[FFmpeg-cvslog] r12593 - trunk/libavcodec/ac3dec.c

[Uoti Urpala]

On Tue, 2008-03-25 at 19:38 -0400, Justin Ruggles wrote:
> jbr wrote:
> > @@ -191,6 +194,7 @@ typedef struct {
> >      GetBitContext gbc;                      ///< bitstream reader
> >      AVRandomState dith_state;               ///< for dither generation
> >      AVCodecContext *avctx;                  ///< parent context
> > +    uint8_t input_buffer[AC3_MAX_FRAME_SIZE];   ///< temp buffer to prevent overread
> >  } AC3DecodeContext;
> 
> Right after I applied this, it occurred to me that it might be better to
> allocate this with av_malloc() at decoder init depending on
> error_resiliance.  Does that sound like a good idea?

I haven't looked at the specific code in this case, but generally moving
a commonly used buffer out of a context struct could hurt performance.
The compiler must either generate extra indirection through the struct
or reserve another register to keep the location of the buffer. OTOH if
time is mostly spent elsewhere, or if accesses to be buffer are not
interleaved with code which would also need to access the struct, then
it might not matter.