[Bug #19476]: correct cache index computation for repetition (#7457)

regexec.c

@@ -1248,10 +1248,10 @@ find_cache_index_table(regex_t* reg, OnigStackType *stk, OnigStackIndex *repeat_
   }
 
   if (range->upper == 0x7fffffff) {
-    return range->base_num + range->inner_num * range->lower + (is_inc ? 0 : 1) + item->num;
+    return range->base_num + range->inner_num * (range->lower - (is_inc ? 1 : 0)) + (is_inc ? 0 : 1) + item->num;
   }
 
-  return range->base_num + range->inner_num * range->lower + (range->inner_num + 1) * (count - range->lower) + item->num;
+  return range->base_num + range->inner_num * (range->lower - 1) + (range->inner_num + 1) * (count - range->lower + 1) + item->num;
 }
 
 static void

test/ruby/test_regexp.rb

@@ -1765,6 +1765,11 @@ class TestRegexp < Test::Unit::TestCase
     end;
   end
 
+  def test_bug_19476 # [Bug #19476]
+    assert_equal("123456789".match(/(?:x?\dx?){2,10}/)[0], "123456789")
+    assert_equal("123456789".match(/(?:x?\dx?){2,}/)[0], "123456789")
+  end
+
   def test_linear_time_p
     assert_send [Regexp, :linear_time?, /a/]
     assert_send [Regexp, :linear_time?, 'a']