What is the best way to check if bits in two bitArrays are identical?

Question

I often need to compare two bit arrays to see if they are identical or not, so I came with a function that doesn't look too performant to me, seems like it could be better since there are three logical operations in a single line. I'm wonder if it's posible to simplify it.

Public Overloads Shared Function AreEqual(ByVal ba1 As BitArray, ByVal ba2 As BitArray) As Boolean

    If ba1.Length <> ba2.Length Then
        Return False
    End If

    Dim i As Integer
    For i = 0 To ba1.Length - 1
        If Not (Not ba1(i)) Xor ba2(i) Then
            Return False
        End If
    Next
    Return True

End Function

Edit:

After hours of testing and brainstorming, I came to my initial thoughts to reduce somehow the number of those three logical operators, and I put one of them into a variable, which means a single action to revert all bits at once instead of reverting bit by bit. This is the result, and is way much faster than previous one, about 3 times faster:

Public Overloads Shared Function AreEqual(ByVal ba1 As BitArray, ByVal ba2 As BitArray) As Boolean

    If ba1.Count <> ba2.Count Then
        Return False
    End If

    Dim revBa1 As BitArray = ba1.Not ' <<
    Dim i As Integer

    For i = 0 To ba1.Count - 1
        If (Not revBa1(i)) Xor ba2(i) Then ' eliminates one logical operation existing here before
            Return False
        End If
    Next
    Return True

End Function

Now, faster than this one? :) Who knows, maybe...

Edit 2:

After some more testing and unconclusive results I noticed that the second version of the function is incorrect. Although it gets the right result, but it changes the ba1 value like it were passed byRef to the function:

'------------------------
'ba1 before = 000000000000000000000000000000001
'ba2 before = 000000000000000000000000000000001
'ba1 after = 111111111111111111111111111111110
'ba2 after = 000000000000000000000000000000001
'function result = True
'------------------------

Any ideas?

Edit 3: The solution was simple, but the function isn't fast anymore:

Dim revBa1 As New BitArray(ba1)
    revBa1 = revBa1.Not()

Edit 4: Yes, this is it:

Public Overloads Shared Function AreEqual(ByVal ba1 As BitArray, ByVal ba2 As BitArray) As Boolean

    If ba1 Is Nothing OrElse ba2 Is Nothing Then
        Return False
    End If

    If ba1.Count <> ba2.Count Then
        Return False
    End If

    Dim i As Integer
    For i = 0 To ba1.Count - 1
        If ba1(i) Xor ba2(i) Then
            Return False
        End If
    Next
    Return True

End Function

I guess sometimes we don't see the forest because of trees :)

Answer 1

ba1(i) and ba2(i) return Booleans that can be compared directly:

Function AreEqual(ba1 As BitArray, ba2 As BitArray) As Boolean

    If ba1.Count <> ba2.Count Then Return False

    For i = 0 To ba1.Count - 1
        If ba1(i) <> ba2(i) Then Return False
    Next

    Return True
End Function

---

BitArray uses Integer array to store the bits, so for bigger BitArray (maybe about 100 bits? you might have to test that) it might be a bit faster to copy them to integer array before comparing:

Function AreEqual(ba1 As BitArray, ba2 As BitArray) As Boolean

    If ba1.Count <> ba2.Count Then Return False

    If ba1.Count < 64 Then                    ' needs some testing to determine this number
        For i = 0 To ba1.Count - 1
            If ba1(i) <> ba2(i) Then Return False
        Next
    Else
        Dim a1 = New Integer((ba1.Length - 1) \ 32) {}
        Dim a2 = New Integer((ba2.Length - 1) \ 32) {}

        ba1.CopyTo(a1, 0)
        ba2.CopyTo(a2, 0)

        For i = 0 To a1.Length - 1
            If a1(i) <> a2(i) Then Return False
        Next
    End If

    Return True
End Function

---

As a side note, shorter and slower way to compare enumerable collections is SequenceEquals:

Function AreEqual(ba1 As BitArray, ba2 As BitArray) As Boolean
    Return ba1.Cast(Of Boolean).SequenceEqual(ba2.Cast(Of Boolean))
End Function