[FFmpeg-devel] [PATCH] avcodec/dxtory: unbreak decoding after 6e1a167c556

Michael Niedermayer michael at niedermayer.cc
Thu Sep 3 23:50:52 EEST 2020


On Thu, Sep 03, 2020 at 07:03:23PM +0200, Paul B Mahol wrote:
> get_unary() takes at minimum only 1 bit.
> 
> Signed-off-by: Paul B Mahol <onemda at gmail.com>
> ---
> 
> As this is important fix, will apply in next 5 minutes.
> I kindly ask authors of various timeouts changes to kindly
> test their changes more carefully.

Can you provide test samples and a fate test ?


> 
> ---
>  libavcodec/dxtory.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/dxtory.c b/libavcodec/dxtory.c
> index bc19f27951..3cd95afe80 100644
> --- a/libavcodec/dxtory.c
> +++ b/libavcodec/dxtory.c
> @@ -395,7 +395,7 @@ static int dx2_decode_slice_5x5(GetBitContext *gb, AVFrame *frame,
>      int stride   = frame->linesize[0];
>      uint8_t *dst = frame->data[0] + stride * line;
>  
> -    for (y = 0; y < left && get_bits_left(gb) > 6 * width; y++) {
> +    for (y = 0; y < left && get_bits_left(gb) >= 3 * width; y++) {
>          for (x = 0; x < width; x++) {
>              b = decode_sym_565(gb, lru[0], 5);
>              g = decode_sym_565(gb, lru[1], is_565 ? 6 : 5);
> @@ -462,7 +462,7 @@ static int dx2_decode_slice_rgb(GetBitContext *gb, AVFrame *frame,
>      int stride   = frame->linesize[0];
>      uint8_t *dst = frame->data[0] + stride * line;
>  
> -    for (y = 0; y < left && get_bits_left(gb) > 6 * width; y++) {
> +    for (y = 0; y < left && get_bits_left(gb) >= 3 * width; y++) {
>          for (x = 0; x < width; x++) {
>              dst[x * 3 + 0] = decode_sym(gb, lru[0]);
>              dst[x * 3 + 1] = decode_sym(gb, lru[1]);

> @@ -508,7 +508,7 @@ static int dx2_decode_slice_410(GetBitContext *gb, AVFrame *frame,
>      uint8_t *U  = frame->data[1] + (ustride >> 2) * line;
>      uint8_t *V  = frame->data[2] + (vstride >> 2) * line;
>  
> -    for (y = 0; y < left - 3 && get_bits_left(gb) > 9 * width; y += 4) {
> +    for (y = 0; y < left - 3 && get_bits_left(gb) >= 4 * width; y += 4) {
>          for (x = 0; x < width; x += 4) {
>              for (j = 0; j < 4; j++)
>                  for (i = 0; i < 4; i++)

iam not sure this is correct
let us consider the equal case occurs get_bits_left(gb) == 4 * width;
now this is read as 4x4 blocks, each will read a minimum of 18 bits 16 luma
and 2 chroma. 18*(width/4) == 4 * width doesnt look right

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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