请教Prep上一个句子的解读

windyzhong

其实是CR题(Prep-2-45)，但是句子没读懂，所以拿上来请教大家：

        

The recent decline in the value of the dollar was
triggered by a prediction of slower economic growth in the coming year.  But that prediction would not have adversely affected the
dollar had it not been for the government's huge budget deficit（这句话的结构如何解啊？）,
which must therefore be decreased to prevent future currency declines.

请问绿色部分的had it not been...是什么结构呢？这句话要怎么理解？谢谢！

        
    

AlienX

But that prediction would not have adversely affected the dollar had it not been for the government's huge budget deficit=
But that prediction would not have adversely affected the dollar if it had not been for the government's huge budget deficit