On Thu, 2015-12-17 at 19:22 +0100, Michael Niedermayer wrote: > On Thu, Dec 17, 2015 at 05:29:58PM +0000, Rostislav Pehlivanov wrote: > > This commit adds a raw integer log2 function (which directly maps > > to a > > builtin). This was needed as the Daala entropy coding system > > requires a > > raw log2 and the existing ff_log2 OR'd the argument with 1. > > __builtin_clz(0) is undefined as ganesh pointed out elsewhere > > if i read the intend correctly though this function is added because > of different behavior for 0, but IIUC its not different in a good w
No, this function is added because the OR'd argument in the current ff_log2(x) completely breaks the entropy decoding system because for example, (32|1)!=32. The entropy decoding system doesn't depend on any undefined behavior which occurs when the argument is 0 and in fact would assert should this happen. I don't think that in this case it's the job of the macro/alias to check for whether the argument is 0, but rather it would be the responsibility of anyone using it so they could instead decide what happens rather than silently get the wrong value. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
