Division by two is very simple and clear to code, that's something.
This, it's easy precise code..
I really don't think the halving block reward in December will be very disruptive. All parties know A) that it will happen and B) when it will happen. Markets are very good at pricing in information that's widely known. It might cause a little volatility in one way or another, but it will be temporary and highly manageable.
Precisely, because the information is completely public and available to everyone game theory suggest the market will price the reduction in before it will actually happen and the change wont be disruptive at all.