Read or convert to Int32 from TWO byte arrays

Question

I have the 4 bytes that represent an integer stored in 2 separate byte arrays. I would like to convert these into an Int32 WITHOUT copying to a third byte array and reading that using memorystream.

The reason the data is split across two byte arrays is because this is a simplified example of my issue which involves huge amounts of data that cannot fit into a single bytearray.

Is there any way to achieve this? I do not wish to concatenate the two byte arrays into a thrid because of the performance implications which are critical to me.

Moon

Answer 1

You can use a struct layout like this

[StructLayout(LayoutKind.Explicit, Size=4)]
struct UnionInt32Value
{
[FieldOffset(0)] public byte byte1;
[FieldOffset(1)] public byte byte2;
[FieldOffset(2)] public byte byte3;
[FieldOffset(3)] public byte byte4;
[FieldOffset(0)] public Int32 iVal;
}

Assign your bytes in the correct order then read your Int32 from iVal;

EDIT: Sample code

using System;
using System.Runtime.InteropServices;
namespace Test
{
 class Program
 {
  [StructLayout(LayoutKind.Explicit, Size=4)]
  struct UnionInt32Value
  {
   [FieldOffset(0)] public byte byte1;
   [FieldOffset(1)] public byte byte2;
   [FieldOffset(2)] public byte byte3;
   [FieldOffset(3)] public byte byte4;
   [FieldOffset(0)] public Int32 iVal;
  }
  public static void Main(string[] args)
  {
   UnionInt32Value v = new UnionInt32Value();
   v.byte1=1;
   v.byte2=0;
   v.byte3=0;
   v.byte4=0;
   Console.WriteLine("this is one " + v.iVal);

   v.byte1=0xff;
   v.byte2=0xff;
   v.byte3=0xff;
   v.byte4=0xff;
   Console.WriteLine("this is minus one " + v.iVal);

   Console.Write("Press any key to continue . . . ");
   Console.ReadKey(true);
  }
 }
}

Answer 2

Something like this?

int x = (array1[index] << 16) + array2[index];

Of course, you didn't specify a language, but that's the gist of it.