[Python-Dev] Caching float(0.0)

[Nick Maclaren]

=?ISO-8859-1?Q?=22Martin_v=2E_L=F6wis=22?= <martin at v.loewis.de> wrote:
> 
> >> The total count of floating point numbers allocated at this point is 985794.
> >> Without the reuse, they would be 1317145, so this is a saving of 25%, and
> >> of 5Mb.
> > 
> > And, if you optimised just 0.0, you would get 60% of that saving at
> > a small fraction of the cost and considerably greater generality.
> 
> As Michael Hudson observed, this is difficult to implement, though:
> You can't distinguish between -0.0 and +0.0 easily, yet you should.

That was the point of a previous posting of mine in this thread :-(

You shouldn't, despite what IEEE 754 says, at least if you are
allowing for either portability or numeric validation.

There are a huge number of good reasons why IEEE 754 signed zeroes
fit extremely badly into any normal programming language and are
seriously incompatible with numeric validation, but Python adds more.
Is there any other type where there are two values that are required
to be different, but where both the hash is required to be zero and
both are required to evaluate to False in truth value context?


Regards,
Nick Maclaren,
University of Cambridge Computing Service,
New Museums Site, Pembroke Street, Cambridge CB2 3QH, England.
Email:  nmm1 at cam.ac.uk
Tel.:  +44 1223 334761    Fax:  +44 1223 334679