Thank you all! Everything is clear.
Tim On Wed, 30 Apr 2025, at 10:07 AM, Tomas Kalibera wrote: > On 4/30/25 10:43, Tim Taylor wrote: >> Cheers for the quick response. >> >> To clarify my question: Is it correct to say that as long as packages do not >> assume the greater precision provided by 'double' there is no reason they >> cannot use 'long double' to get *possible* advantages (e.g. in summations). >> AFAICT 'long double' is (and has always been) part of the C standard so it's >> use as a type should be unproblematic (this is the query relevant to >> matrixStats). > > Probably already clear from previous answers, but yes, packages can use > long double type. > > Whenever using a long double type, one needs to be careful about making > sure the algorithms work, and the tests pass (so have reasonable > tolerances), even when the long double type happens to be just the same > as double. This is the case on aarch64, and macOS/aarch64 is one of the > platforms where packages have to work, anyway, so this shouldn't be too > limiting anymore - but really one needs to test on such platform. > > R itself has an option to disable use of long double to make such > testing in R itself possible also on other platforms. In principle one > could do something similar in a package, have some ifdefs to disable > long doubles, but this is not required. And I probably wouldn't do that, > I'd just test on aarch64 regularly. > > See Writing R Extensions for more details. > > Best > Tomas > >> Apologies if this does not make much sense. >> >> Tim >> >> >> >> On Wed, 30 Apr 2025, at 9:33 AM, Uwe Ligges wrote: >>> On 30.04.2025 10:25, Tim Taylor wrote: >>>> Is it correct to say that R's conditional use of long double is around >>>> ensuring things work on platforms which have 'long double' identical to >>>> 'double' types, as opposed to there being an odd compiler targeted that >>>> does not even have any concept of 'long double' type? >>> a double is 64 bit and stored that way on all platforms, the concept of >>> long doubles is CPU specific. x86 chips have 80bit in the floating point >>> units for calculations before rounding (and normalizing) to a regular >>> double. >>> >>> Some chips, e.g. those ARM chips used in current M[123]Macs (hence very >>> relevant topic), do not support long doubles. And compilers offer to >>> compile without support for long doubles which e.g. CRAN uses to check >>> in an additional (issues) check. >>> >>> Best, >>> Uwe Ligges >>> >>>> As background this was motivated by a query raised in the matrixStats >>>> package: >>>> https://github.com/HenrikBengtsson/matrixStats/issues/278 >>>> >>>> ______________________________________________ >>>> R-package-devel@r-project.org mailing list >>>> https://stat.ethz.ch/mailman/listinfo/r-package-devel >>> >>> Attachments: >>> * smime.p7s >> ______________________________________________ >> R-package-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-package-devel ______________________________________________ R-package-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-package-devel
