signature of permutation

This scales more like linearly and doesn't seem to be slower
on shorter lists. I think it's better than the first one
I posted.

SignaturePermutation(inp) := block(
  [ n:length(inp), k, visited , p,  knext, L, sgn:1],
  visited : make_array(any,n),
  p : make_array(any,n),
  fillarray(p,inp),
  for k : 0 thru n-1 do (
    if not visited[k] then (
      knext : k,
      L : 0,
      while not visited[knext] do (
        L : L + 1,
        visited[knext] : true,
        knext : p[knext]-1 ),
      if evenp(L) then sgn : -sgn )),
  sgn);

-- John Lapeyre