Hi Andreas, First off all, thanks for having a look! :)
On Tue, Feb 27, 2024 at 1:37 PM Andreas Rheinhardt <andreas.rheinha...@outlook.com> wrote: > > Sean McGovern: > > --- > > libavcodec/aacenc_pred.c | 4 +++- > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/libavcodec/aacenc_pred.c b/libavcodec/aacenc_pred.c > > index f87fcd5a00..d3efade85e 100644 > > --- a/libavcodec/aacenc_pred.c > > +++ b/libavcodec/aacenc_pred.c > > @@ -162,9 +162,11 @@ void ff_aac_adjust_common_pred(AACEncContext *s, > > ChannelElement *cpe) > > sce1->ics.window_sequence[0] == EIGHT_SHORT_SEQUENCE) > > return; > > > > + const int num_swb = FFMIN(sce0->ics.num_swb, > > sizeof(sce0->ics.prediction_used)); > > + > > for (w = 0; w < sce0->ics.num_windows; w += sce0->ics.group_len[w]) { > > start = 0; > > - for (g = 0; g < sce0->ics.num_swb; g++) { > > + for (g = 0; g < num_swb; g++) { > > int sfb = w*16+g; > > int sum = sce0->ics.prediction_used[sfb] + > > sce1->ics.prediction_used[sfb]; > > float ener0 = 0.0f, ener1 = 0.0f, ener01 = 0.0f; > > As you can see, the actual index used for accesses is w*16 + g and not > only g. So I was surprised that your fix fixed the test (as you claim). > Digging into the code, num_windows can be either 1 or eight and it is > only eight if window_sequence[0] is EIGHT_SHORT_SEQUENCE (see lines > 477-488 in aacpsy.c as well as lines 877-897 in aacenc.c). In case > window_sequence[0] is EIGHT_SHORT_SEQUENCE, we do not even enter this > loop in ff_aac_adjust_common_pred(). This means that the outer loop > above is actually not a loop at all and your fix would indeed fix the > undefined behaviour. > But this also shows that this whole code is a mess. Someone who actually > knows it should take a look. Or maybe the grim reaper. > Anyway, your fix would lead to a wdeclaration-after-statement warning. > Ooof, OK thanks. I was wondering about that when I looked on Patchwork. Thanks, -- Sean McGovern _______________________________________________ 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".