Kotlin implementation of Optimus integer hashing algorithm https://github.com/jenssegers/optimus

Optimus.kt

class Optimus(private val prime: Int,
			  private val randomNumber: Int,
			  private val modInverse: Int = ModInverse(prime))
{
	init
	{
		if (!isProbablyPrime(prime)) throw IllegalArgumentException("$prime is not a prime number")
	}

	fun encode(n: Int): Int = n * this.prime and MAX_INT xor this.randomNumber
	fun decode(n: Int): Int = (n xor this.randomNumber) * this.modInverse and MAX_INT

	companion object
	{
		private const val MAX_INT = Integer.MAX_VALUE

		private fun ModInverse(n: Int): Int
		{

			val p = BigInteger.valueOf(n.toLong())
			val l = java.lang.Long.valueOf(MAX_INT.toLong()) + 1L
			val m = BigInteger.valueOf(l)
			return p.modInverse(m).toInt()
		}

		private fun isProbablyPrime(n: Int): Boolean
		{
			return BigInteger.valueOf((n - 1).toLong()).nextProbablePrime() == BigInteger.valueOf(n.toLong())
		}
	}
}