I never said it was impossible, just very hard.
Le 17/01/2017 à 16:48, Stephan Houben a écrit : > Hi Xavier, > > In this bright age of IEEE-754 compatible CPUs, > it is certainly possible to achieve reproducible FP. > I worked for a company whose software produced bit-identical > results on various CPUs (x86, Sparc, Itanium) and OSes (Linux, > Solaris, Windows). > > The trick is to closely RTFM for your CPU and compiler, in particular > all those nice > appendices related to "FPU control words" and "FP consistency models". > > For example, if the author of that article had done so, he might have > learned > about the "precision control" field of the x87 status register, which > you can set > so that all intermediate operations are always represented as 64-bits > doubles. > So no double roundings from double-extended precision. > > (Incidentally, the x87-internal double-extended precision is another > fine example where > being "more precise on occasion" usually does not help.) > > Frankly not very impressed with that article. > I could go in detail but that's off-topic, and I will try to fight > the "somebody is *wrong* on the Internet" urge. > > Stephan > > 2017-01-17 16:04 GMT+01:00 Xavier Combelle <xavier.combe...@gmail.com > <mailto:xavier.combe...@gmail.com>>: > > >> Generally speaking, there are two reasons why people may *not* >> want an FMA operation. >> 1. They need their results to be reproducible across >> compilers/platforms. (the most common reason) >> > The reproducibility of floating point calculation is very hard to > reach a good survey of the problem is > https://randomascii.wordpress.com/2013/07/16/floating-point-determinism/ > <https://randomascii.wordpress.com/2013/07/16/floating-point-determinism/> > it mention the fma problem but it only a part of a biggest picture > > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org <mailto:Python-ideas@python.org> > https://mail.python.org/mailman/listinfo/python-ideas > <https://mail.python.org/mailman/listinfo/python-ideas> > Code of Conduct: http://python.org/psf/codeofconduct/ > <http://python.org/psf/codeofconduct/> > >
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