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 == '(') {
                        cp = skipcomment(cp+1);
                        defparen = true;
                } else {
                        defparen = false;
                }
                sym = findsym(cp);
                if (sym < 0) {
                        lt = LT_IF;
                } else {
                        *valp = (value[sym] != NULL);
                        lt = *valp ? LT_TRUE : LT_FALSE;
                }
                cp = skipsym(cp);
                cp = skipcomment(cp);
                if (defparen && *cp++ != ')')
                        return (LT_ERROR);
                constexpr = false;
        } else if (!endsym(*cp)) {
                debug("eval%d symbol", ops - eval_ops);
                sym = findsym(cp);
                cp = skipsym(cp);
                if (sym < 0) {
                        lt = LT_IF;
                        cp = skipargs(cp);
                } else if (value[sym] == NULL) {
                        *valp = 0;
                        lt = LT_FALSE;
                } else {
                        *valp = strtol(value[sym], &ep, 0);
                        if (*ep != '\0' || ep == value[sym])
                                return (LT_ERROR);
                        lt = *valp ? LT_TRUE : LT_FALSE;
                        cp = skipargs(cp);
                }
                constexpr = false;
        } else {
                debug("eval%d bad expr", ops - eval_ops);
                return (LT_ERROR);
        }

        *cpp = cp;
        debug("eval%d = %d", ops - eval_ops, *valp);
        return (lt);
}

/*
 * 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;
        Linetype lt, rt;

        debug("eval%d", ops - eval_ops);
        cp = *cpp;
        lt = ops->inner(ops+1, valp, &cp);
        if (lt == LT_ERROR)
                return (LT_ERROR);
        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);
                rt = ops->inner(ops+1, &val, &cp);
                if (rt == LT_ERROR)
                        return (LT_ERROR);
                lt = op->fn(valp, lt, *valp, rt, val);
        }

        *cpp = cp;
        debug("eval%d = %d", ops - eval_ops, *valp);
        debug("eval%d lt = %s", ops - eval_ops, linetype_name[lt]);
        return (lt);
}

/*
 * 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 = 0;

        debug("eval %s", *cpp);
        constexpr = killconsts ? false : true;
        ret = eval_table(eval_ops, &val, cpp);
        debug("eval = %d", val);
        return (constexpr ? LT_IF : ret == LT_ERROR ? 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 macro arguments.
 */
static const char *
skipargs(const char *cp)
{
        const char *ocp = cp;
        int level = 0;
        cp = skipcomment(cp);
        if (*cp != '(')
                return (cp);
        do {
                if (*cp == '(')
                        level++;
                if (*cp == ')')
                        level--;
                cp = skipcomment(cp+1);
        } while (level != 0 && *cp != '\0');
        if (level == 0)
                return (cp);
        else
        /* Rewind and re-detect the syntax error later. */
                return (ocp);
}

/*
 * 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 it 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");
}