Keskustelu: Koodit: VB.NET: Onko alkuluku

Private Function TestIfPrime(ByVal A As Long) As Boolean
       'Fermat's little theorem
       ' if k^(A-1) mod A is not 1 then A is not a prime
       Dim i As Integer
       'check small primes
       If ((A Mod 2) = 0) And A <> 2 Then
           TestIfPrime = False
           Exit Function
       End If
       For i = 3 To 13 Step 2
           If ((A Mod i) = 0) And A <> i Then
               TestIfPrime = False
               Exit Function
           End If
       Next i

       'first 100 prime numbers as k's
       Dim pri() As Long = {0, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 113, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 179, 181, 191, 193, 197, 199, 211, 223, 227, 229, 233, 239, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 313, 317, 331, 337, 347, 349, 353, 359, 367, 373, 379, 383, 389, 397, 401, 409, 419, 421, 431, 433, 439, 443, 449, 457, 461, 463, 467, 479, 487, 491, 499, 503, 509, 521, 523, 541}
       Dim P As Long

       Dim c As Integer = UBound(pri)
       P = A - 1
       For i = 1 To c
           If A = pri(i) Then
               TestIfPrime = True
               Exit Function
           End If
           If Power_mod_N(pri(i), P, A) <> 1 Then
               TestIfPrime = False
               Exit Function
           End If
       Next i
       TestIfPrime = True
   End Function

Private Function Power_mod_N(ByVal P As Long, ByVal d As Long, ByVal n As Long) As Long
        'A = (P ^ D) Mod N , P must be less than N
        'A = (P^e2 * P^e2 * P^e3) Mod N where D= 2*e2+e3 , e3 is 1 or 0
        'A = ((P^e2)mod N) * ((P^e2)mod N)) * ((P^e3)mod N))Mod N
        'then recursive call untill exponent is one
        ' because P<N then P^1 mod N = P
        Dim e2 As Long
        Dim e3 As Long
        Dim a2 As Long
        Dim a3 As Long
        Dim a4 As Decimal
        Dim a5 As Decimal
        Dim a6 As Decimal

        e2 = d \ 2
        e3 = d - 2 * e2

        If e2 = 1 Then 'recursion ends
            a2 = P
        Else
            a2 = Power_mod_N(P, e2, n)  'recursion continues
        End If

        If e3 = 1 Then
            a3 = P 'a3=P when e3=1
        Else
            a3 = 1 ' P^0
        End If

        'A= (a2*a2*a3) mod N
        'A=((a2*a2)mod n * a3 )mod n
        a6 = CDec(a2) ' convert to decimal
        a4 = a6 * a6
        a5 = a4 Mod CDec(n)
        a4 = a5 * CDec(a3)
        Power_mod_N = CLng(a4 Mod CDec(n))
    End Function

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        'pienimmästä ylöspäin
        Dim i As Long
        Dim count As Long = 1
        Dim ts As TimeSpan
        Dim t1 As Date
        Dim t2 As Date
        TextBox1.Text = "Alhaalta ylös 100 000 lukua"
        TextBox3.Text = ""
        t2 = Now
        For i = 3 To 100000 Step 2
            If TestIfPrime(i) Then
                count = count + 1
                TextBox2.Text = CStr(count)
                Application.DoEvents()
            End If
        Next i
        t1 = Now
        ts = t1.Subtract(t2)
        TextBox3.Text = CStr(Int(i / ts.TotalSeconds)) + " lukua sekunnissa"

    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        'suurimmasta alaspäin testi
        Dim i As Long
        Dim count As Long = 1
        Dim ts As TimeSpan
        Dim t1 As Date
        Dim t2 As Date
        Dim m As Long

        TextBox1.Text = "Ylhäältä alas 100 000 lukua"
        TextBox3.Text = ""
        t2 = Now
        For i = 2 To 100000 Step 2
            m = 281474976710677 - CLng(i) 'suurimmasta alaspäin
            If TestIfPrime(m) Then
                count = count + 1
                TextBox2.Text = CStr(count)
            End If
            Application.DoEvents()
        Next i
        t1 = Now
        ts = t1.Subtract(t2)
        TextBox3.Text = CStr(Int(i / ts.TotalSeconds)) + " lukua sekunnissa"
    End Sub