Author gregsmith
Recipients christian.heimes, gregsmith, loewis, mark.dickinson, rhettinger, sopoforic, tim.peters
Date 2009-10-24.01:56:06
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Message-id <1256349370.93.0.165380742655.issue1087418@psf.upfronthosting.co.za>
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Actually, my view for 3.x is this: I do agree hugely with the 'top
level' decision to only have one type that handles everything, and
obviously the easiest way to get there is to just use the existing long
type. However, though the rad-2^15 implementation of the 'long' type was
a fine thing for the 2.x python where it's only used for relatively
unusual cases, I think it's too inefficient to use as the primary
integer type, so I'm wondering if there's a plan to replace it with
something more efficient (thus rendering this particular issue irrelevant).

I did spend some time delving into python internals years ago, but
haven't really looked into 3.x, so bear with me. I am aware of the
following 'speed tweaks' in Python 2.x integers, aren't these lost now?

   (1) integers all same size, allocated from linked-list pool instead
of from malloc
   (2) 'add' and 'sub' byte codes do special check in interpreter core
to see if ints being added, and will go direct to PyInt_FromLong where
possible

It would seem to me that a more suitable implementation would be to
store numbers as 32*k-bit 2's complement integers; I've used this in C++
libraries. Compared to the rad-15 sign/magnitude approach, it may seem
trickier to do carries but in practice it's not that big a deal. It also
basically assumes you have a decently fast 64-bit operation to do
multiplies and divides with, which I think is now reasonable. This
implementation will be much easier to optimize for the (now) extremely
common case where numbers fit into 32 bits.
It could also be possible to store 'wee' integers in a special pool and
only use malloc for larger ones. 

I know there's a lot of code in that module, virtually all of which
would be affected by this. But isn't this type now a big performance
factor in 3.x?
History
Date User Action Args
2009-10-24 01:56:11gregsmithsetrecipients: + gregsmith, tim.peters, loewis, rhettinger, mark.dickinson, christian.heimes, sopoforic
2009-10-24 01:56:10gregsmithsetmessageid: <1256349370.93.0.165380742655.issue1087418@psf.upfronthosting.co.za>
2009-10-24 01:56:09gregsmithlinkissue1087418 messages
2009-10-24 01:56:07gregsmithcreate