Paul B Mahol: > On Tue, Jun 27, 2023 at 11:45 PM Andreas Rheinhardt < > andreas.rheinha...@outlook.com> wrote: > >> Paul B Mahol: >>> On Tue, Jun 27, 2023 at 11:05 PM Andreas Rheinhardt < >>> andreas.rheinha...@outlook.com> wrote: >>> >>>> Paul B Mahol: >>>>> On Tue, Jun 27, 2023 at 9:47 PM Andreas Rheinhardt < >>>>> andreas.rheinha...@outlook.com> wrote: >>>>> >>>>>> Paul B Mahol: >>>>>>> Patch attached. >>>>>>> >>>>>> >>>>>> Where do you intend to use this? What is the point of it? >>>>>> After all, using this value in GET_VLC makes no sense; only >> compile-time >>>>>> constants do. >>>>>> >>>>> >>>>> It works when used in ac-4 as get_vlc2. >>>>> >>>> >>>> Could you please define "works"? Using a non-compile-time constant will >>>> not benefit at all; it will only lead to more runtime checks. >>>> >>> >>> I do not follow your worries. >>> I can not use compile time constant as its very complicated code. >>> >> >> Let's take a look at GET_VLC: >> #define GET_VLC(code, name, gb, table, bits, max_depth) \ >> do { \ >> int n, nb_bits; \ >> unsigned int index; \ >> \ >> index = SHOW_UBITS(name, gb, bits); \ >> code = table[index].sym; \ >> n = table[index].len; \ >> \ >> if (max_depth > 1 && n < 0) { \ >> LAST_SKIP_BITS(name, gb, bits); \ >> UPDATE_CACHE(name, gb); \ >> \ >> nb_bits = -n; \ >> \ >> index = SHOW_UBITS(name, gb, nb_bits) + code; \ >> code = table[index].sym; \ >> n = table[index].len; \ >> if (max_depth > 2 && n < 0) { \ >> LAST_SKIP_BITS(name, gb, nb_bits); \ >> UPDATE_CACHE(name, gb); \ >> \ >> nb_bits = -n; \ >> \ >> index = SHOW_UBITS(name, gb, nb_bits) + code; \ >> code = table[index].sym; \ >> n = table[index].len; \ >> } \ >> } \ >> SKIP_BITS(name, gb, n); \ >> } while (0) >> >> If max_depth is not a compile-time constant, then the compiler will have >> to perform both of the max_depth > 1 && n < 0 checks; yet, this is not >> useful: If the depth of a particular VLC is (say) 1, then none of the >> possible bits read will lead to reloading at all, because the n < 0 >> condition will never be true; the only reason this condition exists is >> to use a compile-time upper bound, so that one can eliminate the reload >> code (and in particular, avoid the runtime checks). >> >>> Works means that vlc code is extracted correctly. >>> >> >> If you have no upper bound about max_depth and it works, then use 3. >> > > It does not work to use 3 all the time. And that one never worked in any > codec so far. >
I just ran FATE with the check for max_depth removed from GET_VLC and from read_vlc for the cached API (effectively setting max_depth to 3 everywhere). It passed. So it "works" (but in a suboptimal way). At least it does if you have ordinary VLCs (created by the vlc.c functions). Are you doing anything special with them or so? - Andreas _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".