diff --git a/scripts/unifdef.c b/scripts/unifdef.c
new file mode 100644
index 0000000..5384b43
--- /dev/null
+++ b/scripts/unifdef.c
@@ -0,0 +1,998 @@
+/*
+ * 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)
+{
+	strlcpy(keyword, replacement, tline + sizeof(tline) - keyword);
+	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");
+}