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. - Andreas