Re: [FFmpeg-devel] [PATCHv4 2/4] lavc/mpegvideo: use H263DSP dequant function

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Rémi Denis-Courmont:
> ---
>  libavcodec/mpegvideo.c | 40 +++++++++-------------------------------
>  1 file changed, 9 insertions(+), 31 deletions(-)
> 
> diff --git a/libavcodec/mpegvideo.c b/libavcodec/mpegvideo.c
> index 7af823b8bd..810888fc47 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;
> @@ -219,43 +217,20 @@ static void dct_unquantize_h263_intra_c(MpegEncContext *s,
>      else
>          nCoeffs= s->intra_scantable.raster_end[ s->block_last_index[n] ];
>  
> -    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;
> -        }
> -    }
> +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);

What is the cost of these function calls?

>  }
>  
>  
> @@ -275,6 +250,9 @@ static void gray8(uint8_t *dst, const uint8_t *src, ptrdiff_t linesize, int h)
>  static av_cold int dct_init(MpegEncContext *s)
>  {
>      ff_blockdsp_init(&s->bdsp);
> +#if CONFIG_H263DSP
> +    ff_h263dsp_init(&s->h263dsp);
> +#endif

This ensures that no linking errors happen, but the H.261 codecs will
nevertheless be broken when the H.263 codecs are disabled. In this case
they will try to call a NULL function pointer.

>      ff_hpeldsp_init(&s->hdsp, s->avctx->flags);
>      ff_videodsp_init(&s->vdsp, s->avctx->bits_per_raw_sample);
>  

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