math.c: optimization for Bignum
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49449 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
math.c: optimization for Bignum
direct conversion using rb_big2dbl(). [Feature #10800]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49449 b2dd03c8-39d4-4d8f-98ff-823fe69b080e