Servus Michael,
On Wed, Jun 4, 2025 at 1:00 PM Michael Niedermayer
<mich...@niedermayer.cc> wrote:
>
> On Tue, Jun 03, 2025 at 12:30:40PM +0200, Manuel Lauss wrote:
> > Servus Michael,
> >
> > On Sat, May 31, 2025 at 12:51 AM Michael Niedermayer
> > <mich...@niedermayer.cc> wrote:
> >
> > > > > > /* smooth top and left block borders with neighbours */
> > > > > > - if (((pxoff - p + k) < 0) || ((pxoff - p + k) >=
> > > > > > maxpxo)
> > > > > > + if (((pxoff - p + 0) < 0) || ((pxoff - p + k) >=
> > > > > > maxpxo)
> > > > > > || ((pxoff + 3 * p) < 0) || ((pxoff + 3 * p) >=
> > > > > > maxpxo)
> > > > > > || (i == 0) || (j == 0))
> > > > > > continue;
> > > >
> > > > Oops, yes, that change is correct.
> > >
> > > will apply
> > >
> > >
> > > > I think you should just rip the whole block-smoothing block out
> > > > entirely: it creates a "sawtooth" pattern
> > > > which is more annoying than the "blockiness" it tries to soften.
> > >
> > > probably, but i just wanted to fix the out of array access,
> > > ill leave improvment beyond that to others
> >
> > Is it OK if I just remove this block entirely? I'd commit that along
> > with the other 2 sanm patches I have.
>
> i think you dont understand the bug my change is fixing
>
> Its an out of array access in:
> for (k = 0; k < 4; k++)
> *(dst + pxoff + k) = ((*(dst + pxoff + k) + *(dst + pxoff
> - p + k)) >> 1) & 0x7f;
>
> The hunk:
> /* smooth top and left block borders with neighbours */
> if (((pxoff - p + k) < 0) || ((pxoff - p + k) >= maxpxo)
> || ((pxoff + 3 * p) < 0) || ((pxoff + 3 * p) >= maxpxo)
> || (i == 0) || (j == 0))
> continue;
>
> skips this code. If the hunk is removed and nothing else is changed
> its MORE buggy as there will be more out of array accesses
I was thinking about this:
diff --git a/libavcodec/sanm.c b/libavcodec/sanm.c
index 00bfef00fe..5912a8c14b 100644
--- a/libavcodec/sanm.c
+++ b/libavcodec/sanm.c
@@ -732,25 +732,6 @@ static int old_codec4(SANMVideoContext *ctx,
GetByteContext *gb, int top, int le
}
pxo2 = pxo2 - 4 + p;
}
-
- /* smooth top and left block borders with neighbours */
- if (((pxoff - p + k) < 0) || ((pxoff - p + k) >= maxpxo)
- || ((pxoff + 3 * p) < 0) || ((pxoff + 3 * p) >= maxpxo)
- || (i == 0) || (j == 0))
- continue;
- if (param & 0x80) {
- for (k = 0; k < 4; k++)
- *(dst + pxoff + k) = ((*(dst + pxoff + k) + *(dst
+ pxoff - p + k)) >> 1) | 0x80;
- *(dst + pxoff + 1 * p) = (*(dst + pxoff + 1 * p) +
*(dst + pxoff + 1 * p - 1)) >> 1 | 0x80;
- *(dst + pxoff + 2 * p) = (*(dst + pxoff + 2 * p) +
*(dst + pxoff + 2 * p - 1)) >> 1 | 0x80;
- *(dst + pxoff + 3 * p) = (*(dst + pxoff + 3 * p) +
*(dst + pxoff + 3 * p - 1)) >> 1 | 0x80;
- } else {
- for (k = 0; k < 4; k++)
- *(dst + pxoff + k) = ((*(dst + pxoff + k) + *(dst
+ pxoff - p + k)) >> 1) & 0x7f;
- *(dst + pxoff + 1 * p) = (*(dst + pxoff + 1 * p) +
*(dst + pxoff + 1 * p - 1)) >> 1;
- *(dst + pxoff + 2 * p) = (*(dst + pxoff + 2 * p) +
*(dst + pxoff + 2 * p - 1)) >> 1;
- *(dst + pxoff + 3 * p) = (*(dst + pxoff + 3 * p) +
*(dst + pxoff + 3 * p - 1)) >> 1;
- }
}
}
return 0;
Manuel
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