Generated table in table_driven() should be memorized

[hugolbz]

I tried to used the table_driven algorithm from python, and quickly realized that the generated table was not memorized. Instead it is generated for each single call to table_driven(), making the computation several order of magnitude slower than bit_by_bit_fast() in my case.

I think the table should be memorized, either at init, or at first call to table_driven, with something like:

if self.tbl is None:
    self.tbl = self.gen_table()

[Ovsthus]

We are using this function in a tight loop at my company and this is some very low hanging fruit for optimizing performance.
By implementing this locally we see the computation time reduced by a factor of 6.

This would be very nice to see fixed upstream, is this something that can be done?

[tpircher]

This is now merged to main. Thank you for your contribution.