Ruby float precision

Question

As I understand it, Ruby (1.9.2) floats have a precision of 15 decimal digits. Therefore, I would expect rounding float x to 15 decimal places would equal x

Answer 1

Well, though I'm not certain on the details of how Ruby handles floats internally, I do know why this particular bit of code is failing on my box:

 > x = (0.33 * 10)
=> 3.3000000000000003
 > x.round(15)
=> 3.300000000000001

The first float keeps 16 decimal places for a total of 17 digits, for whatever reason. So, rounding to 15 discards those digits.