Challenge of the Week (Month?)

Here’s a nice challenge question I got from a very ingenious developer working at Microsoft… now that I’ve found the solution, I thought I should ask it out in the open.

Correct, complete and full answer gets you a nice prize [ie: your name and solution published ;)].

Find the fastest (total cycles) and smallest (total size) method of obtaining the current CPU number that current thread is executing on, on a Windows 2003 or higher computer (ie: this solution can take advantage of any API or system improvements added to NT 5.2+).

  1. You may use an API call if you wish, but be aware that the actual call and stack operations will count in your total.
  2. You may duplicate the contents of an API call, but be aware that you must explain what your code does in detail. Inlining an API you understand nothing about is not a complete solution.
  3. Code must work from user-mode. You can write a kernel driver or user a native function, but the total cycles spend on the ring transition will be factored in your total, plus any size of code spent in kernel-mode.

Email solutions to aionescu at gmail dot com. Posts questions in the comments if you have any.

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