Unexpected result of fuzzy_eq() on large number

[ILyoan]

fuzzy_eq() is well working with small float numbers but when the number become too large that even the round-off error exceed the epsilon(default is 1e-6), the function can return an unexpected result.

See this
https://gist.github.com/ILyoan/5136141
fuzzy_eq() in 21th line will return false because
27272727272727276822 = 1e20 * (1/11) * 3
27272727272727272406 = 1e20 * (3/11)
and the difference between two numbers is larger than default epsilon

How about we use relative error method like this
https://gist.github.com/ILyoan/5136153

[lifthrasiir]

We can also use an ulp-based approach, like Google's C++ testing framework.

[metajack]

nominating production ready

[graydon]

accepted for production-ready milestone