Multiplicative Suborder Sord(a, n)

Here are some notes from my program XICalc - Extra Precision Integer Calculator http://www.oocities.org/hjsmithh/download.html#XICalc :

The multiplicative suborder function Sord(a, n) is the minimum positive integer e for which a^e == +/−1 mod n, or zero if no e exists. If a or n is less than 2, zero is returned.

e = Sord(a, n) // e = Multiplicative Suborder
// multiplicative suborder of base a (mod n) or zero if it does not exist.
// From Stephen Wolfram, Algebraic Properties of Cellular Automata (1984).
// Sord = Mord or Mord/2, Mord/2 iff a^(Mord/2) mod n = -1
{
  e = Mord(a, n)
  if ((e is odd) or e == 0), return
  e = e/2
  g1 = a^e mod n
  if (g1 != (n-1)) e = 2*e
}