Checksum CRC Problem

[alvinlim]

Hi, is anyone who can help me with my program? which i'm trying to calculate the checksum of the data packet 01 01 01 00 00 that is total of 5 bytes. My program is as below

[CODE=vb]Option Explicit
Dim i As Integer, j As Integer
Dim bStatus As Boolean
Dim cPacket(5) As Byte
Dim nCRC As Long

Private Sub Form_Load()
cPacket(0) = &H1
cPacket(1) = &H1
cPacket(2) = &H1
cPacket(3) = &H0
cPacket(4) = &H0
nCRC = &HFFFF

For i = 0 To Ubound(cPacket)-1
nCRC = nCRC Xor cPacket(i)
For j = 0 To 7
If ((nCRC And &H1) = True) Then
nCRC = nCRC/2
nCRC = nCRC Xor &H8408
Else
nCRC = nCRC/2
End If
Next j
Next i
Debug.Print nCRC
End Sub
[/CODE]
This program is where i was refering to the C++ code i.e.

[CODE=cpp]DWORD i,j;
for(i=0;i<nLen; i++)
{
nCRC^=cPacket[i];
for(j=0;j<8;j++ )
{
if(nCRC & 0x0001)
nCRC=(nCRC>>1) ^ 0x8408;
else
nCRC=(nCRC>>1);
}
}
return nCRC;[/CODE]

If everything is correct i should get the answer like this
data packet:01 01 01 00 00 or (0x01 0x01 0x01 0x00 0x00)
nCRC= 0x7DAB
data packet:01 00 00 00 00 or (0x01 0x00 0x00 0x00 0x00)
nCRC= 0x3BCC
But i dont know where is goes wrong....Hope anyone can help. Thanks!

[Killer42]

What is the actual problem? You just showed us the code and said what it should produce. Should we assume it isn't?

[Killer42]

At first glance, I can see one problem in the code. I'd suggest you remove the "= True" test.

When you do a boolean AND you could be producing a value anywhere between &H00 and &HFF. An IF test will take any non-zero value to indicate that it should take the "yes" branch, which is obviously what you intended. But rather than allowing VB to do this, you are explicitly comparing it to the value represented by the named constant True. If I remember correctly, this value is -1 (in hex, probably &HFF or &HFFFF).

So the first thing I would do is change
If ((nCRC And &H1) = True) Then
to
If (nCRC And &H1) Then

You could also get away with this, if you really wanted to...
If ((nCRC And &H1) <> False) Then