Task: create basic test case and benchmark test with go

bitcount_test.go

func TestLookup(t *testing.T) {
	var tests = []struct {
		testInt uint64
		result  int
	}{
		{1213164123131294294, 30},
		{65, 2},
		{16, 1},
		{11, 3},
	}
	for _, testcase := range tests {
		if ok := LookupImprove(testcase.testInt); ok != testcase.result {
			t.Errorf("Return wrong result (%b), expect %d but got %d", testcase.testInt, testcase.result, ok)
		}
	}
}

var test uint64

func BenchmarkLookup(b *testing.B) {
	for i := 0; i < b.N; i++ {
		Lookup(test)
	}
}

func BenchmarkLookupImprove(b *testing.B) {
	for i := 0; i < b.N; i++ {
		LookupImprove(test)
	}
}

func BenchmarkAll(b *testing.B) {
	seed := time.Now().UTC().UnixNano()
	random := rand.New(rand.NewSource(seed))
	test = uint64(random.Int63())
	b.Run("lookup", BenchmarkLookup)
	b.Run("lookupImprove", BenchmarkLookupImprove)
}

bitcount.go

var table [256]byte

func init() {
	for i := range table {
		table[i] = table[i/2] + byte(i&1)
	}
}

func Lookup(v uint64) (sum int) {
	for i := 0; i < 8; i++ {
		sum += int(table[byte(v>>uint(i*8))])
	}
	return
}

func LookupImprove(v uint64) (sum int) {
	if v == 0 {
		return sum
	}
	sum = 1
	for v&(v-1) != 0 {
		v = v & (v - 1)
		sum++
	}
	return
}

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