dangerous float operations

While implementing storage of price/cost/balance in cents I've stumbled upon one nasty bug. Consider the following code:

class Account < ActiveRecord::Base
def balance=(amount)
  write_attribute(:balance, amount.to_f*100.0)
end
end

(analogous accessor code omitted)

It works as expected... usually. That is, there's one magical number - 4.6 - which sets the field balance not to 460, but to 459, thus screwing up the whole purpose of this.

4.6 is the only magical number I could find - others work like charm and expected.

In Ruby (not on Rails) works as expected:

class Act
  def balance=(amount)
    @balance = amount.to_f*100
  end
end

that is, for 4.6 works like for all the other numbers.

EDIT: This problem seems to be related to to_i method called on floats. AND it seems to be Ruby-related

irb(main):005:0> (895.0).to_i
=> 895
irb(main):006:0> (8.95*100).to_i
=> 894

(yes, I've just discovered that to_i just cuts away everything after the point)

Workaround: add a tiny number to the converted one OR use .round

irb(main):007:0> (8.95*100 + 0.0000001).to_i
=> 895
irb(main):007:0> (8.95*100).round
=> 895

Proposed solution: make field accessors for integer fields use .round instead of to_i.

As for now, I'm good with adding .round in my custom accessor.