Ah, yeah I was trying to get a lay explanation of how arithmetic coding assuming it was done with enough precision wouldn't achieve the perfect security properties.
It might just be that the precision rapidly becomes unmanageable, because I guess you need to support the least probable symbol from every token without ever losing precision (normally arithmetic coders will re-normalize after each symbol to keep the accumulator in a reasonable precision, though they could be designed to do so as infrequently as you like at a performance cost)... If no renormalization is possible I guess an arithmetic coder accumulator would need to handle values like (1/least_prob_token)^n_tokens which gets extremely big extremely fast -- and would at the very least need an unconventional construction.
It might just be that the precision rapidly becomes unmanageable, because I guess you need to support the least probable symbol from every token without ever losing precision (normally arithmetic coders will re-normalize after each symbol to keep the accumulator in a reasonable precision, though they could be designed to do so as infrequently as you like at a performance cost)... If no renormalization is possible I guess an arithmetic coder accumulator would need to handle values like (1/least_prob_token)^n_tokens which gets extremely big extremely fast -- and would at the very least need an unconventional construction.