[FFmpeg-devel] [PATCH 07/12] lpc: remove VLA in ff_lpc_compute_autocorr

[Måns Rullgård]

Justin Ruggles <justin.ruggles at gmail.com> writes:

> M?ns Rullg?rd wrote:
>
>> Justin Ruggles <justin.ruggles at gmail.com> writes:
>> 
>>> Mans Rullgard wrote:
>>>
>>>> ---
>>>>  libavcodec/lpc.c |    4 +++-
>>>>  1 files changed, 3 insertions(+), 1 deletions(-)
>>>>
>>> looks fine to me.  But I think the sse2 version of this function also
>>> has the same VLA.
>> 
>> Yes, it does, as I noticed later.  Requiring dsputil functions to
>> allocate unknown amounts of memory us generally a bad idea.  Can we
>> think of a better solution?  Make the caller pass a scratch buffer?
>
> Well, I am currently working on revising the autocorrelation function,
> mainly for the ALS encoder.  I'm considering splitting out the
> windowing+int32-to-double part into a separate function or set of
> functions.  So maybe we can change the autocorrelation function to take
> double* input, with constraints that it be aligned and that at least
> [-lag] be accessible (with negative array values either already zero or
> containing actual sample values).  This is important for ALS since
> previous sample values need to be included in certain situations.

That's all very well, but doesn't really address the issue of the
dsputil function needing to allocate unbounded amounts of scratch
memory.

-- 
M?ns Rullg?rd
mans at mansr.com