RNG seeding using crypto/rand uint64

fastrand.go

@@ -6,25 +6,29 @@
 package fastrand
 
 import (
+	"crypto/rand"
+	"encoding/binary"
 	"sync"
-	"time"
 )
 
 // Uint32 returns pseudorandom uint32.
 //
 // It is safe calling this function from concurrent goroutines.
 func Uint32() uint32 {
 	v := rngPool.Get()
-	if v == nil {
-		v = &RNG{}
-	}
 	r := v.(*RNG)
 	x := r.Uint32()
 	rngPool.Put(r)
 	return x
 }
 
-var rngPool sync.Pool
+var rngPool = sync.Pool{
+	New: func() interface{} {
+		return &RNG{
+			x: getRandomUint32(),
+		}
+	},
+}
 
 // Uint32n returns pseudorandom uint32 in the range [0..maxN).
 //
@@ -46,10 +50,6 @@ type RNG struct {
 //
 // It is unsafe to call this method from concurrent goroutines.
 func (r *RNG) Uint32() uint32 {
-	for r.x == 0 {
-		r.x = getRandomUint32()
-	}
-
 	// See https://en.wikipedia.org/wiki/Xorshift
 	x := r.x
 	x ^= x << 13
@@ -69,6 +69,8 @@ func (r *RNG) Uint32n(maxN uint32) uint32 {
 }
 
 func getRandomUint32() uint32 {
-	x := time.Now().UnixNano()
+	b := make([]byte, 8)
+	_, _ = rand.Read(b)
+	x := binary.BigEndian.Uint64(b)
 	return uint32((x >> 32) ^ x)
 }

fastrand_test.go

@@ -5,18 +5,29 @@ import (
 )
 
 func TestUint32(t *testing.T) {
-	m := make(map[uint32]struct{})
+	m := make(map[uint32]int)
 	for i := 0; i < 1e6; i++ {
 		n := Uint32()
-		if _, ok := m[n]; ok {
-			t.Fatalf("number %v already exists", n)
+		m[n]++
+	}
+
+	const minUniqueValues = 0.9 * 1e6
+	if len(m) < minUniqueValues {
+		t.Errorf("only %d unique numbers were generated", len(m))
+	}
+
+	const maxRepetition = 3
+	for number, count := range m {
+		if count > maxRepetition {
+			t.Errorf("number %d was generated %d times", number, count)
 		}
-		m[n] = struct{}{}
 	}
 }
 
 func TestRNGUint32(t *testing.T) {
-	var r RNG
+	r := RNG{
+		x: getRandomUint32(),
+	}
 	m := make(map[uint32]struct{})
 	for i := 0; i < 1e6; i++ {
 		n := r.Uint32()
@@ -51,7 +62,9 @@ func TestUint32n(t *testing.T) {
 }
 
 func TestRNGUint32n(t *testing.T) {
-	var r RNG
+	r := RNG{
+		x: getRandomUint32(),
+	}
 	m := make(map[uint32]int)
 	for i := 0; i < 1e6; i++ {
 		n := r.Uint32n(1e2)

fastrand_timing_test.go

@@ -128,3 +128,9 @@ func BenchmarkMathRandRNGInt31nArray(b *testing.B) {
 		atomic.AddUint32(&BenchSink, s)
 	})
 }
+
+func Benchmark_getRandomUint32(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		getRandomUint32()
+	}
+}

go.mod

@@ -1 +1,3 @@
 module github.com/valyala/fastrand
+
+go 1.16