[FFmpeg-devel] [PATCHv4 1/4] lavc/h263dsp: add DCT dequantisation functions

[James Almer]

On 6/10/2024 5:23 PM, Rémi Denis-Courmont wrote:
> Note that optimised implementations of these functions will be taken
> into actual use only if MpegEncContext.dct_unquantize_h263_{inter,intra}
> are *not* overloaded by existing optimisations.
> ---
>   libavcodec/h263dsp.c | 25 +++++++++++++++++++++++++
>   libavcodec/h263dsp.h |  4 ++++
>   2 files changed, 29 insertions(+)
> 
> diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
> index 6a13353499..755d7077bf 100644
> --- a/libavcodec/h263dsp.c
> +++ b/libavcodec/h263dsp.c
> @@ -23,6 +23,29 @@
>   #include "config.h"
>   #include "h263dsp.h"
>   
> +static void h263_dct_unquantize_inter_c(int16_t *block, size_t nCoeffs,
> +                                        int qmul, int qadd)
> +{
> +    for (size_t i = 0; i <= nCoeffs; i++) {
> +        int level = block[i];
> +
> +        if (level) {
> +            if (level < 0)
> +                level = level * qmul - qadd;
> +            else
> +                level = level * qmul + qadd;
> +            block[i] = level;
> +        }
> +    }
> +}
> +
> +static void h263_dct_unquantize_intra_c(int16_t *block, size_t nCoeffs,
> +                                        int qmul, int qadd)
> +{
> +    if (nCoeffs > 0)
> +        h263_dct_unquantize_inter_c(block + 1, nCoeffs - 1, qmul, qadd);

I think you can avoid this branch by doing:

     for (size_t i = 1; i <= nCoeffs; i++) {
         int level = block[i];

         if (level) {
             if (level < 0)
                 level = level * qmul - qadd;
             else
                 level = level * qmul + qadd;
             block[i] = level;
         }
     }

> +}
> +
>   const uint8_t ff_h263_loop_filter_strength[32] = {
>       0, 1, 1, 2, 2, 3, 3,  4,  4,  4,  5,  5,  6,  6,  7, 7,
>       7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12
> @@ -116,6 +139,8 @@ static void h263_v_loop_filter_c(uint8_t *src, int stride, int qscale)
>   
>   av_cold void ff_h263dsp_init(H263DSPContext *ctx)
>   {
> +    ctx->h263_dct_unquantize_intra = h263_dct_unquantize_intra_c;
> +    ctx->h263_dct_unquantize_inter = h263_dct_unquantize_inter_c;
>       ctx->h263_h_loop_filter = h263_h_loop_filter_c;
>       ctx->h263_v_loop_filter = h263_v_loop_filter_c;
>   
> diff --git a/libavcodec/h263dsp.h b/libavcodec/h263dsp.h
> index 2dccd23392..0ecbe83314 100644
> --- a/libavcodec/h263dsp.h
> +++ b/libavcodec/h263dsp.h
> @@ -24,6 +24,10 @@
>   extern const uint8_t ff_h263_loop_filter_strength[32];
>   
>   typedef struct H263DSPContext {
> +    void (*h263_dct_unquantize_intra)(int16_t *block /* align 16 */,
> +                                      size_t len, int mul, int add);
> +    void (*h263_dct_unquantize_inter)(int16_t *block /* align 16 */,
> +                                      size_t len, int mul, int add);
>       void (*h263_h_loop_filter)(uint8_t *src, int stride, int qscale);
>       void (*h263_v_loop_filter)(uint8_t *src, int stride, int qscale);
>   } H263DSPContext;