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

[Yury Selivanov]

Yury Selivanov added the comment:

> 
> Stefan Krah added the comment:
> 
> It's instructive to run ./python Modules/_decimal/tests/bench.py (Hit Ctrl-C after the first cdecimal result, 5 repetitions or so).
> 
> fastint2.patch speeds up floats enormously and slows down decimal by 6%.
> fastint_alt.patch slows down float *and* decimal (5% or so).
> 
> Overall the status quo isn't that bad, but I concede that float benchmarks like that are useful for PR.
> 

Thanks Stefan! I'll update my patch to include Serhiy's ideas. The fact that fastint_alt slows down floats *and* decimals is not acceptable.

I'm all for keeping cpython and ceval loop simple, but we should not pass on opportunities to improve some things in a significant way.

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