Data commit

Task/Miller-Rabin-primality-test/Swift/miller-rabin-primality-test.swift

@@ -0,0 +1,37 @@
+import BigInt
+
+private let numTrails = 5
+
+func isPrime(_ n: BigInt) -> Bool {
+  guard n >= 2 else { fatalError() }
+  guard n != 2 else { return true }
+  guard n % 2 != 0 else { return false }
+
+  var s = 0
+  var d = n - 1
+
+  while true {
+    let (quo, rem) = (d / 2, d % 2)
+
+    guard rem != 1 else { break }
+
+    s += 1
+    d = quo
+  }
+
+  func tryComposite(_ a: BigInt) -> Bool {
+    guard a.power(d, modulus: n) != 1 else { return false }
+
+    for i in 0..<s where a.power((2 as BigInt).power(i) * d, modulus: n) == n - 1 {
+      return false
+    }
+
+    return true
+  }
+
+  for _ in 0..<numTrails where tryComposite(BigInt(BigUInt.randomInteger(lessThan: BigUInt(n)))) {
+    return false
+  }
+
+  return true
+}