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Reducing scope of variables in asign

This helps to the compiler in order to generate a good code.

--- a/expr.c

+++ b/expr.c

@@ -298,28 +298,29 @@

 static struct node *

 assign(void)

 {

-	register unsigned char op;

-	register struct node *np;

+	register struct node *np = cond();

-	np = cond();

 	for (;;) {

+		register unsigned char op;

+

 		switch (yytoken) {

-		case '=': op = OASSIGN; break;

-		case MUL_EQ: op = OA_MUL; break;

-		case DIV_EQ: op = OA_DIV; break;

-		case MOD_EQ: op = OA_MOD; break;

-		case ADD_EQ: op = OA_ADD; break;

-		case SUB_EQ: op = OA_SUB; break;

-		case SHL_EQ: op = OA_SHL; break;

-		case SHR_EQ: op = OA_SHR; break;

-		case AND_EQ: op = OA_AND; break;

-		case XOR_EQ: op = OA_XOR; break;

-		case OR_EQ: op = OA_OR; break;

-		default: return np;

+		case '=':    op = OASSIGN; break;

+		case MUL_EQ: op = OA_MUL;  break;

+		case DIV_EQ: op = OA_DIV;  break;

+		case MOD_EQ: op = OA_MOD;  break;

+		case ADD_EQ: op = OA_ADD;  break;

+		case SUB_EQ: op = OA_SUB;  break;

+		case SHL_EQ: op = OA_SHL;  break;

+		case SHR_EQ: op = OA_SHR;  break;

+		case AND_EQ: op = OA_AND;  break;

+		case XOR_EQ: op = OA_XOR;  break;

+		case OR_EQ:  op = OA_OR;   break;

+		default:  goto return_np;

 		}

 		next();

 		np = node2(op, np, assign());

 	}

+return_np:

 	return np;

 }