Re: [FFmpeg-devel] [PATCH v1 2/3] avcodec/jpeg2000dec: add support for HTJ2K block decoding

[Pierre-Anthony Lemieux <pal@sandflow.com>]

On Sun, Apr 2, 2023 at 3:17 PM Michael Niedermayer
<michael@niedermayer.cc> wrote:
>
> On Fri, Mar 31, 2023 at 08:29:40AM -0700, pal@sandflow.com wrote:
> > From: caleb <etemesicaleb@gmail.com>
> [...]
> > @@ -1113,8 +1117,29 @@ static int jpeg2000_decode_packet(Jpeg2000DecoderContext *s, Jpeg2000Tile *tile,
> >                      }
> >                  }
> >
> > -                if ((ret = get_bits(s, av_log2(newpasses1) + cblk->lblock)) < 0)
> > -                    return ret;
> > +                if (newpasses > 1 && s->is_htj2k) {
> > +                    // Retrieve pass lengths for each pass
> > +                    int href_passes =  (cblk->npasses + newpasses - 1) % 3;
> > +                    int segment_passes = newpasses - href_passes;
> > +                    int pass_bound = 2;
> > +                    int eb = 0;
> > +                    int extra_bit = newpasses > 2 ? 1 : 0;
> > +                    while (pass_bound <=segment_passes) {
> > +                        eb++;
> > +                        pass_bound +=pass_bound;
> > +                    }
>
> something with av_log2() should be able to do this simpler
>
>
> [...]
> > +/**
> > + * Drops bits from lower bits in the bit buffer. buf contains the bit buffers.
> > + * nbits is the number of bits to remove.
> > + */
> > +av_always_inline
> > +static void jpeg2000_bitbuf_drop_bits_lsb(StateVars *buf, uint8_t nbits)
> > +{
> > +    if (buf->bits_left < nbits) {
>
> > +        av_log(NULL, AV_LOG_ERROR, "Invalid bit read of %d, bits in buffer are %d\n", nbits, buf->bits_left);
> > +        av_assert0(0);
>
>
> [...]
> > +int
> > +ff_jpeg2000_decode_htj2k(const Jpeg2000DecoderContext *s, Jpeg2000CodingStyle *codsty, Jpeg2000T1Context *t1, Jpeg2000Cblk *cblk,
> > +                         int width, int height, int magp, uint8_t roi_shift)
> > +{
> > +    uint8_t p0 = 0;             // Number of placeholder passes
> > +    uint32_t Lcup;              // Length of HT cleanup segment
> > +    uint32_t Lref;              // Length of Refinement segment
> > +    uint32_t Scup;              // HT cleanup segment suffix length
> > +    uint32_t Pcup;              // HT cleanup segment prefix length
> > +
> > +    uint8_t S_blk;              // Number of skipped magnitude bitplanes
> > +    uint8_t pLSB;
> > +
> > +    uint8_t *Dcup;              // Byte of an HT cleanup segment
> > +    uint8_t *Dref;              // Byte of an HT refinement segment
> > +
> > +    int z_blk;                  // Number of ht coding pass
> > +
> > +    uint8_t empty_passes;
> > +
> > +    StateVars mag_sgn;          // Magnitude and Sign
> > +    StateVars mel;              // Adaptive run-length coding
> > +    StateVars vlc;              // Variable Length coding
> > +    StateVars sig_prop;         // Significance propagation
> > +
> > +    MelDecoderState mel_state;
> > +
> > +    int ret;
> > +
> > +    /* Temporary buffers */
> > +    int32_t *sample_buf;
> > +    uint8_t *block_states;
> > +
> > +    int32_t n, val;             // Post-processing
> > +
> > +    int32_t M_b = magp;
> > +    av_assert0(width <= 1024U && height <= 1024U);
> > +    av_assert0(width * height <= 4096);
> > +    av_assert0(width * height > 0);
>
> Has this decoder been tested with some fuzzer ?

Yes.

> I see a bunch of asserts in it and i dont immedeatly see what would prevent them from
> triggering
>
> thx
>
> [...]
> --
> Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> "I am not trying to be anyone's saviour, I'm trying to think about the
>  future and not be sad" - Elon Musk
>
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