Pisano period: Difference between revisions

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@@ Line 71: / Line 71: @@
 }
+// OK for 'small' numbers.
-// Not particularly efficient but suffices here.
 func isPrime(n uint) bool {
-    if n%2 == 0 {
+    switch {
+    case n < 2:
+        return false
+    case n%2 == 0:
         return n == 2
-    }
+    case n%3 == 0:
-    if n%3 == 0 {
         return n == 3
-    }
+    default:
-    primes := getPrimes(n)
+        d := uint(5)
-    if len(primes) == 1 && primes[0] == n {
+        for d*d <= n {
+            if n%d == 0 {
+                return false
+            }
+            d += 2
+            if n%d == 0 {
+                return false
+            }
+            d += 4
+        }
         return true
     }
-    return false
 }