sparse.c

/* 
 * sparse.c
 *
 *      This program declares a large array, but only uses a small
 *      part of it.  The intention is that the full array will not
 *      fit into memory, but the used part of the array will fit.
 *
 *      This is similar to testbin/huge.
 *
 */

#include <stdio.h>
#include <stdlib.h>

/* 
 * set these to match the page size of the 
 * machine and the number of pages of physical memory
 * in the machine.
 */
#define PageSize        4096
#define NumPages        128

/* a large array, 2 times the size of physical memory */
#define ArraySize (2*NumPages*PageSize)
char sparse[ArraySize];

int
main()
{
        int i,j;

        printf("Starting the sparse program\n");

        /* write some values into the array, but only
           touch one array entry on every 10th page */
        for (i=0; i<ArraySize; i+=(10*PageSize)) {
          sparse[i]= 'a';
        }
        
        printf("stage [1] done\n");
        
        /* increment each location 5 times */
        for(j=0; j<5; j++) {
          for (i=0; i<ArraySize; i+=(10*PageSize)) {
            sparse[i] += 1;
          }
        }
        
        printf("stage [2] done\n");
        
        /* check the values that were written */
        /* increment each location 5 times */
        for (i=0; i<ArraySize; i+=(10*PageSize)) {
          if (sparse[i] != ('a'+5)) {
            printf("Test failed! Unexpected value at array position %d\n", i);
            return(1);
          }
        }

        printf("SUCCESS\n");
        
        return 0;
}