[RESOLVED] Reversed file format (Java)

[bergerkiller]

Hello everyone.

I discovered that java uses a reversed way of storing data. For example, the integer value 2 has the following byte values:

In "Windows" format:
[2] [0] [0] [0]

In "Java" format:
[0] [0] [0] [2]

The binary readers of both languages seem to use the same different format.
Now my question: What is the easiest way to read binary values (Integer, Single, etc.) in VB .NET from a java formatted file?

I already made functions like these:

    Private Shared Function revRead(ByVal s As IO.BinaryReader, ByVal length As Integer) As Byte()
        Dim rval(length - 1) As Byte
        s.Read(rval, 0, length)
        Array.Reverse(rval)
        Return rval
    End Function
    Private Shared Function readString(ByVal s As IO.BinaryReader) As String
        Dim stringlength As Short = BitConverter.ToInt16(revRead(s, 2), 0)
        Dim chars(stringlength - 1) As Char
        s.Read(chars, 0, stringlength)
        Return chars
    End Function

But they require the (slower) BitConverter to make the read bytes into a value. Is there a "vanilla way" around, some setting for inverted reading in the binary reader or a different class? Or do I have to keep using this Reverse byte method?

[ForumAccount]

This will obviously be different for different data types, but this should work for integers:

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, _
                              ByVal e As System.EventArgs) Handles Button1.Click
        Dim javaBytes = New Byte() {0, 0, 0, 2}
        Dim value = JavaConversion.ToInt32(javaBytes)

        Console.WriteLine(value)
    End Sub

End Class

Public Class JavaConversion

    '//constructors
    Private Sub New()
    End Sub

    '//methods
    Public Shared Function GetBytes(ByVal value As Integer) As Byte()
        Return New Byte() {CByte((value >> 24) And &HFF), _
                           CByte((value >> 16) And &HFF), _
                           CByte((value >> 8) And &HFF), _
                           CByte(value And &HFF)}
    End Function

    Public Shared Function ToInt32(ByVal b As Byte()) As Integer
        Return ((b(0) And &HFF) << 24) + _
               ((b(1) And &HFF) << 16) + _
               ((b(2) And &HFF) << 8) + _
               ((b(3) And &HFF))
    End Function

End Class

[bergerkiller]

Bit conversion works on integers, since it is a simple addition function (byte 0 * 2 ^ 0 + byte 1 * 2 ^ 8 etc), but I can't imagine bit conversions with Single (float) values, any way to do that?

EDIT

I see I need a function to convert a java stored integer/single into a VB .NET integer/single, like this:
(bytes) [0] [0] [0] [64]
(int) 1073741824 -> 64
(single) 2 -> 8,96831E-44

Then I could make simple overloaded functions for it:

Public Function Invert(ByVal value As Integer) As Integer
Public Function Invert(ByVal value As Single) As Single

Inverting the value twice should result in the first value.

EDIT2

Ok, I think I know what my problem is, and others have as well. I need to convert Big-Endian values to Little-Endian values and vice versa.
What I did was storing the data in a byte array and do it like that, but it requires the bitconverter to retrieve the value again.
I have seen some bit shifting that swaps the format of an integer, but what about the Single/Double/Long/Decimal (?) ?

[ForumAccount]

I think that this would be good to look through.

[Milk]

Don't mix up your bits with your bytes. Endianness is the word to research; how do you like your eggs cracked? Are you a Big-Endian or a Little-Endian?

With respect to floating point values, BitConverter is perhaps the easiest option (that I know of) in VB.Net, the documentation does discuss endianness and provides examples.

If you are familiar with C# you can use an unsafe context and pointers to do this also, perhaps quite a bit quicker than BitConverter (don't know, not tested)

[bergerkiller]

Combined the two functions of ForumAccount and ended up with this:

    Public Shared Function Endian(ByVal value As Integer) As Integer
        Return Endian(CUInt(value And &HFF))
    End Function
    Public Shared Function Endian(ByVal value As UInteger) As UInteger
        Return (value << 24) + ((value >> 8) << 16) + ((value >> 16) << 8) + (value >> 24)
    End Function

It requires quite some bit shifting, I think the bitconverter would perform better. Thanks everyone, bit converter it is, although I will make simple converters, like these:

    Public Shared Function Invert(ByVal value As Integer) As Integer
        Dim b() As Byte = BitConverter.GetBytes(value)
        Array.Reverse(b)
        Return BitConverter.ToInt32(b, 0)
    End Function
    Public Shared Function Invert(ByVal value As Single) As Single
        Dim b() As Byte = BitConverter.GetBytes(value)
        Array.Reverse(b)
        Return BitConverter.ToSingle(b, 0)
    End Function

(Please ignore the CType issues, I can always make distinct names)

MsgBox(Invert(CSng(2)))

I'll mark this thread resolved, if anyone knows of a native VB .NET method (which does not require that much bit shifting), feel free to post anyways.