Question

In .Net framework 2 GiB is the highest memory that you can allocate for an object. This fact is independent from platform (x64 or x86 or …).
I need to have a huge list with more than 2^30 Complex Numbers (each one is 16 bytes).

Note:

As with 32-bit Windows operating systems, there is a 2GB limit on the
size of an object you can create while running a 64-bit managed
application on a 64-bit Windows operating system.

from http://msdn.microsoft.com/en-us/library/ms241064%28VS.80%29.aspx

Answer 1

I’d implement a wrapper class that uses multiple arrays internally.

Similar to the following:

void Main()
{
    long count=3*1024*1024;
    var arr=new LargeArray<Complex>(count,12);
    for(long i=0;i<count;i++)
    {
      arr[i]=new Complex(i,-i);
    }
    for(long i=0;i<count;i++)
    {
      if(arr[i].R!=i)
        throw new Exception("Fail"+i+" "+arr[i].R);
    }
}

struct Complex
{
  public double R,I;

  public Complex(double r,double i)
    {
      R=r;
      I=i;
    }
}


class LargeArray<T>
{
  private readonly int partBits;  
  private readonly long size;

  private T[][] data;

  public T this[long index]
  {
    get
    {
      if((ulong)index>=(ulong)size)
        throw new IndexOutOfRangeException();
      int part=(int)(index>>partBits);
      int subIndex=(int)(index&((1<<partBits)-1));
      return data[part][subIndex];
    }
    set
    {
      if((ulong)index>=(ulong)size)
        throw new ArgumentOutOfRangeException();
      int part=(int)(index>>partBits);
      int subIndex=((int)index&((1<<partBits)-1));
      data[part][subIndex]=value;
    }
  }

  public LargeArray(long size,int partBits)
  {
    this.size=size;
    this.partBits=partBits;
    int partSize=1<<partBits;
    int partCount=(int)(((size-1)>>partBits)+1);
    data=new T[partCount][];
    for(int i=0;i<partCount;i++)
      data[i]=new T[partSize];
  }
}

If you use a 64 bit process this works beyond 2GB. I tried it with 5GB and apart from swapping my comp to a halt it worked.