c - Error running OPTIMAL algorithm -

****c:>pager_optimal test 100 file used fifo-test, resident set size 200

error restoring reference stream position error was:: invalid argument****/

pt_entry pte[max_page];         /* page table */ int mem_size;               /* physical memory size in page frames */ list free_list_head;            /* free list */  list res_set_head;          /* resident set */ int total_fault = 0;            /* total number of page faults */ int total_ref = 0;          /* total number of memory references */ file *stream;                   int main(int argc, char *argv[])  {    /*   file *stream;*/  if (argc != 3) {     printf("the format is: pager file_name memory_size.\n");     exit(1); }  printf("file used %s, resident set size %d\n", argv[1], atoi(argv[2]));  if ((stream = fopen(argv[1], "r")) == null) {     perror("file open failed");     exit(1); }  if( max_page >= (mem_size = atoi(argv[2])) ) {     /* fine can go ahead */     start_simulation(); } else {          printf    ("\n\n\a\a\a******************************\n");     printf("***************************************************\n");     printf("**                                               **\n");     printf("** error:                                        **\n");     printf("**                                               **\n");     printf("** attempting use resident set size **\n");     printf("** larger address space!        **\n");     printf("**                                               **\n");     printf("** maximum address space size is: %-4d       **\n",max_page);     printf("**                                               **\n");     printf("***************************************************\n");     printf("***************************************************\n\n\n");  } fclose(stream);  return 0;   }    void start_simulation(/*file * stream*/void)      {  /*char *addr_buf;not used removed --ec*/ int address; int i, n; list new_entry, current;     /* initialise page table */  for(i=0; i<max_page;i++) {     pte[i].frame = -1;     pte[i].valid = 0;     pte[i].dirty = 0;     pte[i].in_mem = 0;     pte[i].next_ref=-1;  }     /* initialise resident set - empty*/  res_set_head = (list)malloc(sizeof(struct list_item)); res_set_head->next = res_set_head; res_set_head->prev = res_set_head;    /* initialise free list - physical pages*/  free_list_head = (list)malloc(sizeof(struct list_item)); free_list_head->next = free_list_head; free_list_head->prev = free_list_head; current = free_list_head;  for(i=0; i<mem_size;i++) {     new_entry = (list)malloc(sizeof(struct list_item));     current->next = new_entry;     new_entry->prev = current;     new_entry->next = free_list_head;     new_entry->frame = i;     current = new_entry;     free_list_head->prev = current; }     /* main simulation loop */  while( (n = fscanf(stream, "%x", &address)) != -1) {    #ifdef debug2     printf("reference %i -------------\n",total_ref);    #endif      resolve(address);     total_ref++;  }  free_mem(free_list_head); free_mem(res_set_head); display_stats();  return;     }  void resolve(int address)   { unsigned short frame_alloc; int virt_page,i; /*static int disp_counter = 0;not used removed -ec*/  virt_page = address >> 8; if (pte[virt_page].valid == 1) {     pte[virt_page].next_ref=distance_to_next_ref(virt_page);    #ifdef debug2     printf("page %i valid, next reference is: %i\n",virt_page,pte             [virt_page].next_ref);    #endif } else {      frame_alloc = find_frame();     pte[virt_page].valid = 1;     pte[virt_page].frame = frame_alloc;     total_fault++;     pte[virt_page].next_ref=distance_to_next_ref(virt_page);     #ifdef debug2     printf("page %i being loaded, next reference is: %i\n",virt_page,pte     [virt_page].next_ref);    #endif } for(i=0;i<max_page;i++)     {     if (pte[i].valid) pte[i].next_ref--;     //if(pte[i].next_ref<=0) pte[i].next_ref=distance_to_next_ref(i);     /* if page valid update next ref time */     }     }    unsigned short find_frame()   { unsigned short frame; list current, new_tail;  if (free_list_head == free_list_head->prev)   /* free list empty */ {     #ifdef debug     printf("free list empty finding frame\n");     #endif      frame = find_victim(); } else {      #ifdef debug     printf("free list not empty grabbing frame\n");      #endif     new_tail = free_list_head->prev->prev;     new_tail->next = free_list_head;     current = free_list_head->prev;     free_list_head->prev = new_tail;      to_resident_set(current);     frame = current->frame; } return frame;      }   void to_resident_set(list current)    { list tail;  tail = res_set_head->prev; tail->next = current; current->next = res_set_head; current->prev = tail; res_set_head->prev = current;      }    unsigned short find_victim()     { int candidate,frame=-1,most_far=0,page;  for(candidate=0;candidate<max_page;candidate++) {      if(pte[candidate].valid==1)     {     #ifdef debug    printf("\tvalid page %i being examined, next reference is: %i\n",candidate,pte          [candidate].next_ref);    printf("pt entry:\n\t\tframe: %d\n\t\tvalid: %d\n\t\tin_mem %d\n\t\tdirty: %    d\n\t\tnext ref %d\n",pte[candidate].frame,pte[candidate].valid,pte    [candidate].in_mem,pte[candidate].dirty,pte[candidate].next_ref);    #endif         if(  (pte[candidate].next_ref) < 0 )          {    #ifdef debug    printf("\t\t< 0 page %i being examined, next reference is: %i\n",candidate,pte    [candidate].next_ref);    #endif             pte[candidate].valid=0;             frame = pte[candidate].frame;             pte[candidate].frame=-1;             return frame;         }    #ifdef debug printf("middle page %i\n",candidate);    #endif if(most_far < (pte[candidate].next_ref) )         {     #ifdef debug    printf("\t\t> mf page %i being examined, next reference is: %i\n",candidate,pte      [candidate].next_ref);     #endif    frame=pte[candidate].frame;    most_far=pte[candidate].next_ref;     }    #ifdef debug    printf("ending page %i\n",candidate);    #endif     }    } invalidate(frame); return frame;  }   void invalidate(unsigned short frame)   { int i;  for(i=0;i<max_page;i++) {     if (pte[i].frame == frame && pte[i].valid == 1)     {         pte[i].valid = 0;         pte[i].frame = -1;     #ifdef debug printf("page %i being evicted next ref is: %i\n",i,pte   [i].next_ref);     #endif         break;     }  }  }   void display_stats()     { printf("\nprocess issued %d memory references\n", total_ref); printf("process triggered %d page faults\n", total_fault); printf("page fault rate %d percent\n",((total_fault*100)/total_ref));      }   void free_mem(list head)     {  list current,tail;  tail = head->prev; current = head;  while (current->prev != tail) {     current = current->next;     free(current->prev); }    }   /* finds distance next ref, returns -1 if never referenced again */   int distance_to_next_ref(int frame)    {  long pos;  int n,count;  int address,page;    if((pos=ftell(stream))==-1) {     printf("error saving reference stream position\n");     perror("error was");     fclose(stream);     exit(1); }  count=0; while( (n = fscanf(stream, "%x", &address)) != -1) {             count++;         page=address>>8;     if(page==frame)     {         if((fseek(stream,pos,seek_set))==-1)         { printf("error restoring reference stream  position\n");             perror("error was:");             fclose(stream);         }          return count;     } } if((fseek(stream,pos,seek_set))==-1) {     printf("error restoring reference stream position\n");     perror("error was:");     fclose(stream); }  return -1;     } 

replace two printfs with

printf("error restoring reference stream position @ line %d\n", __line__); 

i suspect error not come thing comes from.