MurMurHash3

Class Murmur3
    ' 128 bit output, 64 bit platform version

    Public Shared READ_SIZE As ULong = 16
    Private Shared C1 As ULong = &H87c37b91114253d5UL
    Private Shared C2 As ULong = &H4cf5ad432745937fL

    Private length As ULong
    Private seed As UInteger
    ' if want to start with a seed, create a constructor
    Private h1 As ULong
    Private h2 As ULong

    Private Sub MixBody(k1 As ULong, k2 As ULong)
        h1 = h1 Xor MixKey1(k1)

        h1 = h1.RotateLeft(27)
        h1 += h2
        h1 = h1 * 5 + &H52dce729

        h2 = h2 Xor MixKey2(k2)

        h2 = h2.RotateLeft(31)
        h2 += h1
        h2 = h2 * 5 + &H38495ab5
    End Sub

    Private Shared Function MixKey1(k1 As ULong) As ULong
        k1 *= C1
        k1 = k1.RotateLeft(31)
        k1 *= C2
        Return k1
    End Function

    Private Shared Function MixKey2(k2 As ULong) As ULong
        k2 *= C2
        k2 = k2.RotateLeft(33)
        k2 *= C1
        Return k2
    End Function

    Private Shared Function MixFinal(k As ULong) As ULong
        ' avalanche bits

        k = k Xor k >> 33
        k *= &Hff51afd7ed558ccdUL
        k = k Xor k >> 33
        k *= &Hc4ceb9fe1a85ec53UL
        k = k Xor k >> 33
        Return k
    End Function

    Public Function ComputeHash(bb As Byte()) As Byte()
        ProcessBytes(bb)
        Return Hash
    End Function

    Private Sub ProcessBytes(bb As Byte())
        h1 = seed
        Me.length = 0L

        Dim pos As Integer = 0
        Dim remaining As ULong = CULng(bb.Length)

        ' read 128 bits, 16 bytes, 2 longs in eacy cycle
        While remaining >= READ_SIZE
            Dim k1 As ULong = bb.GetUInt64(pos)
            pos += 8

            Dim k2 As ULong = bb.GetUInt64(pos)
            pos += 8

            length += READ_SIZE
            remaining -= READ_SIZE

            MixBody(k1, k2)
        End While

        ' if the input MOD 16 != 0
        If remaining > 0 Then
            ProcessBytesRemaining(bb, remaining, pos)
        End If
    End Sub

    Private Sub ProcessBytesRemaining(bb As Byte(), remaining As ULong, pos As Integer)
        Dim k1 As ULong = 0
        Dim k2 As ULong = 0
        length += remaining

        ' little endian (x86) processing
        Select Case remaining
            Case 15
                k2 = k2 Xor CULng(bb(pos + 14)) << 48
                ' fall through
                goto case 14
            Case 14
                k2 = k2 Xor CULng(bb(pos + 13)) << 40
                ' fall through
                goto case 13
            Case 13
                k2 = k2 Xor CULng(bb(pos + 12)) << 32
                ' fall through
                goto case 12
            Case 12
                k2 = k2 Xor CULng(bb(pos + 11)) << 24
                ' fall through
                goto case 11
            Case 11
                k2 = k2 Xor CULng(bb(pos + 10)) << 16
                ' fall through
                goto case 10
            Case 10
                k2 = k2 Xor CULng(bb(pos + 9)) << 8
                ' fall through
                goto case 9
            Case 9
                k2 = k2 Xor CULng(bb(pos + 8))
                ' fall through
                goto case 8
            Case 8
                k1 = k1 Xor bb.GetUInt64(pos)
                Exit Select
            Case 7
                k1 = k1 Xor CULng(bb(pos + 6)) << 48
                ' fall through
                goto case 6
            Case 6
                k1 = k1 Xor CULng(bb(pos + 5)) << 40
                ' fall through
                goto case 5
            Case 5
                k1 = k1 Xor CULng(bb(pos + 4)) << 32
                ' fall through
                goto case 4
            Case 4
                k1 = k1 Xor CULng(bb(pos + 3)) << 24
                ' fall through
                goto case 3
            Case 3
                k1 = k1 Xor CULng(bb(pos + 2)) << 16
                ' fall through
                goto case 2
            Case 2
                k1 = k1 Xor CULng(bb(pos + 1)) << 8
                ' fall through
                goto case 1
            Case 1
                k1 = k1 Xor CULng(bb(pos))
                ' fall through
                Exit Select
            Case Else
                Throw New Exception("Something went wrong with remaining bytes calculation.")
        End Select

        h1 = h1 Xor MixKey1(k1)
        h2 = h2 Xor MixKey2(k2)
    End Sub

    Public ReadOnly Property Hash() As Byte()
        Get
            h1 = h1 Xor length
            h2 = h2 Xor length

            h1 += h2
            h2 += h1

            h1 = Murmur3.MixFinal(h1)
            h2 = Murmur3.MixFinal(h2)

            h1 += h2
            h2 += h1

            Dim hash__1 = New Byte(Murmur3.READ_SIZE - 1) {}

            Array.Copy(BitConverter.GetBytes(h1), 0, hash__1, 0, 8)
            Array.Copy(BitConverter.GetBytes(h2), 0, hash__1, 8, 8)

            Return hash__1
        End Get
    End Property
End Class