Arithmetic type emulator helper class for testcases.

[Paolo Carlini]

Hi Chris,

> Since I need it in several test case files, can it be placed
> in one of the util headers? Does it seem like something useful outside
> of duration testing?

The idea certainly makes sense. Many time in the past set of testcases for new facilities included some infrastructure like that. I think you should just make sure the code follows the existing practice for the general features and just submit it with the rest. Can you remind me where are we as regards <chrono>? Do we need some configury bits to enable the code only when some system calls are available or something like that?

Paolo.