On Sat, Nov 14, 2015 at 9:19 PM, Michael Niedermayer <mich...@niedermayer.cc> wrote: > On Sat, Nov 14, 2015 at 12:11:20PM -0500, Ganesh Ajjanagadde wrote: >> This improves the mathematical behavior of hypotenuse computation. >> >> Signed-off-by: Ganesh Ajjanagadde <gajjanaga...@gmail.com> >> --- >> libavutil/eval.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) > > if a hypot() function fallback is added this is ok > otherwise the code as it is before this should be fine too in practice > doubles have a quite large exponent range, half of that is still quite > large
It is not just an issue of overflow, but also accuracy more generally. I gave overflow as the most easily understood issue. Concrete example: 1e-1, 1e-8 actual: 0.100000000000000499999999... hypot: 0.100000000000000505151476 naive: 0.100000000000000519029264 I am pretty sure that the error can be far worse, e.g when bad underflow occurs. There is a fallback, albeit the naive one which Paul does not like, though I myself don't see why in light of your comment above. Rewrote and posted updated version that although not as "perfect" as GNU libm's, is better than a naive sqrt(x*x + y*y). I admit it is a minor thing, on the lines of the log10 stuff, but I posted it as it actually has a greater significance. avutil/eval was used as an illustrative example. > > [...] > -- > Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB > > The real ebay dictionary, page 1 > "Used only once" - "Some unspecified defect prevented a second use" > "In good condition" - "Can be repaird by experienced expert" > "As is" - "You wouldnt want it even if you were payed for it, if you knew ..." > > _______________________________________________ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel > _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
