[FFmpeg-devel] [PATCH 1/2] avcodec/alacdec: split off decorrelate_stereo and append_extra_bits as alacdsp

[James Almer]

On 10/4/2015 12:44 AM, James Almer wrote:
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavcodec/Makefile  |  2 +-
>  libavcodec/alac.c    | 65 +++++++++++++++++++---------------------------------
>  libavcodec/alacdsp.c | 57 +++++++++++++++++++++++++++++++++++++++++++++
>  libavcodec/alacdsp.h | 35 ++++++++++++++++++++++++++++
>  4 files changed, 116 insertions(+), 43 deletions(-)
>  create mode 100644 libavcodec/alacdsp.c
>  create mode 100644 libavcodec/alacdsp.h
> 
> diff --git a/libavcodec/Makefile b/libavcodec/Makefile
> index b15e431..153c3f8 100644
> --- a/libavcodec/Makefile
> +++ b/libavcodec/Makefile
> @@ -143,7 +143,7 @@ OBJS-$(CONFIG_AC3_ENCODER)             += ac3enc_float.o ac3enc.o ac3tab.o \
>                                            ac3.o kbdwin.o
>  OBJS-$(CONFIG_AC3_FIXED_ENCODER)       += ac3enc_fixed.o ac3enc.o ac3tab.o ac3.o
>  OBJS-$(CONFIG_AIC_DECODER)             += aic.o
> -OBJS-$(CONFIG_ALAC_DECODER)            += alac.o alac_data.o
> +OBJS-$(CONFIG_ALAC_DECODER)            += alac.o alac_data.o alacdsp.o
>  OBJS-$(CONFIG_ALAC_ENCODER)            += alacenc.o alac_data.o
>  OBJS-$(CONFIG_ALIAS_PIX_DECODER)       += aliaspixdec.o
>  OBJS-$(CONFIG_ALIAS_PIX_ENCODER)       += aliaspixenc.o
> diff --git a/libavcodec/alac.c b/libavcodec/alac.c
> index 827c0db..b767438 100644
> --- a/libavcodec/alac.c
> +++ b/libavcodec/alac.c
> @@ -57,6 +57,7 @@
>  #include "unary.h"
>  #include "mathops.h"
>  #include "alac_data.h"
> +#include "alacdsp.h"
>  
>  #define ALAC_EXTRADATA_SIZE 36
>  
> @@ -81,6 +82,8 @@ typedef struct ALACContext {
>  
>      int direct_output;
>      int extra_bit_bug;
> +
> +    ALACDSPContext dsp;
>  } ALACContext;
>  
>  static inline unsigned int decode_scalar(GetBitContext *gb, int k, int bps)
> @@ -230,35 +233,6 @@ static void lpc_prediction(int32_t *error_buffer, int32_t *buffer_out,
>      }
>  }
>  
> -static void decorrelate_stereo(int32_t *buffer[2], int nb_samples,
> -                               int decorr_shift, int decorr_left_weight)
> -{
> -    int i;
> -
> -    for (i = 0; i < nb_samples; i++) {
> -        int32_t a, b;
> -
> -        a = buffer[0][i];
> -        b = buffer[1][i];
> -
> -        a -= (b * decorr_left_weight) >> decorr_shift;
> -        b += a;
> -
> -        buffer[0][i] = b;
> -        buffer[1][i] = a;
> -    }
> -}
> -
> -static void append_extra_bits(int32_t *buffer[2], int32_t *extra_bits_buffer[2],
> -                              int extra_bits, int channels, int nb_samples)
> -{
> -    int i, ch;
> -
> -    for (ch = 0; ch < channels; ch++)
> -        for (i = 0; i < nb_samples; i++)
> -            buffer[ch][i] = (buffer[ch][i] << extra_bits) | extra_bits_buffer[ch][i];
> -}
> -
>  static int decode_element(AVCodecContext *avctx, AVFrame *frame, int ch_index,
>                            int channels)
>  {
> @@ -389,19 +363,24 @@ static int decode_element(AVCodecContext *avctx, AVFrame *frame, int ch_index,
>          decorr_left_weight = 0;
>      }
>  
> -    if (alac->extra_bits && alac->extra_bit_bug) {
> -        append_extra_bits(alac->output_samples_buffer, alac->extra_bits_buffer,
> -                          alac->extra_bits, channels, alac->nb_samples);
> -    }
> +    if (channels == 2) {
> +        if (alac->extra_bits && alac->extra_bit_bug) {
> +            alac->dsp.append_extra_bits_stereo(alac->output_samples_buffer, alac->extra_bits_buffer,
> +                                               alac->extra_bits, channels, alac->nb_samples);
> +        }
>  
> -    if (channels == 2 && decorr_left_weight) {
> -        decorrelate_stereo(alac->output_samples_buffer, alac->nb_samples,
> -                           decorr_shift, decorr_left_weight);
> -    }
> +        if (decorr_left_weight) {

So while i was writing a checkasm unit i started looking at the possible
values for this, and found out that apparently it's either 0 or 1.
Since the function below is not called when it's 0, wouldn't that mean
it's a pointless argument?

I'll have to redo the asm function if that's the case, and change the
prototype and boilerplate c version.

> +            alac->dsp.decorrelate_stereo(alac->output_samples_buffer, alac->nb_samples,
> +                                         decorr_shift, decorr_left_weight);
> +        }