[FFmpeg-soc] [PATCH] jpeg2k : support higher sample precision

[Michael Niedermayer]

On Sun, Jul 05, 2009 at 12:02:27PM +0000, Jai Menon wrote:
> On Sun, Jun 28, 2009 at 12:06 PM, Michael Niedermayer<michaelni at gmx.at> wrote:
> > On Sat, Jun 27, 2009 at 08:25:43PM +0000, Jai Menon wrote:
> >> On Thu, Jun 25, 2009 at 9:51 PM, Michael Niedermayer<michaelni at gmx.at> wrote:
> >> > On Wed, Jun 24, 2009 at 05:59:19PM +0000, Jai Menon wrote:
> >> >> On Wed, Jun 24, 2009 at 3:58 PM, Michael Niedermayer<michaelni at gmx.at> wrote:
> >> >> > On Wed, Jun 24, 2009 at 01:42:08PM +0000, Jai Menon wrote:
> >> >> >> On Wed, Jun 24, 2009 at 1:27 PM, Michael Niedermayer<michaelni at gmx.at> wrote:
> >> >> >> > On Sun, Jun 21, 2009 at 04:35:20PM +0000, Jai Menon wrote:
> >> >> > [...]
> >> >> >> > [...]
> >> >> >> >> @@ -806,6 +815,26 @@
> >> >> >> >>
> >> >> >> >>          line += s->picture.linesize[0];
> >> >> >> >>      }
> >> >> >> >> +    } else {
> >> >> >> >> +        for (; y < tile->comp[0].coord[1][1] - s->image_offset_y; y++) {
> >> >> >> >> +            uint16_t *dst;
> >> >> >> >> +            x = tile->comp[0].coord[0][0] - s->image_offset_x;
> >> >> >> >> +            dst = line + x * s->ncomponents * 2;
> >> >> >> >> +            for (; x < tile->comp[0].coord[0][1] - s->image_offset_x; x++) {
> >> >> >> >> +                for (compno = 0; compno < s->ncomponents; compno++) {
> >> >> >> >
> >> >> >> >> +                    *src[compno] = av_rescale(*src[compno], (1 << 16) - 1,
> >> >> >> >> +                                              (1 << s->cbps[compno]) - 1);
> >> >> >> >
> >> >> >> > av_rescale is too slow
> >> >> >>
> >> >> >> So just (*src[compno]/((1 << s->cbps[compno]) - 1)) * ((1 << 16) - 1) ?
> >> >> >
> >> >> > * is slow
> >> >> > / s slower
> >> >> >
> >> >> > "src" << C
> >> >> > it should be
> >> >>
> >> >> <possibly dumb question ahead>
> >> >>
> >> >> I understand that * and / are slower but how can I achieve the same
> >> >> effect with a single <<?
> >> >
> >> > well, not the same but close enough IMHO
> >> > src<<C
> >> > or
> >> > (src<<C) + (src>>(16-C))
> >> > should be close enough, my point was mainly that av_rescale() is too slow
> >> > to be done per pixel and anything else is better
> >>
> >> Okay, modified patch attached.
> >
> > [...]
> >> @@ -806,6 +815,22 @@
> >>
> >>          line += s->picture.linesize[0];
> >>      }
> >> +    } else {
> >> +        for (; y < tile->comp[0].coord[1][1] - s->image_offset_y; y++) {
> >> +            uint16_t *dst;
> >> +            x = tile->comp[0].coord[0][0] - s->image_offset_x;
> >> +            dst = line + x * s->ncomponents * 2;
> >> +            for (; x < tile->comp[0].coord[0][1] - s->image_offset_x; x++) {
> >> +                for (compno = 0; compno < s->ncomponents; compno++) {
> >> +                    *src[compno] = *src[compno] << (16 - s->cbps[compno]);
> >> +                    *src[compno] += 1 << 15;
> >> +                    *src[compno] = av_clip(*src[compno], 0, (1 << 16) - 1);
> >> +                    *dst++ = *src[compno]++;
> >
> > i dont think using *src[compno] as a temporary is a good choice
> 
> You mean *src[compno] should be copied to dst and all operations
> should be done on dst?
> Current approach seemed correct because this a part of level shifting.
> Or did i misunderstand?

int val= src << ...
val += ...
val = av_clip(...)
*dst++= val;

its easy for the compiler to put val in a register, doing t with src is not
because it would have to proof that src is not read after it


[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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