On Mon, Jun 10, 2024 at 03:14:14PM +0300, Rémi Denis-Courmont wrote:
>
>
> Le 10 juin 2024 14:41:31 GMT+03:00, Michael Niedermayer
> <mich...@niedermayer.cc> a écrit :
> >On Sun, Jun 09, 2024 at 07:23:45PM +0300, Rémi Denis-Courmont wrote:
> >> ---
> >> libavcodec/mpegvideo.c | 44 ++++++++++--------------------------------
> >> 1 file changed, 10 insertions(+), 34 deletions(-)
> >>
> >> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> >> index 7af823b8bd..9be0fecc8d 100644
> >> --- a/libavcodec/mpegvideo.c
> >> +++ b/libavcodec/mpegvideo.c
> >> @@ -201,13 +201,11 @@ static void
> >> dct_unquantize_mpeg2_inter_c(MpegEncContext *s,
> >> static void dct_unquantize_h263_intra_c(MpegEncContext *s,
> >> int16_t *block, int n, int qscale)
> >> {
> >> - int i, level, qmul, qadd;
> >> - int nCoeffs;
> >> + int qmul = qscale << 1;
> >> + int qadd, nCoeffs;
> >>
> >> av_assert2(s->block_last_index[n]>=0 || s->h263_aic);
> >>
> >> - qmul = qscale << 1;
> >> -
> >> if (!s->h263_aic) {
> >> block[0] *= n < 4 ? s->y_dc_scale : s->c_dc_scale;
> >> qadd = (qscale - 1) | 1;
> >> @@ -215,47 +213,24 @@ static void
> >> dct_unquantize_h263_intra_c(MpegEncContext *s,
> >> qadd = 0;
> >> }
> >> if(s->ac_pred)
> >> - nCoeffs=63;
> >> + nCoeffs = 64;
> >> else
> >> - nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
> >> + nCoeffs = s->intra_scantable.raster_end[s->block_last_index[n]] +
> >> 1;
> >>
> >> - for(i=1; i<=nCoeffs; i++) {
> >> - level = block[i];
> >> - if (level) {
> >> - if (level < 0) {
> >> - level = level * qmul - qadd;
> >> - } else {
> >> - level = level * qmul + qadd;
> >> - }
> >> - block[i] = level;
> >> - }
> >> - }
> >> + s->h263dsp.h263_dct_unquantize_intra(block, nCoeffs, qmul, qadd);
> >> }
> >>
> >> static void dct_unquantize_h263_inter_c(MpegEncContext *s,
> >> int16_t *block, int n, int qscale)
> >> {
> >> - int i, level, qmul, qadd;
> >> + int qmul = qscale << 1;
> >> + int qadd = (qscale - 1) | 1;
> >> int nCoeffs;
> >>
> >> av_assert2(s->block_last_index[n]>=0);
> >>
> >> - qadd = (qscale - 1) | 1;
> >> - qmul = qscale << 1;
> >> -
> >> - nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> >> -
> >> - for(i=0; i<=nCoeffs; i++) {
> >> - level = block[i];
> >> - if (level) {
> >> - if (level < 0) {
> >> - level = level * qmul - qadd;
> >> - } else {
> >> - level = level * qmul + qadd;
> >> - }
> >> - block[i] = level;
> >> - }
> >> - }
> >> + nCoeffs = s->inter_scantable.raster_end[s->block_last_index[n]] + 1;
> >> + s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
> >
> >It would be better if the "+ 1" would not be needed and teh functions
> >would keep using "<="
>
> Why?because its 1 instruction less and the compieler cannot optimize it out. > AFAICT, that just makes the assembler more confusing by requiring an unusual > boundary check. > > And then for SVE and RVV, adding one is unavoidable possible, as we need the > element count to predicate the vector ops. So we'd just end up having to add > one in the assembler instead of C. [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB If a bugfix only changes things apparently unrelated to the bug with no further explanation, that is a good sign that the bugfix is wrong.
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