Hi Esteban, > It is not for printing but for testing. I want to assert that a > certain calculation gives the expected result. > And then it fails because of the difference above when it is > "semantically" correct.
If you want reliable precision tests with IEEE floats, you should use rounding to powers of 2, not 10. Round to 1/8 or 1/16, but not to 1/10. The fundamental issue is that 1/10 does not have an exact finite representation in base 2. No matter how I/O libraries handle the conversion between base 2 (in the binary representation of IEEE floats) and base 10 (in the text representation), there will always be bad surprises because the expectations we have from working in base 10 cannot all be met with an internal representation in base 2. So if your goal is not fundamentally related to I/O, forget about I/O and design your code to work the binary level, in particular for testing. However, if your problem specification explicitly requires precision guarantees in base 10 (which seems to be your case, from a quick glance at the Wikipedia page you cite), then it's best to avoid binary floats completely. Rationals (fractions) are one option, scaled integers another one. Konrad.
