Generally speaking, a value of double is not always representable
when demoted to a float. ISO C defines what to do when such
conversion loses precision, but leaves it undefined when the
value is completely out of range. (cf: ISO/IEC 9899:1990 section
6.2.1.4).

Because ruby do not have half-precision floating-point types this
is not a frequent headache but for pack / unpack, there are
specifiers that has something to do with C float types.  We have
to explicitly care these situations.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65768 b2dd03c8-39d4-4d8f-98ff-823fe69b080e