CS360 Final -- December 10, 2002

Answers to Question 2

This is straightforward C code to do what the question asked. It is in a2.c, and below: 
/* Start time: Mon Dec  9 11:06:12 EST 2002
   Stop time:  Mon Dec  9 11:08:49 EST 2002 -- Timing -- I figure if I
   can do this in under 3 minutes, you should be able to do it in 
   under 12 minutes.  */

typedef struct flist {
  int size; 
  int checksum;
  struct flist *flink;
  struct flist *blink;
} Flist;

void free(void *p)
{
  int *x;
  Flist *f;
  
  x = (int *) p;        /* First, set f to point 8 bytes before p */
  x -= 2;
  f = (Flist *) x; 

  if (f->checksum != 1234) {    /* Check the checksum, and dump core if */
    x = NULL;                   /* is not 1234 */
    *x = 0;
  }

  f->checksum = 1235;           /* Set it to 1235 */

  f->blink = NULL;              /* Put it in the front of the freelist */
  f->flink = free_list;
  if (f->flink != NULL) f->flink->blink = f;
  free_list = f;

  return;
}

Grading: 8 points