Factorial algorithm more efficient than naive multiplication

I know how to code for factorials using both iterative and recursive (e.g. n * factorial(n-1) for e.g.). I read in a textbook (without been given any further explanations) that there is an even more efficient way of coding for factorials by dividing them in half recursively. I understand why that may be the case. However I wanted to try coding it on my own, and I don't think I know where to start though. A friend suggested I write base cases first. and I was thinking of using arrays so that I can keep track of the numbers... but I really can't see any way out to designing such a code. What kind of techniques should I be researching?