how to manage swift3 i-- loop

swift 2:
for(var i=m;i<n;i++){}
swift 3:
for i in m..<n {}

swift 2:
for(var i=n;i>m;i--){}
swift 3:
if(n > m){
  for k in m ..< n {
    i = m+n-k
    ...
}
}