Data commit

Task/Fibonacci-sequence/Visual-Basic-.NET/fibonacci-sequence-1.vb

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+Function Fib(ByVal n As Integer) As Decimal
+    Dim fib0, fib1, sum As Decimal
+    Dim i As Integer
+    fib0 = 0
+    fib1 = 1
+    For i = 1 To n
+        sum = fib0 + fib1
+        fib0 = fib1
+        fib1 = sum
+    Next
+    Fib = fib0
+End Function

Task/Fibonacci-sequence/Visual-Basic-.NET/fibonacci-sequence-2.vb

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+Function Seq(ByVal Term As Integer)
+        If Term < 2 Then Return Term
+        Return Seq(Term - 1) + Seq(Term - 2)
+End Function

Task/Fibonacci-sequence/Visual-Basic-.NET/fibonacci-sequence-3.vb

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+    Function FiboBig(ByVal n As Integer) As BigInteger
+        ' Fibonacci sequence with BigInteger
+        Dim fibn2, fibn1, fibn As BigInteger
+        Dim i As Integer
+        fibn = 0
+        fibn2 = 0
+        fibn1 = 1
+        If n = 0 Then
+            Return fibn2
+        ElseIf n = 1 Then
+            Return fibn1
+        ElseIf n >= 2 Then
+            For i = 2 To n
+                fibn = fibn2 + fibn1
+                fibn2 = fibn1
+                fibn1 = fibn
+            Next i
+            Return fibn
+        End If
+        Return 0
+    End Function 'FiboBig
+
+    Sub fibotest()
+        Dim i As Integer, s As String
+        i = 2000000  ' 2 millions
+        s = FiboBig(i).ToString
+        Console.WriteLine("fibo(" & i & ")=" & s & " - length=" & Len(s))
+    End Sub 'fibotest

Task/Fibonacci-sequence/Visual-Basic-.NET/fibonacci-sequence-4.vb

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+Imports System
+Imports System.Collections.Generic
+Imports BI = System.Numerics.BigInteger
+
+Module Module1
+
+    ' A sparse array of values calculated along the way
+    Dim sl As SortedList(Of Integer, BI) = New SortedList(Of Integer, BI)()
+
+    ' Square a BigInteger
+    Function sqr(ByVal n As BI) As BI
+        Return n * n
+    End Function
+
+    ' Helper routine for Fsl(). It adds an entry to the sorted list when necessary
+    Sub IfNec(n As Integer)
+        If Not sl.ContainsKey(n) Then sl.Add(n, Fsl(n))
+    End Sub
+
+    ' This routine is semi-recursive, but doesn't need to evaluate every number up to n.
+    ' Algorithm from here: http://www.maths.surrey.ac.uk/hosted-sites/R.Knott/Fibonacci/fibFormula.html#section3
+    Function Fsl(ByVal n As Integer) As BI
+        If n < 2 Then Return n
+        Dim n2 As Integer = n >> 1, pm As Integer = n2 + ((n And 1) << 1) - 1 : IfNec(n2) : IfNec(pm)
+        Return If(n2 > pm, (2 * sl(pm) + sl(n2)) * sl(n2), sqr(sl(n2)) + sqr(sl(pm)))
+    End Function
+
+    ' Conventional iteration method (not used here)
+    Function Fm(ByVal n As BI) As BI
+        If n < 2 Then Return n
+        Dim cur As BI = 0, pre As BI = 1
+        For i As Integer = 0 To n - 1
+            Dim sum As BI = cur + pre : pre = cur : cur = sum : Next : Return cur
+    End Function
+
+    Sub Main()
+        Dim vlen As Integer, num As Integer = 2_000_000, digs As Integer = 35
+        Dim sw As System.Diagnostics.Stopwatch = System.Diagnostics.Stopwatch.StartNew()
+        Dim v As BI = Fsl(num) : sw.[Stop]()
+        Console.Write("{0:n3} ms to calculate the {1:n0}th Fibonacci number, ", sw.Elapsed.TotalMilliseconds, num)
+        vlen = CInt(Math.Ceiling(BI.Log10(v))) : Console.WriteLine("number of digits is {0}", vlen)
+        If vlen < 10000 Then
+            sw.Restart() : Console.WriteLine(v) : sw.[Stop]()
+            Console.WriteLine("{0:n3} ms to write it to the console.", sw.Elapsed.TotalMilliseconds)
+        Else
+            Console.Write("partial: {0}...{1}", v / BI.Pow(10, vlen - digs), v Mod BI.Pow(10, digs))
+        End If
+    End Sub
+End Module