[pypy-dev] More strategies

[Armin Rigo]

Hi Antonio,

On Thu, Nov 14, 2013 at 2:35 PM, Antonio Cuni <anto.cuni at gmail.com> wrote:
> W_FloatObjectPresevingTheBits will be created only by operations like
> struct.unpack, cffi.cast, etc.

That's not enough: if you read one such float into a variable and then
append that variable into another list, then the other list also needs
to record the fact that it contains special NaNs.

It seems we could pick the following solution instead: keep
FloatStrategy, storing a RPython list of floats --- including possibly
special NaNs; and add FloatIntStrategy, which cannot store special
NaNs.  We check for the special NaNs when we add into a
FloatIntStrategy list, and when converting from FloatStrategy to
FloatIntStrategy.  For the latter case we do indeed need to check all
items, which sounds a bit pointless, but (1) this is already a good
progress over the current situation, which is that we need to allocate
a W_FloatObject per item and a new RPython list to hold them; and (2)
doing the check over all items upon conversion is actually the same
total amount of work as it would be if we checked each item as it was
added to the FloatStrategy list.

(Fwiw, I'm also fond of the idea that it should actually be a
"FloatIntNoneStrategy"; it would improve the situation even for lists
of int-or-None.)


A bientôt,

Armin.