[FFmpeg-devel] [PATCH 6/6] lavc/flacdsp: document limitations of the LPC encoder

[James Darnley]

On 2014-08-13 04:50, Michael Niedermayer wrote:
> On Tue, Aug 12, 2014 at 11:22:07PM +0200, James Darnley wrote:
>> ---
>>  libavcodec/flacdsp.h |    7 +++++++
>>  1 files changed, 7 insertions(+), 0 deletions(-)
>>
>> diff --git a/libavcodec/flacdsp.h b/libavcodec/flacdsp.h
>> index 272cf2a..36cd904 100644
>> --- a/libavcodec/flacdsp.h
>> +++ b/libavcodec/flacdsp.h
>> @@ -27,6 +27,13 @@ typedef struct FLACDSPContext {
>>                             int len, int shift);
>>      void (*lpc)(int32_t *samples, const int coeffs[32], int order,
>>                  int qlevel, int len);
>> +    /**
>> +     * This function has some limitations with various configurations:
>> +     * - when CONFIG_SMALL is 0 there is an unrolled loop which assumes the
>> +     *   maximum value of order is 32.
>> +     * - when SSE4 (or newer) is available on x86 there is an unrolled copy
>> +     *   which also assumes the maximum value of order is 0.
>> +     */
> 
> sounds like
> 
> printf()
> on fridays with SSE4 this is limited to 27 characters
> 
> a function either should have a limit or not have one, it should
> not depend on other factors
> 
> People using this function must be able to tell in what cases they
> can use it
> 
> and People optimizing the function need to know which cases their
> optimized code must support
> 
> the API defines both

I don't get it.  FLAC only allows upto 32-order LPC.  This was,
apprarently, an acceptable assumption to make for the unrolled C code
yet somehow I can't make the same assumption for assembly.

>> +     *   which also assumes the maximum value of order is 0.
                                                             ^^^
Is it this bit that is confusing?  Because I only now see that typo.  Of
course that should say "32".


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