Re: Is signed zero always available?

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From	Grant Edwards <grant.b.edwards@gmail.com>
Newsgroups	comp.lang.python
Subject	Re: Is signed zero always available?
Date	Wed, 22 Jun 2016 14:59:48 +0000 (UTC)
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On 2016-06-22, Random832 <random832@fastmail.com> wrote:
> On Wed, Jun 22, 2016, at 10:19, Grant Edwards wrote:
>
>> Is that guaranteed by Python, or just a side-effect of the
>> implementation?  Back in the days when Python used native C
>> integers I think the latter.
>
> AIUI, native C integers have never reliably supported signed zero
> even with representations that naively seem to have it. There's no
> well-defined way to detect it - no int version of copysign, for
> instance - and implementations are free to erase the distinction on
> every load/store or define one of them to be a trap representation.

It's been almost 25 years since I used hardware that supported signed
zero integers (CDC 6600).  I don't recall there being a C compiler
available.  We used Pascal and assembly, though I think FORTRAN was
what most people used.  I don't recall whether the Pascal
implementation exposed the existence of -0 to the user or not.

I'm pretty certain there wasn't a Python implementation...

-- 
Grant Edwards               grant.b.edwards        Yow! Loni Anderson's hair
                                  at               should be LEGALIZED!!
                              gmail.com

Thread

Is signed zero always available? Steven D'Aprano <steve@pearwood.info> - 2016-06-22 23:27 +1000
  Re: Is signed zero always available? Grant Edwards <grant.b.edwards@gmail.com> - 2016-06-22 14:19 +0000
  Re: Is signed zero always available? Random832 <random832@fastmail.com> - 2016-06-22 10:34 -0400
  Re: Is signed zero always available? Grant Edwards <grant.b.edwards@gmail.com> - 2016-06-22 14:59 +0000
  Re: Is signed zero always available? Christopher Reimer <christopher_reimer@icloud.com> - 2016-06-22 15:50 -0700
    Re: Is signed zero always available? Steven D'Aprano <steve@pearwood.info> - 2016-06-23 11:16 +1000
  Re: Is signed zero always available? Michael Selik <michael.selik@gmail.com> - 2016-06-23 00:34 +0000
  Re: Is signed zero always available? Grant Edwards <grant.b.edwards@gmail.com> - 2016-06-23 02:48 +0000

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