// we can add p and still be within 32 bytes.
		x, _ = new(big.Int).SetString("31931927535157963707678568152204072984517581467226068221761862915403492091210", 10)
		y, _ = new(big.Int).SetString("5208467867388784005506817585327037698770365050895731383201516607147", 10)
		y.Add(y, p)

		if p.Cmp(y) > 0 || y.BitLen() != 256 {
			t.Fatal("y not within expected range")
		}

		// marshal
		x.FillBytes(invalid[1 : 1+byteLen])