On Wed, Jun 22, 2016 at 4:53 PM Christopher Reimer < christopher_rei...@icloud.com> wrote:
> > On Jun 22, 2016, at 7:59 AM, Grant Edwards <grant.b.edwa...@gmail.com> > wrote: > > > >> On 2016-06-22, Random832 <random...@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. > > When I took mathematics in college, the following was true: > > -1 * 0 = 0 > > I would probably have gotten rapped on the knuckles by my instructors if I > answered -0. Zero was zero. No plus or minus about that. No discussion of > signed integers ever mentioned signed zero. > > Did I miss something in college? > I can't remember where I came across the concept. It might have been in calculus. Zero can be thought of as the asymptotic value of 1/n as n approaches infinity. If so, then negative zero would be the asymptote of -1/n as n approaches infinity. -- https://mail.python.org/mailman/listinfo/python-list