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Add ifdef and ifndef clauses

This is a first versin, but it is functional. There is some points that are
not very elegant, but they can be solved later.

--- a/cc1/cc1.h

+++ b/cc1/cc1.h

@@ -266,6 +266,7 @@

 /* lex.c */

 extern char ahead(void);

 extern unsigned next(void);

+extern bool moreinput(void);

 extern void expect(unsigned tok);

 extern void discard(void);

 extern char *getfname(void);

--- a/cc1/cpp.c

+++ b/cc1/cpp.c

@@ -13,6 +13,7 @@

 static char *argp;

 static unsigned arglen;

+static unsigned numif;

 static Symbol *lastmacro;

 static void

@@ -266,7 +267,6 @@

 static char *

 define(char *s)

 {

-	extern char yytext[];

 	char *t;

 	size_t len;

 	Symbol *sym;

@@ -391,6 +391,59 @@

 	exit(-1);

 }

+static char *

+ifclause(char *s, int isdef)

+{

+	unsigned curif, len;

+	char *endp;

+	Symbol *sym;

+

+

+	while (isspace(*s))

+		++s;

+	for (endp = s; isalnum(*endp) || *endp == '_'; ++endp)

+		/* nothing */;

+	if ((len = endp - s) > IDENTSIZ)

+		error("...");

+	memcpy(yytext, s, len);

+	yytext[len] = '\0';

+	while (isspace(*endp))

+		++endp;

+	if (*endp != '\0')

+		error("trailing characters after preprocessor directive");

+

+	curif = numif++;

+	sym = lookup(NS_CPP);

+	if ((sym->flags & ISDEFINED) != 0 == isdef)

+		return endp;

+	while (curif != numif) {

+		if (!moreinput())

+			error("found EOF while ...");

+	}

+	return "";

+}

+

+static char *

+ifdef(char *s)

+{

+	return ifclause(s, 1);

+}

+

+static char *

+ifndef(char *s)

+{

+	return ifclause(s, 0);

+}

+

+static char *

+endif(char *s)

+{

+	if (numif == 0)

+		error("#endif without #if");

+	--numif;

+	return NULL;

+}

+

 char *

 preprocessor(char *p)

 {

@@ -402,6 +455,9 @@

 	} *bp, cmds[] =  {

 		"define", define,

 		"include", include,

+		"ifdef", ifdef,

+		"ifndef", ifndef,

+		"endif", endif,

 		"line", line,

 		"pragma", pragma,

 		"error", usererr,

@@ -425,9 +481,10 @@

 	for (bp = cmds; bp->name; ++bp) {

 		if (strncmp(bp->name, p, n))

 			continue;

-		q = (*bp->fun)(q);

-		while (isspace(*q++))

-			/* nothing */;

+		if ((q = (*bp->fun)(q)) == NULL)

+			return NULL;

+		while (isspace(*q))

+			++q;

 		if (*q != '\0')

 			error("trailing characters after preprocessor directive");

 		return q;

--- a/cc1/lex.c

+++ b/cc1/lex.c

@@ -186,7 +186,7 @@

 	*bp = '\0';

 }

-static bool

+bool

 moreinput(void)

 {

 	char *p;

@@ -202,7 +202,9 @@

 	*(p = input->line) = '\0';

 	readline();

-	if (*(p = preprocessor(p)) == '\0')

+	if ((p = preprocessor(p)) == NULL)

+		return 1;

+	if (*p == '\0')

 		goto repeat;

 	input->p = input->begin = p;

 	return 1;