[FFmpeg-devel] [PATCH 1/3] ffv1dec: move slice start finding into a function

[Lynne]

On 06/01/2025 12:40, Michael Niedermayer wrote:
> Hi Lynne
> 
> On Sun, Jan 05, 2025 at 05:59:35PM +0900, Lynne wrote:
>> This also cleans up and gives the code some much needed comments.
>> ---
>>   libavcodec/ffv1dec.c | 66 +++++++++++++++++++++++++++++++-------------
>>   1 file changed, 47 insertions(+), 19 deletions(-)
>>
>> diff --git a/libavcodec/ffv1dec.c b/libavcodec/ffv1dec.c
>> index b7f235c47f..aa988571bc 100644
>> --- a/libavcodec/ffv1dec.c
>> +++ b/libavcodec/ffv1dec.c
>> @@ -866,6 +866,38 @@ static av_cold int decode_init(AVCodecContext *avctx)
>>       return 0;
>>   }
>>   
>> +static int find_next_slice(AVCodecContext *avctx,
>> +                           uint8_t *buf, uint8_t *buf_end, int idx,
>> +                           uint8_t **pos, uint32_t *len)
>> +{
>> +    FFV1Context *f = avctx->priv_data;
>> +
>> +    /* Length field */
>> +    uint32_t v = buf_end - buf;
>> +    if (idx || f->version > 2) {
>> +        /* Three bytes of length, plus flush bit + CRC */
>> +        uint32_t trailer = 3 + 5*!!f->ec;
>> +        if (trailer > buf_end - buf)
>> +            v = INT_MAX;
>> +        else
>> +            v = AV_RB24(buf_end - trailer) + trailer;
>> +    }
>> +
> 
>> +    if (buf_end - buf < v) {
>> +        av_log(avctx, AV_LOG_ERROR, "Slice pointer chain broken\n");
>> +        ff_progress_frame_report(&f->picture, INT_MAX);
>> +        return AVERROR_INVALIDDATA;
>> +    }
> 
> the if() can be moved into the previous if()

I'd prefer to keep it separate to make it cleaner this is a check.
  > the v = buf_end - buf;
> is unused in the first if() so it could be set in an else

I think its cleaner this way, plus its 3 less lines.

> patch LGTM otherwise
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