September 2017 Update

Task/CRC-32/Visual-Basic-.NET/crc-32-1.visual

@@ -0,0 +1,29 @@
+Public Class Crc32
+
+    ' Table for pre-calculated values.
+    Shared table(255) As UInteger
+
+    ' Initialize table
+    Shared Sub New()
+        For i As UInteger = 0 To table.Length - 1
+            Dim te As UInteger = i ' table entry
+            For j As Integer = 0 To 7
+                If (te And 1) = 1 Then te = (te >> 1) Xor &HEDB88320UI Else te >>= 1
+            Next
+            table(i) = te
+        Next
+    End Sub
+
+    ' Return checksum calculation for Byte Array,
+    '  optionally resuming (used when breaking a large file into read-buffer-sized blocks).
+    ' Call with Init = False to continue calculation.
+    Public Shared Function cs(BA As Byte(), Optional Init As Boolean = True) As UInteger
+        Static crc As UInteger
+        If Init Then crc = UInteger.MaxValue
+        For Each b In BA
+            crc = (crc >> 8) Xor table((crc And &HFF) Xor b)
+        Next
+        Return Not crc
+    End Function
+
+End Class

Task/CRC-32/Visual-Basic-.NET/crc-32-2.visual

@@ -0,0 +1,23 @@
+    ' Returns a Byte Array from a string of ASCII characters.
+    Function Str2BA(Str As String) As Byte()
+        Return System.Text.Encoding.ASCII.GetBytes(Str)
+    End Function
+
+    ' Returns a Hex string from an UInteger, formatted to a number of digits,
+    '  adding leading zeros If necessary.
+    Function HexF(Value As UInteger, Digits As Integer) As String
+        HexF = Hex(Value)
+        If Len(HexF) < Digits Then HexF = StrDup(Digits - Len(HexF), "0") & HexF
+    End Function
+
+    ' Tests Crc32 class
+    Sub Test()
+        Dim Str As String = "The quick brown fox jumps over the lazy dog"
+        Debug.Print("Input = """ & Str & """")
+        ' Convert string to Byte Array, compute crc32, and display formatted result
+        Debug.Print("Crc32 = " & HexF(Crc32.cs(Str2BA(Str)), 8))
+        ' This next code demonstrates continuing a crc32 calculation when breaking the input
+        ' into pieces, such as processing a large file by a series of buffer reads.
+        Crc32.cs(Str2BA(Mid(Str, 1, 20)))
+        Debug.Print("Crc32 = " & HexF(Crc32.cs(Str2BA(Mid(Str, 21)), False), 8))
+    End Sub

Task/CRC-32/Visual-Basic-.NET/crc-32-3.visual

@@ -0,0 +1,3 @@
+Input = "The quick brown fox jumps over the lazy dog"
+Crc32 = 414FA339
+Crc32 = 414FA339