Is signed zero always available?

[Grant Edwards]

On 2016-06-22, Random832 <random832 at 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...

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