Avoid undefined behavior of left shifting negative integer; #3728

src/numeric.c

@@ -962,16 +962,16 @@ lshift(mrb_state *mrb, mrb_int val, mrb_int width)
         (val   > (MRB_INT_MAX >> width))) {
       goto bit_overflow;
     }
+    return mrb_fixnum_value(val << width);
   }
   else {
     if ((width > NUMERIC_SHIFT_WIDTH_MAX) ||
         (val   < (MRB_INT_MIN >> width))) {
       goto bit_overflow;
     }
+    return mrb_fixnum_value(val * (1u << width));
   }
 
-  return mrb_fixnum_value(val << width);
-
 bit_overflow:
   {
     mrb_float f = (mrb_float)val;