Re: [FFmpeg-devel] [PATCH 6/7] avcodec/put_bits: add put_leb()

[James Almer <jamrial@gmail.com>]

On 1/30/2024 7:10 PM, Andreas Rheinhardt wrote:
> James Almer:
>> On 1/30/2024 6:53 PM, Andreas Rheinhardt wrote:
>>> James Almer:
>>>> Signed-off-by: James Almer <jamrial@gmail.com>
>>>> ---
>>>>    libavcodec/put_bits.h | 16 ++++++++++++++++
>>>>    1 file changed, 16 insertions(+)
>>>>
>>>> diff --git a/libavcodec/put_bits.h b/libavcodec/put_bits.h
>>>> index 4561dc131a..04dedd3342 100644
>>>> --- a/libavcodec/put_bits.h
>>>> +++ b/libavcodec/put_bits.h
>>>> @@ -370,6 +370,22 @@ static inline void put_sbits63(PutBitContext
>>>> *pb, int n, int64_t value)
>>>>        put_bits64(pb, n, (uint64_t)(value) & (~(UINT64_MAX << n)));
>>>>    }
>>>>    +static inline void put_leb(PutBitContext *s, unsigned value)
>>>> +{
>>>> +    int len;
>>>> +    uint8_t byte;
>>>> +
>>>> +    len = (av_log2(value) + 7) / 7;
>>>> +
>>>> +    for (int i = 0; i < len; i++) {
>>>> +        byte = value >> (7 * i) & 0x7f;
>>>> +        if (i < len - 1)
>>>> +            byte |= 0x80;
>>>> +
>>>> +        put_bits_no_assert(s, 8, byte);
>>>> +    }
>>>> +}
>>>> +
>>>>    /**
>>>>     * Return the pointer to the byte where the bitstream writer will put
>>>>     * the next bit.
>>>
>>> This function does use any internals of PutBitContext and should
>>> therefore be in user-code. In fact, get_leb() should not exist in
>>> get_bits.h.
>>
>> You could say the same about skip_1stop_8data_bits(), decode210(),
>> decode012() and get_vlc_multi().
> 
> Old errors do not justify new errors.
> (skip_1stop_8data_bits() is mostly mpegvideodec and if it were not for
> SVQ3 it would have been moved there already.)
> 
>>
>> And the idea is to have these be reusable. leb is evidently going to be
>> used by anything AOMedia will make.
> 
> Then it should be in some AOMedia header. If it should exist at all:
> Byte-aligned lebs should not use a GetBitContext at all. And all current
> users are byte-aligned.

All lebs are byte aligned. And of course we need a GetBitContext 
implementation when we need to read elements as small as 1 bit followed 
by a leb followed by some other form of vlc when parsing a single header.

And ok, I can move these to an AOM specific header if you prefer.

> 
> - Andreas
> 
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