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Check correctness of types in casting

Not all the casts are valid.

--- a/expr.c

+++ b/expr.c

@@ -38,17 +38,17 @@

 }

 /*

- * Convert the second Node to the type of the first

+ * Convert a Node to a type

  */

 static Node *

-convert(Node *np1, Node *np2)

+convert(Node *np, Type *tp1)

 {

-	Type *tp1, *tp2;

+	Type *tp2;

 	register uint8_t t1, t2;

-	tp1 = UNQUAL(np1->type), tp2 = UNQUAL(np2->type);

+	tp1 = UNQUAL(tp1), tp2 = UNQUAL(np->type);

 	if (tp1 == tp2)

-		return np2;

+		return np;

 	t1 = tp1->op, t2 = tp2->op;

 	switch (t1) {

@@ -55,13 +55,13 @@

 	case ENUM: case INT: case FLOAT:

 		switch (t2) {

 		case INT: case FLOAT: case ENUM:

-			return castcode(np2, tp1);

+			return castcode(np, tp1);

 		}

 		break;

 	case PTR:

 		switch (t2) {

 		case ARY: case FTN:

-			/* TODO: take address of np2 */;

+			/* TODO: take address of np */;

 		}

 	}

 	return NULL;

@@ -302,7 +302,8 @@

 			tp = typename();

 			expect(')');

 			np1 = cast();

-			np2 = castcode(np1, tp);

+			if ((np2 = convert(np2,  tp)) == NULL)

+				error("bad type convertion requested");

 			np2->b.lvalue = np1->b.lvalue;

 			return np1;

 		default:

@@ -487,7 +488,7 @@

 		if (!np1->b.lvalue)

 			goto nolvalue;

 		/* TODO: if it necessary a 0 comparision? */

-		if ((np2 = convert(np1, np2)) == NULL)

+		if ((np2 = convert(np2, np1->type)) == NULL)

 			goto incompatibles;

 		np1 = bincode(op, np1->type, np1, np2);

 	}