initial import

core/mathx/entropy.go

@@ -0,0 +1,14 @@
+package mathx
+
+import "math"
+
+func CalcEntropy(m map[interface{}]int, total int) float64 {
+	var entropy float64
+
+	for _, v := range m {
+		proba := float64(v) / float64(total)
+		entropy -= proba * math.Log2(proba)
+	}
+
+	return entropy / math.Log2(float64(len(m)))
+}

core/mathx/entropy_test.go

@@ -0,0 +1,17 @@
+package mathx
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestCalcEntropy(t *testing.T) {
+	const total = 1000
+	const count = 100
+	m := make(map[interface{}]int, total)
+	for i := 0; i < total; i++ {
+		m[i] = count
+	}
+	assert.True(t, CalcEntropy(m, total*count) > .99)
+}

core/mathx/int.go

@@ -0,0 +1,17 @@
+package mathx
+
+func MaxInt(a, b int) int {
+	if a > b {
+		return a
+	} else {
+		return b
+	}
+}
+
+func MinInt(a, b int) int {
+	if a < b {
+		return a
+	} else {
+		return b
+	}
+}

core/mathx/int_test.go

@@ -0,0 +1,71 @@
+package mathx
+
+import (
+	"testing"
+
+	"zero/core/stringx"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMaxInt(t *testing.T) {
+	cases := []struct {
+		a      int
+		b      int
+		expect int
+	}{
+		{
+			a:      0,
+			b:      1,
+			expect: 1,
+		},
+		{
+			a:      0,
+			b:      -1,
+			expect: 0,
+		},
+		{
+			a:      1,
+			b:      1,
+			expect: 1,
+		},
+	}
+
+	for _, each := range cases {
+		t.Run(stringx.Rand(), func(t *testing.T) {
+			actual := MaxInt(each.a, each.b)
+			assert.Equal(t, each.expect, actual)
+		})
+	}
+}
+
+func TestMinInt(t *testing.T) {
+	cases := []struct {
+		a      int
+		b      int
+		expect int
+	}{
+		{
+			a:      0,
+			b:      1,
+			expect: 0,
+		},
+		{
+			a:      0,
+			b:      -1,
+			expect: -1,
+		},
+		{
+			a:      1,
+			b:      1,
+			expect: 1,
+		},
+	}
+
+	for _, each := range cases {
+		t.Run(stringx.Rand(), func(t *testing.T) {
+			actual := MinInt(each.a, each.b)
+			assert.Equal(t, each.expect, actual)
+		})
+	}
+}

core/mathx/proba.go

@@ -0,0 +1,26 @@
+package mathx
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+)
+
+type Proba struct {
+	// rand.New(...) returns a non thread safe object
+	r    *rand.Rand
+	lock sync.Mutex
+}
+
+func NewProba() *Proba {
+	return &Proba{
+		r: rand.New(rand.NewSource(time.Now().UnixNano())),
+	}
+}
+
+func (p *Proba) TrueOnProba(proba float64) (truth bool) {
+	p.lock.Lock()
+	truth = p.r.Float64() < proba
+	p.lock.Unlock()
+	return
+}

core/mathx/proba_test.go

@@ -0,0 +1,24 @@
+package mathx
+
+import (
+	"math"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTrueOnProba(t *testing.T) {
+	const proba = math.Pi / 10
+	const total = 100000
+	const epsilon = 0.05
+	var count int
+	p := NewProba()
+	for i := 0; i < total; i++ {
+		if p.TrueOnProba(proba) {
+			count++
+		}
+	}
+
+	ratio := float64(count) / float64(total)
+	assert.InEpsilon(t, proba, ratio, epsilon)
+}

core/mathx/unstable.go

@@ -0,0 +1,41 @@
+package mathx
+
+import (
+	"math/rand"
+	"sync"
+	"time"
+)
+
+type Unstable struct {
+	deviation float64
+	r         *rand.Rand
+	lock      *sync.Mutex
+}
+
+func NewUnstable(deviation float64) Unstable {
+	if deviation < 0 {
+		deviation = 0
+	}
+	if deviation > 1 {
+		deviation = 1
+	}
+	return Unstable{
+		deviation: deviation,
+		r:         rand.New(rand.NewSource(time.Now().UnixNano())),
+		lock:      new(sync.Mutex),
+	}
+}
+
+func (u Unstable) AroundDuration(base time.Duration) time.Duration {
+	u.lock.Lock()
+	val := time.Duration((1 + u.deviation - 2*u.deviation*u.r.Float64()) * float64(base))
+	u.lock.Unlock()
+	return val
+}
+
+func (u Unstable) AroundInt(base int64) int64 {
+	u.lock.Lock()
+	val := int64((1 + u.deviation - 2*u.deviation*u.r.Float64()) * float64(base))
+	u.lock.Unlock()
+	return val
+}

core/mathx/unstable_test.go

@@ -0,0 +1,71 @@
+package mathx
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUnstable_AroundDuration(t *testing.T) {
+	unstable := NewUnstable(0.05)
+	for i := 0; i < 1000; i++ {
+		val := unstable.AroundDuration(time.Second)
+		assert.True(t, float64(time.Second)*0.95 <= float64(val))
+		assert.True(t, float64(val) <= float64(time.Second)*1.05)
+	}
+}
+
+func TestUnstable_AroundInt(t *testing.T) {
+	const target = 10000
+	unstable := NewUnstable(0.05)
+	for i := 0; i < 1000; i++ {
+		val := unstable.AroundInt(target)
+		assert.True(t, float64(target)*0.95 <= float64(val))
+		assert.True(t, float64(val) <= float64(target)*1.05)
+	}
+}
+
+func TestUnstable_AroundIntLarge(t *testing.T) {
+	const target int64 = 10000
+	unstable := NewUnstable(5)
+	for i := 0; i < 1000; i++ {
+		val := unstable.AroundInt(target)
+		assert.True(t, 0 <= val)
+		assert.True(t, val <= 2*target)
+	}
+}
+
+func TestUnstable_AroundIntNegative(t *testing.T) {
+	const target int64 = 10000
+	unstable := NewUnstable(-0.05)
+	for i := 0; i < 1000; i++ {
+		val := unstable.AroundInt(target)
+		assert.Equal(t, target, val)
+	}
+}
+
+func TestUnstable_Distribution(t *testing.T) {
+	const (
+		seconds = 10000
+		total   = 10000
+	)
+
+	m := make(map[int]int)
+	expiry := NewUnstable(0.05)
+	for i := 0; i < total; i++ {
+		val := int(expiry.AroundInt(seconds))
+		m[val]++
+	}
+
+	_, ok := m[0]
+	assert.False(t, ok)
+
+	mi := make(map[interface{}]int, len(m))
+	for k, v := range m {
+		mi[k] = v
+	}
+	entropy := CalcEntropy(mi, total)
+	assert.True(t, len(m) > 1)
+	assert.True(t, entropy > 0.95)
+}