[Yaffs] mkyaffs2image object file size is wrong???

when compiling  mkyaffs2image tool , I  add some debug message in function write_object_header:

static int write_object_header(int id, enum yaffs_obj_type t, struct stat *s, int parent, const char *name, int equivalentObj, const char * alias)
{

     ......
    if(t == YAFFS_OBJECT_TYPE_FILE)
    {
        oh->file_size_low = s->st_size;
        oh->file_size_high = (s->st_size >> 32);

        printf("name=%s s->st_size:%lu file_size_low:%u file_size_hight=%u\n", 
            oh->name, s->st_size, oh->file_size_low,oh->file_size_high);
        
    }
      ......
}

then I got the debug info like this:
Object 416, rootfs/bin/busybox is a file, name=busybox s->st_size:830472 file_size_low:830472 file_size_hight=830472

my question is   why file_size_low is equal to file_size_hight ??   I  use 32 bit linux systerm. 



BestRegards