[Python-3000] Math in Python 3.0

[Giovanni Bajo]

Tim Peters wrote:

> I do the same kind of thing all the time; e.g., here from the tail end
> of a hybrid modular/binary gcd function, which uses parity checks in
> three places:
>
>     # invariants:
>     # a > b >= 0
>     # a is odd
>     # b is odd or 0
>     while b:
>         a %= b
>         if a & 1:
>             a = b-a
>         assert a & 1 == 0
>         a >>= 1
>         if a:
>             while a & 1 == 0:
>                 a >>= 1
>         a, b = b, a
>
>     return a << nbits
>
> For a long time CPython took time proportional to the number of bits
> in n to compute n&1, so it wasn't actually efficient, but recent
> releases repaired that.  In any case the code is quite clear and
> directly to the point.

Since we're at it, do you have any idea on why Python is so slow when doing
such bit-full code?
See for instance
http://shootout.alioth.debian.org/debian/benchmark.php?test=nsievebits&lang=all,
where the Python version needs to play caching tricks to get some speed.
-- 
Giovanni Bajo