How to pass an array of bytes as a Pointer in C#

Question

Hello,

I have two questions.They both are concerning a void in C++,which I am trying to translate in C#.

C++ code

void Func_X_2(LPBYTE stream, DWORD key, BYTE keyByte)
{
stream[0] ^= (stream[0] + LOBYTE(LOWORD(key)) + keyByte);
stream[1] ^= (stream[1] + HIBYTE(LOWORD(key)) + keyByte);
stream[2] ^= (stream[2] + LOBYTE(HIWORD(key)) + keyByte);
stream[3] ^= (stream[3] + HIBYTE(HIWORD(key)) + keyByte);
stream[4] ^= (stream[4] + LOBYTE(LOWORD(key)) + keyByte);
stream[5] ^= (stream[5] + HIBYTE(LOWORD(key)) + keyByte);
stream[6] ^= (stream[6] + LOBYTE(HIWORD(key)) + keyByte);
stream[7] ^= (stream[7] + HIBYTE(HIWORD(key)) + keyByte);
}

First question:

DWORD is UInt32,BYTE is byte,but what is LPBYTE? How to use it as an array?

Second question:

How to use LOBYTE,HIBYTE,LOWORD,HIWORD in C#?

EDIT

This is how the function is being called: C++ code

Func_X_2((LPBYTE)keyArray, dwArgs[14], keyByte);

keyArray is a DWORD(UInt32),dwArgs is an array of dword.KeyByte is a byte.

Thanks in advance.

Answer 1

LPBYTE stands for Long Pointer to Byte, so it's effectively a Byte array.

If you have an uint32, u (have to be careful shifting signed quantities):

LOWORD(u) =  (u & 0xFFFF);
HIWORD(u) =  (u >> 16);

assumes only bottom 16 bits set (ie. top 16 bits zero):

LOBYTE(b) = (b & 0xFF);
HIBYTE(b) = (b >> 8);

Answer 2

[...] what is LPBYTE? How to use it as an array?

It is a pointer to BYTE: a typedef, usually for unsigned char. You use it as you would use an unsigned char* to point to the first element of an array of unsigned characters. It is defined in windef.h:

typedef unsigned char       BYTE;    
typedef BYTE far            *LPBYTE;

How to use LOBYTE,HIBYTE,LOWORD,HIWORD in C#?

These are macros to fetch parts of a WORD. They are very easy to implement (as bit-fiddling operatios). These are also defined in windef.h. You can simply take the definitions out and paste it into custom C# functions:

#define LOWORD(l)           ((WORD)((DWORD_PTR)(l) & 0xffff))
#define HIWORD(l)           ((WORD)((DWORD_PTR)(l) >> 16))
#define LOBYTE(w)           ((BYTE)((DWORD_PTR)(w) & 0xff))
#define HIBYTE(w)           ((BYTE)((DWORD_PTR)(w) >> 8))

You may want to look at this SO post also for bit manipulation in C#.

Answer 3

LPBYTE is a pointer to a byte array. The equivalent in C# would be a variable of type byte[]. So you could translate your function like so:

public static void Func_X_2(byte[] stream, int key, byte keyByte)
{
    stream[0] ^= (byte)(stream[0] + BitConverter.GetBytes(LoWord(key))[0]);
    stream[1] ^= (byte)(stream[1] + BitConverter.GetBytes(LoWord(key))[1]);
    stream[2] ^= (byte)(stream[2] + BitConverter.GetBytes(HiWord(key))[0]);
    stream[3] ^= (byte)(stream[3] + BitConverter.GetBytes(HiWord(key))[1]);
    stream[4] ^= (byte)(stream[4] + BitConverter.GetBytes(LoWord(key))[0]);
    stream[5] ^= (byte)(stream[5] + BitConverter.GetBytes(LoWord(key))[1]);
    stream[6] ^= (byte)(stream[6] + BitConverter.GetBytes(HiWord(key))[0]);
    stream[7] ^= (byte)(stream[7] + BitConverter.GetBytes(HiWord(key))[1]);
}

public static int LoWord(int dwValue)
{
    return (dwValue & 0xFFFF);
}

public static int HiWord(int dwValue)
{
    return (dwValue >> 16) & 0xFFFF;
}