[FFmpeg-devel] [PATCH 3/4] avformat/flvenc: Use array instead of linked list for index

[Michael Niedermayer]

On Fri, Oct 25, 2019 at 11:11:46AM +0200, Andreas Rheinhardt wrote:
> Using a linked list had very much overhead (the pointer to the next
> entry increased the size of the index entry struct from 16 to 24 bytes,
> not to mention the overhead of having separate allocations), so it is
> better to (re)allocate a continuous array for the index.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
>  libavformat/flvenc.c | 58 +++++++++++++++-----------------------------
>  1 file changed, 19 insertions(+), 39 deletions(-)
> 
> diff --git a/libavformat/flvenc.c b/libavformat/flvenc.c
> index 0e6c66a5ff..a2bd791c59 100644
> --- a/libavformat/flvenc.c
> +++ b/libavformat/flvenc.c
> @@ -74,7 +74,6 @@ typedef enum {
>  typedef struct FLVFileposition {
>      int64_t keyframe_position;
>      double keyframe_timestamp;
> -    struct FLVFileposition *next;
>  } FLVFileposition;
>  
>  typedef struct FLVContext {
> @@ -108,9 +107,9 @@ typedef struct FLVContext {
>      int acurframeindex;
>      int64_t keyframes_info_offset;
>  
> -    int64_t filepositions_count;
>      FLVFileposition *filepositions;
> -    FLVFileposition *head_filepositions;
> +    size_t filepositions_allocated;
> +    int64_t filepositions_count;
>  
>      AVCodecParameters *audio_par;
>      AVCodecParameters *video_par;
> @@ -549,27 +548,19 @@ static void flv_write_codec_header(AVFormatContext* s, AVCodecParameters* par, i
>  
>  static int flv_append_keyframe_info(AVFormatContext *s, FLVContext *flv, double ts, int64_t pos)
>  {
> -    FLVFileposition *position = av_malloc(sizeof(FLVFileposition));
> -
> -    if (!position) {
> -        av_log(s, AV_LOG_WARNING, "no mem for add keyframe index!\n");
> -        return AVERROR(ENOMEM);
> -    }
> -
> -    position->keyframe_timestamp = ts;
> -    position->keyframe_position = pos;
> -
> -    if (!flv->filepositions_count) {
> -        flv->filepositions = position;
> -        flv->head_filepositions = flv->filepositions;
> -        position->next = NULL;
> -    } else {
> -        flv->filepositions->next = position;
> -        position->next = NULL;
> -        flv->filepositions = flv->filepositions->next;
> +    if (flv->filepositions_count >= flv->filepositions_allocated) {
> +        void *pos = av_realloc_array(flv->filepositions,
> +                                     2 * flv->filepositions_allocated + 1,
> +                                     sizeof(*flv->filepositions));

can the 2* overflow ?
av_fast_realloc() would check for that
i wonder if a av_fast_realloc_array() would make sense

thx

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Never trust a computer, one day, it may think you are the virus. -- Compn
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