new macro mrb_int(mrb,x) to retrieve mrb_int from mrb_value with conversion if needed

include/mruby.h

@@ -381,6 +381,7 @@ mrb_value mrb_yield_with_class(mrb_state *mrb, mrb_value b, mrb_int argc, const
 
 void mrb_gc_protect(mrb_state *mrb, mrb_value obj);
 mrb_value mrb_to_int(mrb_state *mrb, mrb_value val);
+#define mrb_int(mrb, val) mrb_fixnum(mrb_to_int(mrb, val))
 void mrb_check_type(mrb_state *mrb, mrb_value x, enum mrb_vtype t);
 
 typedef enum call_type {

src/range.c

@@ -242,8 +242,8 @@ range_beg_len(mrb_state *mrb, mrb_value range, mrb_int *begp, mrb_int *lenp, mrb
 
   if (mrb_type(range) != MRB_TT_RANGE) return FALSE;
 
-  beg = b = mrb_fixnum(mrb_to_int(mrb, r->edges->beg));
-  end = e = mrb_fixnum(mrb_to_int(mrb, r->edges->end));
+  beg = b = mrb_int(mrb, r->edges->beg);
+  end = e = mrb_int(mrb, r->edges->end);
 
   if (beg < 0) {
     beg += len;