func TestPi(t *testing.T) {
cases := []struct {
n int
want int
}{
{10, 4},
{100, 25},
{1000, 168},
{10000, 1229},
{100000, 9592},
{1000000, 78498},
{10000000, 664579},
{100000000, 5761455},
{1000000000, 50847534},
{104730, 10000},
}
// Maximum relative error when Pi(n) returns an estimate
const epsMax = 0.01
for _, c := range cases {
pi, ok := primes.Pi(c.n)
if ok {
if pi != c.want {
t.Errorf("Pi(%d) == (%d,true), want %d", c.n, pi, c.want)
}
} else {
eps := math.Abs(float64(pi-c.want) / float64(c.want))
if eps >= epsMax {
t.Errorf("Pi(%d) == (%d,false), want %d; eps=%f", c.n, pi, c.want, eps)
}
}
}
}
func ExamplePi() {
// Check how many prime numbers are less than or equal to n
ns := []int{6, 11, 23, 12345}
for _, n := range ns {
pi, ok := primes.Pi(n)
if ok {
fmt.Printf("There are %d primes in [0,%d]\n", pi, n)
} else {
fmt.Printf("There are approximately %d primes in [0,%d]\n", pi, n)
}
}
// Output:
// There are 3 primes in [0,6]
// There are 5 primes in [0,11]
// There are 9 primes in [0,23]
// There are approximately 1465 primes in [0,12345]
}