How does Wc3 checks if 2 maps are the same ?

Public Function xorRotateStream(ByVal s As IO.Stream, Optional ByVal length As Integer = -1) As UInteger
If length = -1 Then length = CInt(s.Length)
Dim val As UInteger = 0
Dim r As New IO.BinaryReader(s)
For repeat As Integer = 1 To length - 3 Step 4
val = ShiftRotateLeft(val Xor r.ReadUInt32(), 3)
Next repeat
For repeat As Integer = 1 To length Mod 4
val = ShiftRotateLeft(val Xor CUInt(r.ReadByte()), 3)
Next repeat
Return val
End Function

Public Function xorRotateMap(ByVal mpqa As MPQ.Archive) As UInteger
Dim val As UInteger = 0
Dim backupMPQA As New MPQ.Archive(My.Settings.war3path + "Copy of War3Patch.mpq")

Dim ssj() As String = {"Scripts\common.j", "Scripts\blizzard.j"}
For Each s As String In ssj
Dim f As MPQ.FileStream
If mpqa.hashTable.contains(s) Then
f = New MPQ.FileStream(mpqa, s)
Else
f = New MPQ.FileStream(backupMPQA, s)
End If
val = val Xor xorRotateStream(f)
Next s
val = ShiftRotateLeft(val, 3)
val = ShiftRotateLeft(val Xor CUInt(&H3F1379E), 3)

Dim ss() As String = {"war3map.j", "scripts\war3map.j", "war3map.w3e", "war3map.wpm", "war3map.doo", "war3map.w3u", "war3map.w3b", "war3map.w3d", "war3map.w3a", "war3map.w3q"}
For Each s As String In ss
If mpqa.hashTable.contains(s) Then
Dim f As New MPQ.FileStream(mpqa, s)
val = ShiftRotateLeft(val Xor xorRotateStream(f), 3)
f.Close()
End If
Next s

Return val
End Function