Remove intersection

Author: korthaj

example_test.go

@@ -51,29 +51,25 @@ func Example_falsePositives() {
 	// Output: 26 mistakes were made.
 }
 
-// Compute the intersection and union of two filters.
-func ExampleFilter_And() {
+// Compute the union of two filters.
+func ExampleFilter_Or() {
 	// Create two Bloom filter with room for 1000 elements
 	// at a false-positives rate less than 1/100.
-	n := 1000
-	p := 100
-	f1, f2 := bloom.New(n, p), bloom.New(n, p)
+	n, p := 1000, 100
+	f1 := bloom.New(n, p)
+	f2 := bloom.New(n, p)
 
-	// Add "0", "1", …, "499" to f1
-	for i := 0; i < n/2; i++ {
+	// Add "0", "2", …, "498" to f1
+	for i := 0; i < n/2; i += 2 {
 		f1.Add(strconv.Itoa(i))
 	}
 
-	// Add "250", "251", …, "749" to f2
-	for i := n / 4; i < 3*n/4; i++ {
+	// Add "1", "3", …, "499" to f2
+	for i := 1; i < n/2; i += 2 {
 		f2.Add(strconv.Itoa(i))
 	}
 
-	// Compute the approximate size of f1 ∩ f2 and f1 ∪ f2.
-	fmt.Println("f1 ∩ f2:", f1.And(f2).Count())
+	// Compute the approximate size of f1 ∪ f2.
 	fmt.Println("f1 ∪ f2:", f1.Or(f2).Count())
-	// Output:
-	// f1 ∩ f2: 276
-	// f1 ∪ f2: 758
-
+	// Output: f1 ∪ f2: 505
 }

filter.go

@@ -122,43 +122,12 @@ func (f *Filter) Count() int64 {
 	return f.count
 }
 
-// And returns a new Bloom filter that consists of all elements
-// that belong to both f1 and f2. The two filters must be of
-// the same size and have the same false-positives rate.
-//
-// The false-positive rate of the resulting filter is bounded by
-// the maximum false-positive rate of f1 and f2, but it may be larger
-// than the rate of the filter created from scratch using
-// the intersection of the two sets.
-func (f1 *Filter) And(f2 *Filter) *Filter {
-	if len(f1.data) != len(f2.data) || f1.lookups != f2.lookups {
-		panic("operation requires filters of the same type")
-	}
-	len := len(f1.data)
-	res := &Filter{
-		data:    make([]uint64, len),
-		lookups: f1.lookups,
-	}
-	bitCount := 0
-	for i := 0; i < len; i++ {
-		w := f1.data[i] & f2.data[i]
-		res.data[i] = w
-		bitCount += count(w)
-	}
-	// Estimate the number of elements from the bitCount.
-	m := 64 * float64(len)
-	bits := float64(bitCount)
-	n := m / float64(f1.lookups) * math.Log(m/(m-bits))
-	res.count = int64(n)
-	return res
-}
-
 // Or returns a new Bloom filter that consists of all elements
 // that belong to either f1 or f2. The two filters must be of
-// the same size and have the same false-positives rate.
+// the same size n and have the same false-positives rate p.
 //
-// The resulting filter is the same as the filter created from scratch
-// using the union of the two sets.
+// The resulting filter is the same as the filter created
+// from scratch using the union of the two sets.
 func (f1 *Filter) Or(f2 *Filter) *Filter {
 	if len(f1.data) != len(f2.data) || f1.lookups != f2.lookups {
 		panic("operation requires filters of the same type")

filter_test.go

@@ -58,7 +58,7 @@ func TestFilter(t *testing.T) {
 	}
 }
 
-func TestAndOr(t *testing.T) {
+func TestOr(t *testing.T) {
 	s1 := "asöldkgjaösldkgaösldkasldgjkaösldkgjöasgkdjg"
 	s2 := "elasödlnkgaölsdkfgaölsdkjfaölsdkgaölskgnaösl"
 	s3 := "aölsdgkaösldkgaösldkgjaölsdkjgaölsdkgjaösldk"
@@ -69,20 +69,8 @@ func TestAndOr(t *testing.T) {
 			f1.Add(s2)
 			f2.Add(s2)
 			f2.Add(s3)
-			and, or := f1.And(f2), f1.Or(f2)
-			member := and.Test(s1)
-			if member {
-				t.Errorf("and.Test(s1) = %v; want false\n", member)
-			}
-			member = and.Test(s2)
-			if !member {
-				t.Errorf("and.Test(s2) = %v; want true\n", member)
-			}
-			member = and.Test(s3)
-			if member {
-				t.Errorf("and.Test(s3) = %v; want false\n", member)
-			}
-			member = or.Test(s1)
+			or := f1.Or(f2)
+			member := or.Test(s1)
 			if !member {
 				t.Errorf("or.Test(s1) = %v; want true\n", member)
 			}
@@ -138,13 +126,13 @@ func BenchmarkTestByte(b *testing.B) {
 	}
 }
 
-func BenchmarkTestAnd(b *testing.B) {
+func BenchmarkTestOr(b *testing.B) {
 	n := 1000
 	b.StopTimer()
 	f1 := New(n, 200)
 	f2 := New(n, 200)
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
-		_ = f1.And(f2)
+		_ = f1.Or(f2)
 	}
 }