the use of static, get wrong result

Who can tell me why I get the wrong result？

function：

alt_u64 tpm_get_ticks(void)

{

static alt_u64 old_t=0 ;

alt_u64 new_t=0;

alt_u64 res_t=0;

new_t = alt_timestamp();

printf("\n 1 new_t=%x, old_t=%x \n",new_t,old_t);

old_t = new_t;

printf("\n 2 new_t=%x, old_t=%x \n",new_t,old_t);

res_t = (old_t > 0) ? new_t - old_t : 0;

printf("\n 3 new_t=%x, old_t=%x \n",new_t,old_t);

return res_t;

}

result：

1 new_t=f5f86c4e, old_t=a

2 new_t=f5f86c4e, old_t=a

3 new_t=f5f86c4e, old_t=a