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Add case statement

This version of case is a first version, where there are some
checks that are not done (for example type of the expression),
but is good enough for us now.

--- a/stmt.c

+++ b/stmt.c

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

 #include "cc1.h"

 struct scase {

-	int val;

 	Symbol *label;

 	Node *expr;

 	struct scase *next;

@@ -223,8 +222,33 @@

 	if (lcase.deflabel)

 		emitdefault(lcase.deflabel);

 	emitlabel(lbreak);

+	/* TODO: free memory */

 }

+static void

+Case(Symbol *lbreak, Symbol *lcont, Caselist *lswitch)

+{

+	Node *np;

+	Symbol *lcase = label(NULL, 1);

+	struct scase *pcase;

+

+	if (!lswitch)

+		error("case label not within a switch statement");

+	expect(CASE);

+	if (yytoken == ':')

+		error("expected expression before ':'");

+	np = eval(expr());

+	/* TODO: check integer type */

+	expect(':');

+	emitlabel(lcase);

+	pcase = xmalloc(sizeof(*pcase));

+	pcase->expr = np;

+	pcase->label = lcase;

+	pcase->next = lswitch->head;

+	lswitch->head = pcase;

+	++lswitch->nr;

+}

+

 void

 compound(Symbol *lbreak, Symbol *lcont, Caselist *lswitch)

 {

@@ -258,6 +282,7 @@

 	case CONTINUE: Continue(lcont); break;

 	case GOTO:     Goto(); break;

 	case SWITCH:   Switch(lcont); break;

+	case CASE:     Case(lbreak, lcont, lswitch); break;

 	case IDEN:

 		if (ahead() == ':') {

 			Label();