typedef struct nd_t { struct nd_t *next; 
                      /*and other components*/  } node_t;

#define BLOCKSIZE 256

node_t *currentblock = NULL;
int    size_left;
node_t *free_list = NULL;

node_t *get_node()
{ node_t *tmp;
  if( free_list != NULL )
  {  tmp = free_list;
     free_list = free_list -> next;
  }
  else
  {  if( currentblock == NULL || size_left == 0)
     {  currentblock = 
                (node_t *) malloc( BLOCKSIZE * sizeof(node_t) );
        size_left = BLOCKSIZE;
     }
     tmp = currentblock++;
     size_left -= 1;
  }
  return( tmp );
}


void return_node(node_t *node)
{  node->next = free_list;
   free_list = node;
}