int calcpay(const int rank, const float tax) __attribute__ ((pure));
int ispayday(const time_t time) __attribute__ ((pure));

int calcpay(const int rank, const float tax)
{
    switch rank {
        case 0:
            return (int) (40000.0 * (100.0 - tax));
        case 1:
            return (int) (50000.0 * (100.0 - tax));
        case 2:
            return (int) (60000.0 * (100.0 - tax));
        case 4:
            return (int) (70000.0 * (100.0 - tax));
    }
    return 0;
}

int ispayday(const time_t time)
{
    //Some deterministic function goes here
}

/*
This is the only function where we are permitted to modify e, or any other
state for that matter.
*/
void payroll(struct employee **e, const size_t esize)
{
    int i;
    time_t now;

    time(&now);

    if(ispayday(now)) {
        for(i = 0; i < esize; i++) {
            e[i]->pay = calcpay(e[i]->rank, GLOBAL_TAX);
            /*Deliver pay here - I'm guessing an API call to the financial
            provider*/
            e[i]->ispaid = 1;
        }
    }
}