Paul Ramsey <pram...@cleverelephant.ca> writes: > Mats, what ever happened to: > > https://github.com/libgeos/geos/pull/40 > > I'm just coming up against some stuff in the JTS commit log that expects > double double and I see you've done this work already some years ago, but > it's not committed that I can see. JTS changed over some code to use DD > exclusively about a year ago, so this is a case where porting has caught up > to need. > > Were there any substantial problems w/ your PR? If not I'm "just" going to > try and rebase it and use it as the basis for going ahead. > > (It seems like the state-of-the-art would eventually be to use the "long > double" type, which has an implementation in GCC, but does not yet have one > in clang, in hopes that by being close to the metal we'd eventually also > start to reap performance gains as the silicon adds instructions to improve > long double calculations. ???)
I don't follow this last paragraph. As I understand it, long double is a type defined by C that can be more precise than double, but doesn't have to be, and on x86 is typically 80 bits. double double is a technique to use two doubles to get roughly twice the precision. I would expect that on many CPUs, long double is the same as double. So double double is far more precise than long double always. https://en.wikipedia.org/wiki/Long_double https://en.wikipedia.org/wiki/Quadruple-precision_floating-point_format#Double-double_arithmetic _______________________________________________ geos-devel mailing list geos-devel@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/geos-devel