Merging 2 bytes to make an integer (Resolved)

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

VB Code:

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.

VB Code:

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

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

Do I have to do something different for long values?

VB Code:

'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? :(

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?

Its a huge negative number =(

Might be an endian issue. Try it in reverse.

VB Code:

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:

VB Code:

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.

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

:S

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

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

sod it ill parse an ascii version of the file :)

I kept getting negative numbers for file sizes on my longs

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 :-)

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.

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

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

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

VB Code:

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

and:

VB Code:

Public Type udtLong
 MyLong as Long
End Type

Fill the bytes and:

VB Code:

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

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

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

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

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:

VB Code:

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

:)

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

Lol ill just have to learn c++ :p

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

VB Code:

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 :)

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

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