Re: [FFmpeg-devel] [PATCH 1/4] lavc/h263dsp: add DCT dequantisation functions

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Rémi Denis-Courmont:
> Le lauantaina 6. heinäkuuta 2024, 18.17.37 EEST Andreas Rheinhardt a écrit :
>> Rémi Denis-Courmont:
>>> Note that optimised implementations of these functions will be taken
>>> into actual use only if MpegEncContext.dct_unquantize_h263_{inter,intra}
>>> are *not* overloaded by existing optimisations.
>>> ---
>>>
>>>  libavcodec/h263dsp.c | 25 +++++++++++++++++++++++++
>>>  libavcodec/h263dsp.h |  4 ++++
>>>  2 files changed, 29 insertions(+)
>>>
>>> diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
>>> index 6a13353499..dc146bf821 100644
>>> --- a/libavcodec/h263dsp.c
>>> +++ b/libavcodec/h263dsp.c
>>> @@ -19,10 +19,33 @@
>>>
>>>  #include <stdint.h>
>>>  
>>>  #include "libavutil/attributes.h"
>>>
>>> +#include "libavutil/avassert.h"
>>>
>>>  #include "libavutil/common.h"
>>>  #include "config.h"
>>>  #include "h263dsp.h"
>>>
>>> +static void h263_dct_unquantize_inter_c(int16_t *block, ptrdiff_t len,
>>> +                                        int qmul, int qadd)
>>> +{
>>> +    for (ptrdiff_t i = 0; i <= len; i++) {
>>
>> In the current code, the unquantizing inter does not need an initial
>> check (the compiler can optimize the for-loop to a do-while-like loop).
>> This will be lost here.
> 
> If this not the consequence of your own actions...
> 
> You asked:
> - to use a signed type there, and
> - to avoid the separate initial branch in the intra case.
> 
> And that is exactly how this ends up. You can't have it both ways.
> 

One can have it both ways: Use a do-while loop.

- Andreas

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