On Mon, Jun 6, 2011 at 11:57 AM, Benjamin Bellec <b.bel...@gmail.com> wrote: > Le 06/06/2011 17:34, Roland Scheidegger a écrit : >> Am 05.06.2011 03:55, schrieb Benjamin Bellec: >>> Le 05/06/2011 03:05, Matt Turner a écrit : >>>> On Sat, Jun 4, 2011 at 7:14 PM, Benjamin Bellec <b.bel...@gmail.com> wrote: >>>>> Le 03/06/2011 06:09, Matt Turner a écrit : >>>>>> Also, if you want to check if the value is already a power-of-two, >>>>>> instead of a case statement for every POT (including 0), just do the >>>>>> standard is-power-of-two check: >>>>>> >>>>>> (x & (x - 1)) == 0 >>>>> >>>>> My own tests (on a Core2) shows that it's less efficient to do that, at >>>>> least with -O2 optimization enabled. With -O0, it's equal. >>>> >>>> For what input set? Powers of two? >>> Both, my test case loops with 29 POT and 6 NPOT. >>> I'm doing this because the OpenGL games that I have tested call the >>> function more often with "good" values. >>> >>>> >>>> Doesn't really matter, since the function isn't a hot path or >>>> anything, but I'd suppose that the Linux kernel has its >>>> is_power_of_2() function for a reason--that it's pretty ugly to have >>>> lots of case statements like powers of two. >>>> >>>> Matt >>> Ok, so here is a v3 patch which replace the switch statement. >> >> I like this one better too. >> Do we actually need the x == 0 special case or would it be ok if we just >> remove that (which will return 0)? >> >> Roland > > If we delete this check, we need to specify (in a comment) that the > function have an undetermined behavior when passing 0 in parameters. Why > not, but then the most important thing to know is from where the > parameters came from: "mesa" or "GL apps"? If it's from GL apps it could > be dangerous to change the result of this function, even if 0 is a > stupid input (no?).
After a cursory look at the callers, I don't think 0 is ever passed as an argument. But to play it safe I'd probably keep the current behaviour. -Brian _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
