Actually, it was written by Piers Anthony. I know, I was dumbfounded when I found out but I actually read the book, it just so happened at the time I was devouring Piers' vast catalog intensively. He also wrote some other stuff that was outside his normal teenage boy scifi/fantasy hybrid but I forget what it was just now.

Ok, to be precise, Dick did invent the original concept, but Anthony wrote what was made into a movie. http://www.goodreads.com/book/show/15512.Total_Recall