[Speex-dev] innov_save, what is it? why does it hurt me so?

[Jean-Marc Valin]

> I have been trying to get speex to work for a while now, and it's been
> a real teeter-totter ride.  For a long time I noticed that I will get a
> project to work and then without changing any code and programming it to
> an eprom/flash the project will not work.  

That's an Heisenbug and the most common cause is uninitialised data.

I found innov_save will write over memory it shouldn't be when
> I fill memory with 1's but not when I fill it with zeros. 

Which is normal, see below.

>  When my DSP
> gets to this code chunk:
> if (innov_save){
>    for (i=0;i<st->subframeSize;i++)
>       innov_save[i] = EXTRACT16(PSHR32(innov[i], SIG_SHIFT));
> }

This bit of code is for copying the innov variable to a buffer owned by
the wideband decoder -- but only if there is actually a wideband decoder.

> it will just start filling data in, which it shouldn't.  I see that
> innov_save is set at the beginning of a for loop at:
> for (sub=0;sub<st->nbSubframes;sub++)
>    {
...
>       spx_word16_t *innov_save = NULL;
>       spx_word16_t tmp;...

> but for some reason that never made a difference even though I know I
> stepped over it in the code. 

The reason is doesn't make a difference is that just a few lines later,
you have:

      if (st->innov_save)
         innov_save = st->innov_save+offset;

It means that the innov variable gets copied *unless* st->innov_save
(notice is a field of the encoder struct). So the problem is that this
field is probably not set to NULL. Normally, this is automatically set
to zero when the init function does:
st = (EncState*)speex_alloc(sizeof(EncState));

Is it possible that you did an override of speex_alloc and replaced it
by malloc() instead of calloc() as I'm using? That would explain the
garbage you're getting and it may actually explain other bugs you've had.

	Jean-Marc

> I commented innov save out for now but I
> don't know if there is some case where I might need it.  What does it do
> and do I need it?  Are there any more similar data pointers like that
> that you know of that may cause similar issues?

In any case, about innov_save in general, you can disable all of that if
you're not using wideband.

	Jean-Marc