Question

int X = a-b;
int d = Math.Abs(X);

I am pretty sure that .NET doesn’t do inlining. So, will I do if(), or is there some other less-known trick?

Answer 1

The JIT performs inlining in some circumstances. I don’t know whether it inlines Math.Abs or not… but have you verified that this is actually a performance problem for you? Don’t micro-optimize until you know that you need to, and then measure the performance gain from something like:

int d = X > 0 ? X : -X;

to verify that it’s really worth it.

As noted by Anthony, the above won’t (normally) work for int.MinValue, as -int.MinValue == int.MinValue, whereas Math.Abs will throw an OverflowException. You can force this in the straight C# as well using checked arithmetic:

int d = X > 0 ? X : checked(-X);