Question

For my university process I’m simulating a process called random sequential adsorption.
One of the things I have to do involves randomly depositing squares (which cannot overlap) onto a lattice until there is no more room left, repeating the process several times in order to find the average ‘jamming’ coverage %.

Basically I’m performing operations on a large array of integers, of which 3 possible values exist: 0, 1 and 2. The sites marked with ‘0’ are empty, the sites marked with ‘1’ are full. Initially the array is defined like this:

int i, j;
int n = 1000000000;
int array[n][n];

for(j = 0; j < n; j++)
{
    for(i = 0; i < n; i++)
    {
        array[i][j] = 0;
    }
}

Say I want to deposit 5*5 squares randomly on the array (that cannot overlap), so that the squares are represented by ‘1’s. This would be done by choosing the x and y coordinates randomly and then creating a 5*5 square of ‘1’s with the topleft point of the square starting at that point. I would then mark sites near the square as ‘2’s. These represent the sites that are unavailable since depositing a square at those sites would cause it to overlap an existing square. This process would continue until there is no more room left to deposit squares on the array (basically, no more ‘0’s left on the array)

Anyway, to the point. I would like to make this process as efficient as possible, by using bitwise operations. This would be easy if I didn’t have to mark sites near the squares. I was wondering whether creating a 2-bit number would be possible, so that I can account for the sites marked with ‘2’.

Sorry if this sounds really complicated, I just wanted to explain why I want to do this.

Answer 1

Instead of a two-bit array you could use two separate 1-bit arrays. One holds filled squares and one holds adjacent squares (or available squares if this is more efficient).

I’m not really sure that this has any benefit though over packing 2-bit fields into words.
I’d go for byte arrays unless you are really short of memory.