t := stats.TotalAlloc
	f()
	runtime.ReadMemStats(&stats)
	return stats.TotalAlloc - t
}

// TestMulUnbalanced tests that multiplying numbers of different lengths
// does not cause deep recursion and in turn allocate too much memory.
// Test case for issue 3807.
func TestMulUnbalanced(t *testing.T) {
	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(1))
	x := rndNat(50000)
	y := rndNat(40)