[FFmpeg-devel] [PATCH] mdec: use correctly permutated quant matrix for dequantization.

[James Darnley]

On 2017-06-20 14:47, Ronald S. Bultje wrote:
> This allows using non-simple (e.g. simplemmx) IDCT implementations.
> The result is not bitexact (which is why the fate test continues to
> use -idct simple), but the PSNR between C/MMX goes from ~35 to ~90.
> ---
>  libavcodec/mdec.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/libavcodec/mdec.c b/libavcodec/mdec.c
> index 97bfebb..59658b3 100644
> --- a/libavcodec/mdec.c
> +++ b/libavcodec/mdec.c
> @@ -49,6 +49,7 @@ typedef struct MDECContext {
>      int mb_height;
>      int mb_x, mb_y;
>      DECLARE_ALIGNED(16, int16_t, block)[6][64];
> +    DECLARE_ALIGNED(16, uint16_t, quant_matrix)[64];
>      uint8_t *bitstream_buffer;
>      unsigned int bitstream_buffer_size;
>      int block_last_index[6];
> @@ -61,7 +62,7 @@ static inline int mdec_decode_block_intra(MDECContext *a, int16_t *block, int n)
>      int component;
>      RLTable *rl = &ff_rl_mpeg1;
>      uint8_t * const scantable = a->scantable.permutated;
> -    const uint16_t *quant_matrix = ff_mpeg1_default_intra_matrix;
> +    const uint16_t *quant_matrix = a->quant_matrix;
>      const int qscale = a->qscale;
>  
>      /* DC coefficient */
> @@ -212,9 +213,7 @@ static int decode_frame(AVCodecContext *avctx,
>  static av_cold int decode_init(AVCodecContext *avctx)
>  {
>      MDECContext * const a = avctx->priv_data;
> -
> -    if (avctx->idct_algo == FF_IDCT_AUTO)
> -        avctx->idct_algo = FF_IDCT_SIMPLE;
> +    int i;
>  
>      a->mb_width  = (avctx->coded_width  + 15) / 16;
>      a->mb_height = (avctx->coded_height + 15) / 16;
> @@ -231,6 +230,13 @@ static av_cold int decode_init(AVCodecContext *avctx)
>      avctx->pix_fmt  = AV_PIX_FMT_YUVJ420P;
>      avctx->color_range = AVCOL_RANGE_JPEG;
>  
> +    /* init q matrix */
> +    for (i = 0; i < 64; i++) {
> +        int j = a->idsp.idct_permutation[i];
> +
> +        a->quant_matrix[j] = ff_mpeg1_default_intra_matrix[i];
> +    }
> +
>      return 0;
>  }
>  
> 

That patch seems to work.  FATE doesn't complain when I apply on top of
my others after dropping the one Michael complained about.  That is what
it was supposed to do, right?