VB.net Byte Array Search

Question

I am in the process of developing a simple virus scanner, and I was searching for speed improvements on the following function:

Public Function FindAInB(ByRef byteArrayA() As Byte, ByRef byteArrayB() As Byte) As Integer
    Dim startmatch As Integer = -1
    Dim offsetA As Integer = 0
    Dim offsetB As Integer = 0

    For offsetB = 0 To byteArrayB.Length - 1
        If byteArrayA(offsetA) = byteArrayB(offsetB) Then
            If startmatch = -1 AndAlso offsetB < byteArrayB.Length - 8 Then
                startmatch = offsetB
            End If
            offsetA += 1
            If offsetA = byteArrayA.Length Then
                Exit For
            End If
        Else
            offsetA = 0
            startmatch = -1
        End If
    Next
    Return startmatch
End Function

I need it to be turbo fast because it's searching for about 7800 byte arrays in a selected file's bytes. Kind of hard to explain but is there an alternative for the code above or a way to speed it up?

Thanks In Advance!

it all depends on what the data looks like. is it sorted or in random order? — Scott M.
– Scott M., Commented Feb 9, 2011 at 17:33
How large is the arrays - the array you are searching through and the array you are searching for, respectively ? — driis
– driis, Commented Feb 9, 2011 at 17:36
Well, strings() is an array of 7281 byte arrays (which are virus signatures), the array i'm searching through is a readAllBytes() of a selected file. searching is done in a do while loop. — Seif Shawkat
– Seif Shawkat, Commented Feb 9, 2011 at 17:45

LukeH · Accepted Answer · 2011-02-09 17:40:13Z

1

You should check out string search algorithms like Boyer-Moore.

Although you're not actually searching text, you are searching for strings of bytes within a larger string of bytes, so these type of algorithms could help out considerably.

answered Feb 9, 2011 at 17:40

LukeH

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5 Comments

Seif Shawkat Over a year ago

The problem is that i have to search for a sequence of bytes (that exist in an array) in an array of bytes

LukeH Over a year ago

@Seif: Yes, I know. These kind of algorithms can still help. Instead of searching for a small sequence of characters inside a big sequence of characters you're searching for a small sequence of bytes inside a big sequence of bytes. It's exactly the same thing in principle.

Seif Shawkat Over a year ago

Plus i'm trying to avoid loops that waste time

LukeH Over a year ago

@Seif: Well, the Wikipedia page describes the algorithm and has an example implementation in C. I suppose you'd need to translate that into VB.

Seif Shawkat Over a year ago

@luke: yes but how could that be implemented in byte array searching?

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