Hello Carl! On Mon, Nov 24, 2014 at 9:55 AM, Carl Kleffner <cmkleff...@gmail.com> wrote: > Hi K.Frank > > It's absolutely your (community) choice of course and fairly unproblematic > if you stay inside the mingw-w64 system. > > It is however incompatible for MSVC compatibility even in case you never > touch long doubles, as it affects double precision computation.
Yes,to clarify my earlier comments: It is correct that even if you use regular 64-bit doubles, the (x87-style) floating-point hardware will (in extended-precision mode) compute intermediate results with 80-bit precision as long as the computations stay in the floating-point registers, and only round them down to 64-bit doubles when they are written to memory. And yes, this can give different (almost always better) results than computing intermediate results with 64-bit precision. So, yes, this will be incompatible with (but generally better than) the Microsoft approach, even when only using doubles (i.e., not long doubles). > See > random-and-unexpected-exception-flt-divide-by-zero-and-exception-flt-invalid-operation.aspx > or https://github.com/numpy/numpy/issues/5194 . At least it is a matter of > documentation. > > I would like to ask you for an item in the mingw-w64 FAQ to explain the > difference between the settings and how to choose double precision instead > (linking CRT_fp8.o AFAIK) Yes, very reasonable. Whatever default behavior Kai & Co. choose for mingw-w64, it should of course be documented, and, if different than the Microsoft approach, that difference should be highlighted. And, of course, the end-user should be able to override the default behavior, whether it's me who wants 80-precision for intermediate results, or someone like yourself who has a use-case where 64-bit intermediate results are desired. (Don't get me wrong -- I do believe that there are legitimate use-cases for using 64-bit precision for intermediate results. I just think they're rare.) (I, of course, would vote for the default to be 80-bit long doubles with 80-bit precision for intermediate results based on my own experience, but, much more importantly, based on the recommendation of the experts such as Kahan. But I would also vote for giving the end-user properly documented mechanisms to override the default.) > Cheers, > > Carl Best. Happy Extended-Precision Floating-Point Hacking! K. Frank > ... > 2014-11-24 15:01 GMT+01:00 K. Frank <kfrank2...@gmail.com>: >> >> Hi Carl! >> >> I very much think that 80 bits should be the default for >> long doubles, even if Microsoft does differently. >> ... ------------------------------------------------------------------------------ Download BIRT iHub F-Type - The Free Enterprise-Grade BIRT Server from Actuate! Instantly Supercharge Your Business Reports and Dashboards with Interactivity, Sharing, Native Excel Exports, App Integration & more Get technology previously reserved for billion-dollar corporations, FREE http://pubads.g.doubleclick.net/gampad/clk?id=157005751&iu=/4140/ostg.clktrk _______________________________________________ Mingw-w64-public mailing list Mingw-w64-public@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/mingw-w64-public
