Data commit

Task/Miller-Rabin-primality-test/Kotlin/miller-rabin-primality-test.kotlin

@@ -0,0 +1,53 @@
+// version 1.1.2
+
+import java.math.BigInteger
+import java.util.Random
+
+val bigTwo = BigInteger.valueOf(2L)
+
+fun isProbablyPrime(n: BigInteger, k: Int): Boolean {
+    require (n > bigTwo && n % bigTwo == BigInteger.ONE) { "Must be odd and greater than 2" }
+    var s = 0
+    val nn = n - BigInteger.ONE
+    var d: BigInteger
+    do {
+        s++
+        d = nn.shiftRight(s)
+    }
+    while (d % bigTwo == BigInteger.ZERO)
+
+    val rand = Random()
+    loop@ for (i in 1..k) {
+        var a: BigInteger
+        do {
+            a = BigInteger(n.bitLength(), rand)
+        }
+        while(a < bigTwo || a > nn) // make sure it's in the interval [2, n - 1]
+
+        var x = a.modPow(d, n)
+        if (x == BigInteger.ONE || x == nn) continue
+        for (r in 1 until s) {
+            x =  (x * x) % n
+            if (x == BigInteger.ONE) return false
+            if (x == nn) break@loop
+        }
+        return false
+    }
+    return true
+}
+
+fun main(args: Array<String>) {
+    val k = 20 // say
+    // obtain all primes up to 100
+    println("The following numbers less than 100 are prime:")
+    for (i in 3..99 step 2)
+        if (isProbablyPrime(BigInteger.valueOf(i.toLong()), k)) print("$i ")
+    println("\n")
+    // check if some big numbers are probably prime
+    val bia = arrayOf(
+        BigInteger("4547337172376300111955330758342147474062293202868155909489"),
+        BigInteger("4547337172376300111955330758342147474062293202868155909393")
+    )
+    for (bi in bia)
+        println("$bi is ${if (isProbablyPrime(bi, k)) "probably prime" else "composite"}")
+}