I read a sentence in a dialogue script. A man was explaining to his lawyer why he punched a stranger (because the stranger was harassing the man's girlfriend). In the dialogue, the man said: "If I hadn't have done that, who knows what he may have done to my girlfriend." I think this is a subjunctive sentence, because he was saying something that was the opposite of what happened (as he did punch the stranger). But my question is, why did he use "If I hadn't have done" here? I thought for past subjunctive, you say "If I had done..., I would have done..." So why it's "If I hadn't have done" instead of "If I hadn't done" here? Is there any difference between the two expressions? Thank you in advance for your help!