[issue21955] ceval.c: implement fast path for integers with a single digit

[Yury Selivanov]

Yury Selivanov added the comment:

> People should stop getting hung up about benchmarks numbers and instead should first think about what they are trying to *achieve*. FP performance in pure Python does not seem like an important goal in itself.

I'm not sure how to respond to that.  Every performance aspect *is* important.  numpy isn't shipped with CPython, not everyone uses it.  In one of my programs I used colorsys extensively -- did I need to rewrite it using numpy?  Probably I could, but that was a simple shell script without any dependencies.

It also harms Python 3 adoption a little bit, since many benchmarks are still slower.  Some of them are FP related.

In any case, I think that if we can optimize something - we should.


> Also, some benchmarks may show variations which are randomly correlated with a patch (e.g. before of different code placement by the compiler interfering with instruction cache wayness). 

30-50% speed improvement is not a variation.  It's just that a lot less code gets executed if we inline some operations.


> It is important not to block a patch because some random benchmark on some random machine shows an unexpected slowdown.

Nothing is blocked atm, we're just discussing various approaches.


> That said, both of Serhiy's patches are probably ok IMO.

Current Serhiy's patches are incomplete.  In any case, I've been doing some research and will post another message shortly.

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<http://bugs.python.org/issue21955>
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