[FFmpeg-devel] [PATCH v2] avfilter/formats: optimize ff_all_formats

[zhilizhao]

> On Dec 10, 2019, at 4:20 AM, Tomas Härdin <tjoppen at acc.umu.se> wrote:
> 
> lör 2019-12-07 klockan 01:06 +0800 skrev Zhao Zhili:
>> This is a micro-optimization. Saving almost 200 reallocations makes
>> it
>> worth a try.
>> ---
>> fix commit message typo: relocations -> reallocations
>> 
>> libavfilter/formats.c | 35 +++++++++++++++++++++--------------
>> 1 file changed, 21 insertions(+), 14 deletions(-)
>> 
>> diff --git a/libavfilter/formats.c b/libavfilter/formats.c
>> index 33c64668a0..1af7a1cedd 100644
>> --- a/libavfilter/formats.c
>> +++ b/libavfilter/formats.c
>> @@ -348,23 +348,30 @@ int
>> ff_add_channel_layout(AVFilterChannelLayouts **l, uint64_t
>> channel_layout)
>> 
>> AVFilterFormats *ff_all_formats(enum AVMediaType type)
>> {
>> -    AVFilterFormats *ret = NULL;
>> +    AVFilterFormats *ret;
>> +    int i, count;
>> 
>> -    if (type == AVMEDIA_TYPE_VIDEO) {
>> -        const AVPixFmtDescriptor *desc = NULL;
>> -        while ((desc = av_pix_fmt_desc_next(desc))) {
>> -            if (ff_add_format(&ret, av_pix_fmt_desc_get_id(desc)) <
>> 0)
>> -                return NULL;
>> -        }
>> -    } else if (type == AVMEDIA_TYPE_AUDIO) {
>> -        enum AVSampleFormat fmt = 0;
>> -        while (av_get_sample_fmt_name(fmt)) {
>> -            if (ff_add_format(&ret, fmt) < 0)
>> -                return NULL;
>> -            fmt++;
>> -        }
>> +    if (type == AVMEDIA_TYPE_VIDEO)
>> +        count = AV_PIX_FMT_NB;
>> +    else if (type == AVMEDIA_TYPE_AUDIO)
>> +        count = AV_SAMPLE_FMT_NB;
>> +    else
>> +        return NULL;
>> +
>> +    ret = av_mallocz(sizeof(*ret));
>> +    if (!ret)
>> +        return NULL;
>> +
>> +    ret->nb_formats = count;
>> +    ret->formats = av_malloc_array(count, sizeof(*ret->formats));
>> +    if (!ret->formats) {
>> +        av_free(ret);
>> +        return NULL;
>>     }
>> 
>> +    for (i = 0; i < count; i++)
>> +        ret->formats[i] = i;
> 
> As far as I can tell this is OK, and it passes FATE. But it just looks
> very very wrong. Why does this function even exist if all it
> effectively does is return the integers from 0..count-1?

The function is there since the first libavfilter commit. I guess it’s for forward compatibility.

I don’t know whether a ‘all_formats’ flag works or not.

> 
> /Tomas
> 
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