Data commit

Task/Long-primes/Visual-Basic-.NET/long-primes.vb

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+Imports System, System.Collections.Generic, System.Linq, System.Console
+
+Module LongPrimes
+
+    Function Period(ByVal n As Integer) As Integer
+        Dim m As Integer, r As Integer = 1
+        For i As Integer = 0 To n : r = 10 * r Mod n : Next
+        m = r : Period = 1 : While True
+            r = (10 * r) Mod n : If r = m Then Return Period
+            Period += 1 : End While
+    End Function
+
+    Sub Main()
+        Dim primes As IEnumerable(Of Integer) = SomePrimeGenerator.Primes(64000).Skip(1).Where(Function(p) Period(p) = p - 1).Append(99999)
+        Dim count As Integer = 0, limit As Integer = 500
+        WriteLine(String.Join(" ", primes.TakeWhile(Function(p) p <= limit)))
+        For Each prime As Integer In primes
+            If prime > limit Then
+                WriteLine($"There are {count} long primes below {limit}")
+                limit <<= 1 : End If : count += 1 : Next
+    End Sub
+
+End Module
+
+Module SomePrimeGenerator
+
+    Iterator Function Primes(lim As Integer) As IEnumerable(Of Integer)
+        Dim flags As Boolean() = New Boolean(lim) {},
+            j As Integer = 2, d As Integer = 3, sq As Integer = 4
+        While sq <= lim
+            If Not flags(j) Then
+                Yield j : For k As Integer = sq To lim step j
+                    flags(k) = True : Next
+            End If : j += 1 : d += 2 : sq += d
+        End While : While j <= lim
+            If Not flags(j) Then Yield j
+            j += 1 : End While
+    End Function
+
+End Module