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 _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
