Makes sense, thanks! math.fma() it is. :) On Tue, Jan 17, 2017, 7:48 AM Stephan Houben <stephan...@gmail.com> wrote:
> 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>: > > > 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/ > it mention the fma problem but it only a part of a biggest picture > > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/ > > > _______________________________________________ > Python-ideas mailing list > Python-ideas@python.org > https://mail.python.org/mailman/listinfo/python-ideas > Code of Conduct: http://python.org/psf/codeofconduct/
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