devxlogo

RLEUncompress – Uncompress data compressed using RLECompress

RLEUncompress – Uncompress data compressed using RLECompress

Private Declare Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (dest As _    Any, source As Any, ByVal Bytes As Long)' Uncompress a block of data compressed with RLECompress'' Returns TRUE if successful (this version either returns True or raises an ' error)'' ADDRESS points to the buffer that holds the compressed data'      use StrPtr(s) if it's a string, VarPtr(arr(0)) if it's an array' BYTES is the size of the compressed data'      use LenB(s) if it's a string, N * LenB(arr(0)) if it's an array' OUTBUFFER is an array of bytes that will receive the uncompressed dataFunction RLEUncompress(ByVal address As Long, ByVal Bytes As Long, _    outBuffer() As Byte) As Boolean    Dim ItemSize As Integer    Dim outBytes As Long    Dim inIndex As Long    Dim outIndex As Long    Dim i As Long    Dim prevValue As Currency    Dim currValue As Currency    Dim matchCount As Integer        ' get the signature, exit if not matching    CopyMemory ItemSize, ByVal address, 2    If ItemSize <> &HABCD Then        Err.Raise 5, , "This hasn't been compressed with RLECompress"    End If    ' get ItemSize, exit if invalid    CopyMemory ItemSize, ByVal address + 2, 2    If ItemSize <> 1 And ItemSize <> 2 And ItemSize <> 4 And ItemSize <> 8 Then        Err.Raise 5, , "Wrong value for ItemSize"    End If    ' get the length of the uncompressed data    CopyMemory outBytes, ByVal address + 4, 4        ' prepare the output buffer    ReDim outBuffer(0 To outBytes - 1) As Byte        ' get the first value    CopyMemory prevValue, ByVal address + 8, ItemSize    address = address + 8 + ItemSize    ' copy to the output buffer as-is    CopyMemory outBuffer(0), prevValue, ItemSize    outIndex = ItemSize        ' repeat until the output buffer is full    Do While outIndex < outBytes        ' get the next value from the input buffer        CopyMemory currValue, ByVal address, ItemSize        address = address + ItemSize        ' move to the output buffer        CopyMemory outBuffer(outIndex), currValue, ItemSize        outIndex = outIndex + ItemSize                If prevValue = currValue Then            ' two consecutive values are equal            ' extract the matchCount value            CopyMemory matchCount, ByVal address, 2            address = address + 2            ' replicate the value that number of times            For i = 3 To matchCount                ' move to the output buffer                CopyMemory outBuffer(outIndex), currValue, ItemSize                outIndex = outIndex + ItemSize            Next        Else            prevValue = currValue        End If    Loop        ' signal success    RLEUncompress = TrueEnd Function

See also  11 Effective Keyword Research Tools and Techniques
devxblackblue

About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

About Our Journalist