On Tue, 16 Jun 2009, Guennadi Liakhovetski wrote: > > 01/14: compat: handle __fls > > http://linuxtv.org/hg/~tap/v4l-dvb?cmd=changeset;node=c4b55ce6c273 > > > > 02/14: v4l2: Create helper function for bounding and aligning images > > http://linuxtv.org/hg/~tap/v4l-dvb?cmd=changeset;node=b4d3ec8d363d > > I am sorry, I will not bother with saving, reformatting, pasting... Just > wanted to ask about this place: I guess you do not use Mercurial like all other v4l-dvb developers? Because you are making a big deal about a simple operation than can be done with a few keystrokes. If I wanted this patch quoted in my editor, I can simply type: !!cd ~/v4l-dvb ; hg export b4d3ec8d363d | sed 's/^/> /' That is less then you wrote to complain how about how hard this is for you. > + if (walign + halign < salign) { > + /* Max walign where there is still a valid width */ > + unsigned int wmaxa = __fls(wmax ^ (wmin - 1)); > > I cannot follow correctness of the above, sorry. Take a simple example: > wmax=0x7f, wmin=7, wmaxa = __fls(0x7f ^ 6) = __fls(0x79) = 0. And the > comment says it's the "maximum walign where there is still a valid width." > What am I missing? What you are missing is __fls vs __ffs. __fls() finds the _last_ set bit. In this case __fls(0x79) = 6. Which is correct as 1 << 6 = 0x40, and there is a multiple of 0x40 between 0x7f and 7, while there are no multiples of the next higher alignment, 0x80, between 0x7f and 7. In a more difficult example, wmax=0x7f and wmin=0x71, the largest alignment possible is 1 << 3 == 0x08. The next higher alignment, 0x10, will not work as 0x70 is too small and 0x80 is too large. __fls(0x7f ^ 0x70) = __fls(0x0f) = 3. > + > + /* up the smaller alignment until we have enough */ > + do { > + if (walign <= halign && walign < wmaxa) { Thank you for bringing this code up again, as I now realize there is a bug here. It doesn't check if halign is below hmaxa, or even calculate hmaxa. I thought this would be ok because the code isn't designed to handle impossible constraints. But it might increase halign too much when it's possible to satisfy the salign requirement by increasing walign. -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
