[FFmpeg-devel] [PATCH] ffprobe: avoid unnecessary pow and exp2 calls

[Ganesh Ajjanagadde]

On Tue, Dec 29, 2015 at 3:04 AM, Stefano Sabatini <stefasab at gmail.com> wrote:
> On date Wednesday 2015-12-23 09:56:17 -0800, Ganesh Ajjanagadde encoded:
>> These are just for prefixes and may be hardcoded easily; see lavu/eval
>> for this approach.
>>
>> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
>> ---
>>  ffprobe.c | 27 +++++++++++++++++++--------
>>  1 file changed, 19 insertions(+), 8 deletions(-)
>>
>> diff --git a/ffprobe.c b/ffprobe.c
>> index 0b672ff..c352b44 100644
>> --- a/ffprobe.c
>> +++ b/ffprobe.c
>> @@ -218,8 +218,19 @@ static AVInputFormat *iformat = NULL;
>>
>>  static struct AVHashContext *hash;
>>
>> -static const char *const binary_unit_prefixes [] = { "", "Ki", "Mi", "Gi", "Ti", "Pi" };
>> -static const char *const decimal_unit_prefixes[] = { "", "K" , "M" , "G" , "T" , "P"  };
>> +static const struct {
>> +    double bin_val;
>> +    double dec_val;
>> +    const char *bin_str;
>> +    const char *dec_str;
>> +} si_prefixes[] = {
>> +    { 1.0, 1.0, "", "" },
>> +    { 1.024e3, 1e3, "Ki", "K" },
>> +    { 1.048576e6, 1e6, "Mi", "M" },
>> +    { 1.073741824e9, 1e9, "Gi", "G" },
>> +    { 1.099511627776e12, 1e12, "Ti", "T" },
>> +    { 1.125899906842624e15, 1e15, "Pi", "P" },
>> +};
>>
>>  static const char unit_second_str[]         = "s"    ;
>>  static const char unit_hertz_str[]          = "Hz"   ;
>> @@ -273,14 +284,14 @@ static char *value_string(char *buf, int buf_size, struct unit_value uv)
>>
>>              if (uv.unit == unit_byte_str && use_byte_value_binary_prefix) {
>>                  index = (long long int) (log2(vald)) / 10;
>> -                index = av_clip(index, 0, FF_ARRAY_ELEMS(binary_unit_prefixes) - 1);
>> -                vald /= exp2(index * 10);
>> -                prefix_string = binary_unit_prefixes[index];
>> +                index = av_clip(index, 0, FF_ARRAY_ELEMS(si_prefixes) - 1);
>> +                vald /= si_prefixes[index].bin_val;
>> +                prefix_string = si_prefixes[index].bin_str;
>>              } else {
>>                  index = (long long int) (log10(vald)) / 3;
>> -                index = av_clip(index, 0, FF_ARRAY_ELEMS(decimal_unit_prefixes) - 1);
>> -                vald /= pow(10, index * 3);
>> -                prefix_string = decimal_unit_prefixes[index];
>> +                index = av_clip(index, 0, FF_ARRAY_ELEMS(si_prefixes) - 1);
>> +                vald /= si_prefixes[index].dec_val;
>> +                prefix_string = si_prefixes[index].dec_str;
>>              }
>>              vali = vald;
>>          }
>> --
>> 2.6.4
>
> LGTM, thanks.

pushed, thanks

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