https://github.com/ruby/ruby/commit/b3b5e626ad69bf22be3228f8...
Linked commit contains code for rotating tagged floats so bits 60..62 go to the least significant positions, and a comment about a range of unboxed floats between 1.7...e-77 and 1.7...e77, plus special casing 0.0.
https://github.com/ruby/ruby/commit/b3b5e626ad69bf22be3228f8...