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

[Stefano Sabatini]

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.
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