opus - Mar 2011 - fixed point code

Hi,

I am looking into fixed-point code of the CELT decoder for real-time
application. Here are some questions..

[1] array, window[]
The array, window[] is being initialized from a function below in modes.c. This
array  is being initialized differently for the decoder, depending on frame size
and sampling freq. of the bitstream ..

Could you provide us with fixed-point code for initialization of this array? Or
you may kindly provide us with ROM tables of the array for each possible
combination of frame size and sampling freq...?


CELTMode *celt_mode_create(celt_int32 Fs, int frame_size, int *error)
{

....
....

#ifndef FIXED_POINT
   for (i=0;i<mode->overlap;i++)
      window[i] = Q15ONE*sin(.5*M_PI* sin(.5*M_PI*(i+.5)/mode->overlap) *
sin(.5*M_PI*(i+.5)/mode->overlap));
#else
   for (i=0;i<mode->overlap;i++)
      window[i] = MIN32(32767,floor(.5+32768.*sin(.5*M_PI*
sin(.5*M_PI*(i+.5)/mode->overlap) * sin(.5*M_PI*(i+.5)/mode->overlap))));
#endif

.....
.....

}

[2] Usage on global stack memory

In "arch.h", there is a definition on the following constant for
global processing memory (stack RAM).

#define GLOBAL_STACK_SIZE 100000

Then, dynamic RAM is allocated through calloc (GLOBAL_STACK_SIZE, 1), which
means that 100,000 bytes of RAM is being allocated for decoder processing. Do we
really need 100KB RAM for decoder processing (whatever called ... processing RAM
or stack RAM)?

What's peak R/W RAM requirement of the CELT decoder?

-          Peak state memory (static RAM) size?

-          Peak processing RAM size including local stack RAM (100,000 bytes?)?

-          Minimum input bit-stream buffer size with maximum bit-rate per frame
considered at 48KHz sampling rate?

(for example, in AAC, 1536 bytes of input bitstream buffer needed for a frame of
decoding since 576kbps is the highest bit-rate in stereo channel at 48KHz
sampling rate)?



Cheers,
//JB Hong


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Hi,

"J.B. (Jae) Hong" <jbhong at broadcom.com> a
?crit?:
> Could you provide us with fixed-point code for initialization of  
> this array? Or you may kindly provide us with ROM tables of the  
> array for each possible combination of frame size and sampling  
> freq...?
ROM tables are already included for frame sizes 120,240,480,960 at 48  
kHz. For the others, you can use the dump_modes utility with the  
sampling rate(s) and frame size(s) you need.
> [2] Usage on global stack memory
>
> In "arch.h", there is a definition on the following constant for
> global processing memory (stack RAM).
>
> #define GLOBAL_STACK_SIZE 100000
This "global stack" is only a fall-back when neither C99  
variable-length arrays, nor alloca() are available. See if you can use  
one of those instead. For that, all you need is define either  
VAR_ARRAYS or USE_ALLOCA.
> -          Peak state memory (static RAM) size?
>
> -          Peak processing RAM size including local stack RAM  
> (100,000 bytes?)?
I have not measured those, but I'm sure it's under 100k. Also, it's
probably possible to make CELT more efficient than it currently is  
when it comes to stack size.
> -          Minimum input bit-stream buffer size with maximum  
> bit-rate per frame considered at 48KHz sampling rate?
If by that you mean the largest compressed packet that can exist, then  
the answer is 1275 bytes.

    Jean-Marc