On Mon, Feb 7, 2022 at 12:31 PM Gregory P. Smith <g...@krypto.org> wrote:
> > > On Mon, Feb 7, 2022 at 11:06 AM Victor Stinner <vstin...@python.org> > wrote: > >> Hi Mark, >> >> Aha, good, you posted an email to python-dev, good :-) Last days, I >> was trying to collect more data about this topic, especially find >> platforms which *don't* support IEEE 754, before posting to >> python-dev. >> >> Nowadays, outside museums, it's hard to find computers which don't >> implement IEEE 754. >> >> * Since 1998, IBM S/390 supports IEEE 754. >> * Compaq/DEC VAX didn't use IEEE 754, but are no longer built since >> 2000 (you cant still use Python 3.10 if it can be built on it!) >> * Some Cray computers like Cray SV1 (1998) don't implement IEEE 754, >> but other Cray computers like Cray T90 (1995) implement IEEE 754. >> >> There are embedded devices with no hardware FPU: in this case, the FPU >> is implemented in software. I expect it to implement IEEE 754. Is >> CPython a good target for such small CPUs which have no hardware FPU? >> MicroPython may better fit their needs. >> >> On the other side, all moderns CPU architectures support IEEE 754: >> Intel x86, ARM, IBM Power and PowerPC, Compaq/DEC Alpha, HP PA-RISC, >> Motorola 68xxx and 88xxx, SGI R-xxxx, Sun SPARC. >> >> Sources: >> >> * >> https://en.wikipedia.org/wiki/Floating-point_arithmetic#IEEE_754:_floating_point_in_modern_computers >> * >> https://stackoverflow.com/questions/2234468/do-any-real-world-cpus-not-use-ieee-754 >> >> >> On Mon, Feb 7, 2022 at 7:25 PM Mark Dickinson <dicki...@gmail.com> wrote: >> > - Should we require the presence of NaNs in order for CPython to build? >> > - Should we require IEEE 754 floating-point for >> CPython-the-implementation? >> >> In the past, when we deprecated the support for an old platform, we >> didn't suddenly remove the code. We made sure that it's no longer >> possible to build on it. So if anyone notices, it's easy to revert >> (ex: remove the few lines in configure). >> >> Would it make sense to trigger a build error on plaforms which don't >> support IEEE 754 in Python 3.11, and later decide if it's time to >> remove the code in in Python 3.12? >> >> Well. If you ask *me*, I'm in favor of removing the code right now. If >> someone needs to support a platform which doesn't support IEEE 754, >> the support can be maintained *outside* the Python source code, as >> external patches or as a Git fork, no? >> >> Honestly, I never got access to any machine which doesn't support IEEE >> 754 (or nobody told me!). >> >> >> > - Should we require IEEE 754 floating-point for Python-the-language? >> >> Right now, I have no opinion on this question. >> >> >> > Note that on the current main branch there's a Py_NO_NAN macro that >> builders can define to indicate that NaNs aren't supported, but the Python >> build is currently broken if Py_NO_NAN is defined (see >> https://bugs.python.org/issue46656). If the answer to the first question >> is "No", then we need to fix the build under Py_NO_NAN. That's not a big >> deal - perhaps a couple of hours of work. >> >> My comment on bpo-46656: "Python uses Py_NAN without "#ifdef Py_NAN" >> guard since 2008. Building Python with Py_NO_NAN never worked. Nobody >> reported such build failure in the last 14 years..." >> >> If anyone would try building/using Python on a platform without NAN, I >> would expect that we would get a bug report or an email. I'm not aware >> of anything like that, so it seems like nobody uses Python on such >> platform. >> >> Victor >> > > It's 2022. We should just require both NaN and IEEE-754. > > By the time a system is large enough to build and run CPython, it is > exceedingly unlikely that it will not be able to do that. Even if it means > software emulation of IEEE-754 floating point on something large yet odd > enough not to have a FPU. > > The places where non-IEEE-754 and non-NaN floating point are likely to > exist are in specialized parallelized coprocessor hardware. Not the general > purpose CPU running CPython. > Do we have a buildbot that has a CPU or OS that can't handle IEEE-754? What are the chances we will get one? If the answers are "none" and "slim", then it seems reasonable to require NaN and IEEE-754.
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