B4J Tutorial B4J Primes Benchmark

Sub Process_Globals

End Sub

Sub AppStart (Args() As String)
    #if debug
    Log("Never test performance in debug mode!!!")
    ExitApplication
    #End If
 
    Dim start As Long = DateTime.Now
 
    'Algorithm #1
    Dim counter As Int = GetAllPrimesLessThan1(20000000) '20,000,000
    'Algorithm #2
'    Dim counter As Int = GetAllPrimesLessThan2(200000000) '200,000,000
    Dim EndTime As Long = DateTime.Now
    Log($"number of primes: ${NumberFormat2(counter, 0, 0, 0, True)}"$)
    Log($"Time: $1.4{(EndTime - start) / 1000}"$)
End Sub

Private Sub GetAllPrimesLessThan1 (MaxPrime As Int) As Int
    Dim counter As Int
    For i = 2 To MaxPrime - 1
        If IsPrime(i) Then counter = counter + 1
    Next
    Return counter
End Sub

Private Sub IsPrime(Num As Int) As Boolean
    If Num <= 1 Then Return False
    If Num <= 3 Then Return True
    If ((Num Mod 2) = 0 Or (Num Mod 3) = 0) Then Return False
    For c = 5 To Sqrt(Num) Step 6
        If ((Num Mod c) = 0 Or Num Mod (c + 2) = 0) Then Return False
    Next
    Return True
End Sub

Private Sub GetAllPrimesLessThan2 (MaxPrime As Int) As Int
    Dim Count As Int = 0
    Dim MaxSquareRoot As Int = Sqrt(MaxPrime)
    Dim eliminated As B4XBitSet 'B4XCollections (collections implemented in B4A)
    eliminated.Initialize(MaxPrime + 1)
    For i = 2 To MaxPrime
        If eliminated.Get(i) = False Then
            Count = Count + 1
            If i <= MaxSquareRoot Then
                For j = i * i To MaxPrime Step i
                    eliminated.Set(j, True)
                Next
            End If
        End If
    Next
    Return Count
End Sub