[FFmpeg-devel] [PATCH 2/2] mips: Optimization of AC3 FP encoder and EAC3 FP decoder

[Vitor Sessak]

Hi!

On 10/16/2012 04:26 PM, Nedeljko Babic wrote:
> Signed-off-by: Nedeljko Babic <nbabic at mips.com>
> ---

> --- a/libavcodec/ac3enc.h
> +++ b/libavcodec/ac3enc.h
> @@ -256,6 +256,8 @@ typedef struct AC3EncodeContext {
>       /* fixed vs. float templated function pointers */
>       int  (*allocate_sample_buffers)(struct AC3EncodeContext *s);
>
> +    void (*apply_mdct)(struct AC3EncodeContext *s);

Strange. C code for apply_mdct() is basically just calling a 
DSPContext.apply_window() inside a loop. So why do you need to make an 
ASM version out of it instead of just writing a MIPS version of 
apply_window()? Is the function call is too expensive?

> +static void ff_ac3_float_apply_channel_coupling_mips(AC3EncodeContext *s)
> +{
> +    LOCAL_ALIGNED_16(CoefType, cpl_coords,      [AC3_MAX_BLOCKS], [AC3_MAX_CHANNELS][16]);
> +    LOCAL_ALIGNED_16(int32_t, fixed_cpl_coords, [AC3_MAX_BLOCKS], [AC3_MAX_CHANNELS][16]);
> +    int blk, ch, bnd, i, j;
> +    CoefSumType energy[AC3_MAX_BLOCKS][AC3_MAX_CHANNELS][16] = {{{0}}};
> +    int cpl_start, num_cpl_coefs;
> +    int32_t  *dst;
> +    const float *src;
> +    unsigned int len;
> +    uint8_t *exp;
> +    float scale = 1 << 24;
> +    float src0, src1, src2, src3, src4, src5, src6, src7;
> +    int temp0, temp1, temp2, temp3, temp4, temp5, temp6, temp7;
> +    int e,v;

Wow, this is a pretty complex function and optimizing it this way makes 
for a lot of code duplication. Can't you just extract the time-consuming 
parts to some DSP function?

-Vitor