func TestSieve(t *testing.T) {
cases := []struct {
n int // input to Sieve(n)
want int // expected largest prime <= n (0 if it does not exist)
}{
{-1, 0},
{0, 0},
{1, 0},
{2, 2},
{3, 3},
{4, 3},
{1229, 1229},
{100, 97},
{1000, 997},
{10000, 9973},
{100000, 99991},
{200000, 199999},
{500000, 499979},
{1000000, 999983},
}
for _, c := range cases {
ps := primes.Sieve(c.n)
if c.want > 0 {
if len(ps) == 0 {
t.Errorf("Sieve(%d) == [], want something", c.n)
} else if last := ps[len(ps)-1]; last != c.want {
t.Errorf("Sieve(%d)[-1] == %d, want %d", c.n, last, c.want)
}
} else {
if l := len(ps); l > 0 {
t.Errorf("|Sieve(%d)| == %d, want 0", c.n, l)
}
}
}
}
func ExampleSieve() {
// Generate the prime numbers less than or equal to 20
ps := primes.Sieve(20)
fmt.Println(ps)
// Output: [2 3 5 7 11 13 17 19]
}
func TestSieveAgainstBaseline(t *testing.T) {
ns := []int{0, 1, 2, 3, 10000000}
for _, n := range ns {
ps := primes.Sieve(n)
qs := baselineSieve(n)
if len(ps) != len(qs) {
t.Errorf("SieveAgainstBaseline(%d): len == %d, want %d", n, len(ps), len(qs))
break
}
for i, p := range ps {
if p != qs[i] {
t.Errorf("SieveAgainstBaseline(%d): [%d] == %d, want %d", n, i, p, qs[i])
break
}
}
}
}