math.c: more accuracy
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57779 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
math.c: more accuracy
[ruby-core:79907] [Bug #13279]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57779 b2dd03c8-39d4-4d8f-98ff-823fe69b080e