A 如果我（早）知道这计算机程序,就能节约大量短时间和精力了
虚拟语气,表示与过去事实相反的情况.其句型为“ if + 主语 + 动词的过去完成式,主语 +would / could / should / might + have + 动词的过去分词”.
这道题里从句Had I known about this computer program是省略了if 然后倒装的=If I had known about this computer program.主句中a huge amount of time and energy和save是被动关系,所以用would have been saved.