On Fri, Dec 25, 2015 at 6:27 PM, Ganesh Ajjanagadde <gajja...@mit.edu> wrote: > On Fri, Dec 25, 2015 at 9:26 AM, James Almer <jamr...@gmail.com> wrote: >> On 12/25/2015 2:11 PM, Ganesh Ajjanagadde wrote: >>> Fast, reasonably accurate 10^x. Alternative of detection of libm exp10 at >>> configure >>> time is not worth the trouble, since it is anyway not POSIX or ISO C, >>> and currently only the GNU libm has it. Furthermore, GNU libm's variant >>> is ~ 2x slower, and is ironically not correctly rounded (2 ulp off) to >>> justify all >>> that slowdown. >>> >>> Reviewed-by: Michael Niedermayer <mich...@niedermayer.cc> >>> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> >>> --- >>> libavutil/internal.h | 19 +++++++++++++++++++ >>> 1 file changed, 19 insertions(+) >>> >>> diff --git a/libavutil/internal.h b/libavutil/internal.h >>> index f86b7fb..ae11601 100644 >>> --- a/libavutil/internal.h >>> +++ b/libavutil/internal.h >>> @@ -292,6 +292,25 @@ static av_always_inline av_const int64_t >>> ff_rint64_clip(double a, int64_t amin, >>> return res; >>> } >>> >>> +/** >>> + * Compute 10^x for floating point values. Note: this function is by no >>> means >>> + * "correctly rounded", and is meant as a fast, reasonably accurate >>> approximation. >>> + * For instance, maximum relative error for the double precision variant is >>> + * ~ 1e-13 for very small and very large values. >>> + * This is ~2x faster than GNU libm's approach, which is still off by 2ulp >>> on >>> + * some inputs. >>> + * @param x exponent >>> + * @return 10^x >>> + */ >>> +static av_always_inline double avpriv_exp10(double x) >> >> It's an inline function in a header, and internal at that. Just call it >> ff_exp10. > > It is used in avcodec and avfilter. I thought this meant that it > should be avpriv? > Personally, I like ff_exp10 as it is shorter. >
avpriv is a hack for private functions that need to be exported in shared libraries, since we have a rule to only export av* functions. inline functions in headers don't need to be exported in a library, so no need for avpriv. ff* is fine there, and used for other similar situations. - Hendrik _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
