Re: [FFmpeg-devel] [PATCH 1/4] avcodec/ass: Faster ff_ass_add_rect()

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

Michael Niedermayer:
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/ass.c | 32 ++++++++++++++++++++++++++------
>  libavcodec/ass.h |  7 +++++++
>  2 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/libavcodec/ass.c b/libavcodec/ass.c
> index 725e4d42ba1..d0a4d678bb4 100644
> --- a/libavcodec/ass.c
> +++ b/libavcodec/ass.c
> @@ -114,17 +114,30 @@ char *ff_ass_get_dialog(int readorder, int layer, const char *style,
>                         speaker ? speaker : "", text);
>  }
>  
> -int ff_ass_add_rect(AVSubtitle *sub, const char *dialog,
> +int ff_ass_add_rect2(AVSubtitle *sub, const char *dialog,
>                      int readorder, int layer, const char *style,
> -                    const char *speaker)
> +                    const char *speaker, size_t *nb_rect_allocated)
>  {
> -    AVSubtitleRect **rects, *rect;
> +    AVSubtitleRect **rects = sub->rects, *rect;
>      char *ass_str;
> +    uint64_t new_nb = 0;
>  
> -    rects = av_realloc_array(sub->rects, sub->num_rects+1, sizeof(*sub->rects));
> -    if (!rects)
> +    if (nb_rect_allocated && *nb_rect_allocated <= sub->num_rects) {
> +        new_nb = sub->num_rects + sub->num_rects/16LL + 1;
> +    } else if (!nb_rect_allocated)
> +        new_nb = sub->num_rects + 1LL;
> +    if (new_nb > SIZE_MAX)
>          return AVERROR(ENOMEM);

AVSubtitle.num_rects is unsigned, so this number should always be
bounded by UINT_MAX (and nb_rect_allocated can be a pointer to unsigned,
too).
(Feels like I should resurrect my old av_fast_realloc_array:
https://patchwork.ffmpeg.org/project/ffmpeg/patch/20200101132758.4452-1-andreas.rheinhardt@gmail.com/)

> -    sub->rects = rects;
> +
> +    if (new_nb) {
> +        rects = av_realloc_array(rects, new_nb, sizeof(*sub->rects));
> +        if (!rects)
> +            return AVERROR(ENOMEM);
> +        if (nb_rect_allocated)
> +            *nb_rect_allocated = new_nb;
> +        sub->rects = rects;
> +    }
> +
>      rect       = av_mallocz(sizeof(*rect));
>      if (!rect)
>          return AVERROR(ENOMEM);
> @@ -137,6 +150,13 @@ int ff_ass_add_rect(AVSubtitle *sub, const char *dialog,
>      return 0;
>  }
>  
> +int ff_ass_add_rect(AVSubtitle *sub, const char *dialog,
> +                    int readorder, int layer, const char *style,
> +                    const char *speaker)
> +{
> +    return ff_ass_add_rect2(sub, dialog, readorder, layer, style, speaker, NULL);
> +}
> +
>  void ff_ass_decoder_flush(AVCodecContext *avctx)
>  {
>      FFASSDecoderContext *s = avctx->priv_data;
> diff --git a/libavcodec/ass.h b/libavcodec/ass.h
> index 2c260e4e785..784f46c42c5 100644
> --- a/libavcodec/ass.h
> +++ b/libavcodec/ass.h
> @@ -118,6 +118,13 @@ int ff_ass_add_rect(AVSubtitle *sub, const char *dialog,
>                      int readorder, int layer, const char *style,
>                      const char *speaker);
>  
> +/**
> + * Add an ASS dialog to a subtitle.
> + */
> +int ff_ass_add_rect2(AVSubtitle *sub, const char *dialog,
> +                     int readorder, int layer, const char *style,
> +                     const char *speaker, size_t *nb_rect_allocated);
> +
>  /**
>   * Helper to flush a text subtitles decoder making use of the
>   * FFASSDecoderContext.
> 

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