Merging 2 bytes to make an integer (Resolved)

[BodwadUK]

Hello,

If I load all file details into a binary array how would I convert two of those binary entries into an integer or long?

e.g

Dim FileBinary() as byte
    Dim intFile as integer
    Dim intTest as integer
 
    'Read in the whole file to a binary array
    intFile = FreeFile
    ReDim FileBinary(Len(Filename))
    Open Filename For Binary Access Read As intFile Len = 1
        Get intFile, 1, FileBinary
    Close intFile
 
    'How do I now read the first two elements as though they were an integer
    intTest = FileBinary(0) & Filebinary(1) 'doesnt work

I hope this makes sense. The application I am writting reads in a third part file and needs to be read in as bytes so that I can process the file correctly. i cant therefore load in the value straight to an integer as I dont actually know its an integer until I have the file information.

[penagate]

Declare Sub RtlMoveMemory Lib "kernel32" ( _
  ByRef lpvDest As Any, _
  ByRef lpvSrc As Any, _
  ByVal cbLen As Long _
)
 
' --
 
RtlMoveMemory ByVal VarPtr(intTest), FileBinary(0), 1
RtlMoveMemory ByVal VarPtr(intTest) + 1, FileBinary(1), 1

[BodwadUK]

Brilliant that even helps with converting to other vars too. Have a rep point

[BodwadUK]

Do I have to do something different for long values?

'Calculate The Long
    RtlMoveMemory ByVal VarPtr(ReturnLong), Binary(Startpos), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 1, Binary(Startpos + 1), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 2, Binary(Startpos + 2), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 3, Binary(Startpos + 3), 1

Doesnt seem to work for this?

[penagate]

Hmm. It should, unless my memory is playing tricks with me.

What do you get? Is it hideously big or negative in comparison to what you should be getting?

[BodwadUK]

Its a huge negative number =(

[penagate]

Might be an endian issue. Try it in reverse.

RtlMoveMemory ByVal VarPtr(ReturnLong), Binary(Startpos + 3), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 1, Binary(Startpos + 2), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 2, Binary(Startpos + 1), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 3, Binary(Startpos), 1

Or failing that:

RtlMoveMemory ByVal VarPtr(ReturnLong), Binary(Startpos + 2), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 1, Binary(Startpos + 3), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 2, Binary(Startpos), 1
    RtlMoveMemory ByVal VarPtr(ReturnLong) + 3, Binary(Startpos + 1), 1

See if either of those work.

[BodwadUK]

No they didnt work either. I must be doing something really stupid in my program because logically it should work

[penagate]

:S

What exactly do you get, and what exactly should you get? I'll see if I can spot what's wrong.

[leinad31]

intTest = (FileBinary(0) * (2^8)) OR Filebinary(1)

[BodwadUK]

sod it ill parse an ascii version of the file

I kept getting negative numbers for file sizes on my longs

[smUX]

Filesizes? Are you getting the filesizes for files on your local drive? There's simple enough methods for doing that using only a few lines of code...basically open the file for reading, do a siz=LOF(1) and close it (assuming you opened it using #1...change that if not)...LOF is "Length Of File" and would return the exact byte size to the variable siz :-)

[BodwadUK]

No sorry the file contains zip files. I am trying to decode the .cob format of truespace which contains a zip file embedded within it.

[smUX]

Ah, I see (walks away more confused than before) :-P

[leinad31]

If the result is negative then the highest order bit was set to 1... will removing this bit give you the correct size?

intTest = intTest AND 65535

lngTest = lngTest AND 4294967295

[namrekka]

What I always do, however MS doesn't recommend, is making 2 UDT:

Public Type udtLongByte
 Byte1 as Byte
 Byte2 as Byte
 Byte3 as Byte
 Byte4 as Byte
End Type

and:

Public Type udtLong
 MyLong as Long
End Type

Fill the bytes and:

Dim LongByte as udtLongByte
 Dim LongValue as udtLong
 
 LongByte.Byte1=..
 LongByte.Byte2=..
 LongByte.Byte3=..
 LongByte.Byte4=..
 
 LSet LongValue=LongByte
 
 ...=LongValue.MyLong

[BodwadUK]

I have tried both but they didnt work and had the same result.

Does anyone know which "bit" is the negative trigger? I always thought it was the first one.

I am trying to do a bit operation on it to see if that does it


EDIT:::: How random if I go back and grab the data by opening the file and getting the long at that exact location, then the value is different (and correct). How wierd

[BodwadUK]

oh ffs its got to be a badly written file. It isnt different if I grab it from the file

[namrekka]

Could the problem be that VB has no unsigned variables? Are you sure that the expected values are in range?

[Merri]

Long is limited to 2147483647 (&H7FFFFFFF) in positive numbers. So, about the only thing we can do is to use something else to handle the numbers properly. Thus this leads us to one solution: use Currency. Unfortunatenaly we can't use bitwise operators for Currency, which forces us to use even more basic math. So to finally get what you want:

Option Explicit
 
Private Sub Form_Load()
    Dim Bytes(3) As Byte, curTest As Currency
    Bytes(0) = &HFF
    Bytes(1) = &HFF
    Bytes(2) = &HFF
    Bytes(3) = &HFF
    curTest = Bytes(0) * CCur(&H1000000) + Bytes(1) * CCur(&H10000) + _
        Bytes(2) * CCur(&H100&) + Bytes(3)
    MsgBox curTest
End Sub

[BodwadUK]

The specification document doesnt say its unsigned and the zip certainly isnt very big. Ho hum

Lol ill just have to learn c++

[Merri]

Also, if you want to read Long directly from file and convert it to Currency without hassling with bytes and API like that:

Private Sub Form_Load()
    Dim lngTest As Long, curTest As Currency
    lngTest = CLng(-1)
    If lngTest < 0 Then
        curTest = CCur(lngTest And &H7FFFFFFF) + 2147483648#
    Else
        curTest = lngTest
    End If
    MsgBox curTest
End Sub

Believe me, this is also faster than doing four calls of RtlMoveMemory

[namrekka]

Signed values are according 2’s complement.
If you have a 3 bits variable then:

Signed Unsigned
000 0 0
001 1 1
010 2 2
011 3 3
111 7 -1
110 6 -2
101 5 -3
100 4 -4

So flipping the sign bit will not solve your problem. In this case you can do (pseudo code):
If var <0 then vardef = 8 - var
If var =>0 then vardef = var

[BodwadUK]

thanks everyone but I have given up for now. I will just have to text parse an ascii file when I can be bothered