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From: Christopher Reimer <christopher_reimer@icloud.com>
Newsgroups: comp.lang.python
Subject: Re: Is signed zero always available?
Date: Wed, 22 Jun 2016 15:50:59 -0700
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> On Jun 22, 2016, at 7:59 AM, Grant Edwards <grant.b.edwards@gmail.com> wro=
te:
>=20
>> On 2016-06-22, Random832 <random832@fastmail.com> wrote:
>>> On Wed, Jun 22, 2016, at 10:19, Grant Edwards wrote:
>>>=20
>>> 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.
>>=20
>> 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.
>=20
> 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.

When I took mathematics in college, the following was true:

-1 * 0 =3D 0

I would probably have gotten rapped on the knuckles by my instructors if I a=
nswered -0. Zero was zero. No plus or minus about that. No discussion of sig=
ned integers ever mentioned signed zero.

Did I miss something in college?

Or did -0 represent zero volts on the negative rail of an op-amp in electron=
ics?=20

Thank you,

Chris R.=