Memory for Nios II Software

I am using a 12K on chip memory for my Nios II system. In my software code, I am using an Integer array of length 500000. But I am wondering how it can be implemented on a 12k on chip memory?!!!. the project is built succesfully with no shortage of memory. Here is my code:

# include "system.h"

int main(void)

{

volatile unsigned int * read_ptr = (unsigned int *) (READ_PORT_BASE + 1);

volatile unsigned int * write_ptr = (unsigned int *) (WRITE_PORT_BASE + 1);

unsigned int temp;

int length = 500000;

unsigned int buff[length];

while(1)

{

buff[0] = (* read_ptr);

for (int i = 1; i < length - 1; i++)

{

temp = buff;

buff = buff[i - 1];

buff[i + 1] = temp;

}

temp = buff[0] + buff[length];

(* write_ptr) = temp;

}

}