On Fri, Sep 11, 2020 at 11:19:05AM -1000, David Mertz wrote:
> On Fri, Sep 11, 2020 at 10:19 AM Guido van Rossum <[email protected]> wrote:
>
> > While one may argue that writing `1e1000` is not an "arithmetic
> > operation", certainly it's certainly not "casting strings to floats", and
> > it's the simeplest way of producing `inf` in a pinch (in theory it's not
> > portable, but I think "in a pinch" means you don't care about that).
I think that the only reason that could fail to produce inf is if your C
doubles aren't IEEE-754 binary64.
Are there any such platforms that are capable of building CPython but
don't support IEEE-754? Or has anyone tried building CPython using, for
example, posits instead?
> For 128-bit versions of Python you'd need 1e4933. For 256-bit, 1e78914.
> But those work fine on 32-bit or 64-bit also.
Are there any Pythons with 128-bit or 256-bit floats?
I've just tried Jython and IronPython, and got:
>>> sys.float_info.max_10_exp
308L
for both of them, which matches CPython.
Micropython doesn't seem to support sys.float_info, but testing suggests
that the floats are 64 bit too:
# Micropython 1.9, Python version 3.4
>>> 1e309
inf
If anyone is seriously worried about their Python supporting more than
64 bit floats, you can use 1e80000 which should give inf on any system
supporting IEEE-754 no matter what size floats you have. What it will do
on a posit or other non-IEEE-754 machine, I have no idea :-)
--
Steve
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