The authoritative source in Linux is the code and always has been.
Clearly document system behavior or code is essentially useless.
The random char device code isn't that hard to understand, and if you're not a strong C programmer (the Ruby-core people are good C programmers, I suppose) - there's a paper explaining how it works: https://eprint.iacr.org/2012/251.pdf
Aaron
According to this documentation:
http://ruby-doc.org/core-2.1.2/Float.html#method-i-round
How do you explain?
2.1.2 :011 > 15.round(-1) => 20