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// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
package filter
import (
"encoding/binary"
"github.com/syndtr/goleveldb/leveldb/util"
"testing"
)
type harness struct {
t *testing.T
bloom Filter
generator FilterGenerator
filter []byte
}
func newHarness(t *testing.T) *harness {
bloom := NewBloomFilter(10)
return &harness{
t: t,
bloom: bloom,
generator: bloom.NewGenerator(),
}
}
func (h *harness) add(key []byte) {
h.generator.Add(key)
}
func (h *harness) addNum(key uint32) {
var b [4]byte
binary.LittleEndian.PutUint32(b[:], key)
h.add(b[:])
}
func (h *harness) build() {
b := &util.Buffer{}
h.generator.Generate(b)
h.filter = b.Bytes()
}
func (h *harness) reset() {
h.filter = nil
}
func (h *harness) filterLen() int {
return len(h.filter)
}
func (h *harness) assert(key []byte, want, silent bool) bool {
got := h.bloom.Contains(h.filter, key)
if !silent && got != want {
h.t.Errorf("assert on '%v' failed got '%v', want '%v'", key, got, want)
}
return got
}
func (h *harness) assertNum(key uint32, want, silent bool) bool {
var b [4]byte
binary.LittleEndian.PutUint32(b[:], key)
return h.assert(b[:], want, silent)
}
func TestBloomFilter_Empty(t *testing.T) {
h := newHarness(t)
h.build()
h.assert([]byte("hello"), false, false)
h.assert([]byte("world"), false, false)
}
func TestBloomFilter_Small(t *testing.T) {
h := newHarness(t)
h.add([]byte("hello"))
h.add([]byte("world"))
h.build()
h.assert([]byte("hello"), true, false)
h.assert([]byte("world"), true, false)
h.assert([]byte("x"), false, false)
h.assert([]byte("foo"), false, false)
}
func nextN(n int) int {
switch {
case n < 10:
n += 1
case n < 100:
n += 10
case n < 1000:
n += 100
default:
n += 1000
}
return n
}
func TestBloomFilter_VaryingLengths(t *testing.T) {
h := newHarness(t)
var mediocre, good int
for n := 1; n < 10000; n = nextN(n) {
h.reset()
for i := 0; i < n; i++ {
h.addNum(uint32(i))
}
h.build()
got := h.filterLen()
want := (n * 10 / 8) + 40
if got > want {
t.Errorf("filter len test failed, '%d' > '%d'", got, want)
}
for i := 0; i < n; i++ {
h.assertNum(uint32(i), true, false)
}
var rate float32
for i := 0; i < 10000; i++ {
if h.assertNum(uint32(i+1000000000), true, true) {
rate++
}
}
rate /= 10000
if rate > 0.02 {
t.Errorf("false positive rate is more than 2%%, got %v, at len %d", rate, n)
}
if rate > 0.0125 {
mediocre++
} else {
good++
}
}
t.Logf("false positive rate: %d good, %d mediocre", good, mediocre)
if mediocre > good/5 {
t.Error("mediocre false positive rate is more than expected")
}
}
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