Perf: avoid using rand.Rand casting

entropy/entropy.go

@@ -4,8 +4,11 @@ import (
 	crip "crypto/rand"
 	"encoding/binary"
 	"math/rand"
+	"os"
+	"reflect"
 	"sync"
 	"time"
+	"unsafe"
 
 	"nullprogram.com/x/rng"
 
@@ -16,11 +19,11 @@ type randPool struct {
 	sync.Pool
 }
 
-func (p *randPool) Get() *rand.Rand {
-	return p.Pool.Get().(*rand.Rand)
+func (p *randPool) Get() *rng.SplitMix64 {
+	return p.Pool.Get().(*rng.SplitMix64)
 }
 
-func (p *randPool) Put(r *rand.Rand) {
+func (p *randPool) Put(r *rng.SplitMix64) {
 	p.Pool.Put(r)
 }
 
@@ -30,8 +33,7 @@ var (
 			New: func() interface{} {
 				sm64 := new(rng.SplitMix64)
 				sm64.Seed(GetCryptoSeed())
-				prng := rand.New(sm64) //nolint:gosec
-				return prng
+				return sm64
 			},
 		},
 	}
@@ -42,16 +44,18 @@ var (
 
 func setSharedRand() {
 	hardLocc.Lock()
-	sharedRand = lolXD.Get()
+	sharedRand = rand.New(lolXD.Get())
 	hardLocc.Unlock()
 }
 
 func AcquireRand() *rand.Rand {
-	return lolXD.Get()
+	return rand.New(lolXD.Get())
 }
 
 func ReleaseRand(r *rand.Rand) {
-	lolXD.Put(r)
+	srcField := reflect.ValueOf(r).Elem().FieldByName("src")
+	src := reflect.NewAt(srcField.Type(), unsafe.Pointer(srcField.UnsafeAddr())).Elem().Interface().(*rng.SplitMix64)
+	lolXD.Put(src)
 	r = nil
 }
 
@@ -80,18 +84,17 @@ func GetOptimizedRand() *rand.Rand {
 }
 
 // GetSharedRand returns a pointer to our shared optimized rand.Rand which uses crypto/rand to seed a splitmix64 rng.
-// WARNING - RACY - This is not thread safe, and should only be used in a single-threaded context.
 func GetSharedRand() *rand.Rand {
 	getSharedRand.Do(func() {
 		setSharedRand()
 	})
-	return sharedRand
+	return rand.New(sharedRand)
 }
 
 // RNGUint32 returns a random uint32 using crypto/rand and splitmix64.
 func RNGUint32() uint32 {
 	r := lolXD.Get()
-	ui := r.Uint32()
+	ui := uint32(r.Int63() >> 31)
 	lolXD.Put(r)
 	return ui
 }
@@ -106,8 +109,25 @@ RNG returns integer with a maximum amount of 'n' using a global/shared instance
 */
 func RNG(n int) int {
 	r := lolXD.Get()
-	i := r.Intn(n)
-	lolXD.Put(r)
+	defer lolXD.Put(r)
+	i := 0
+	if n <= 0 {
+		// because panic is just rude.
+		_, _ = os.Stderr.WriteString("RNG: n must be greater than 0, returning 0")
+		return i
+	}
+	if n <= 1<<31-1 {
+		n32 := int32(n)
+		if n32&(n32-1) == 0 {
+			i = int(int32(r.Int63()>>32) & (n32 - 1))
+		}
+		maximum := int32((1 << 31) - 1 - (1<<31)%uint32(n32))
+		v := int32(r.Int63() >> 32)
+		for v > maximum {
+			v = int32(r.Int63() >> 32)
+		}
+		i = int(v % n32)
+	}
 	return i
 }
 
@@ -167,7 +187,7 @@ func randStr(upper bool, size int) string {
 	buf := strBufs.Get()
 	r := lolXD.Get()
 	for i := 0; i != size; i++ {
-		ui32 := int(r.Uint32())
+		ui32 := int(r.Int63() >> 31)
 		switch upper {
 		case true:
 			_ = buf.WriteByte(charsetWithUpper[ui32%len(charsetWithUpper)])

entropy/entropy_test.go

@@ -49,15 +49,15 @@ func Test_RNG(t *testing.T) {
 		t.Errorf("GetSharedRand(55555) returned the same value twice!")
 	}
 	r := AcquireRand()
-	one := r.Intn(55555)
-	two := r.Intn(55555)
+	one := r.Uint64()
+	two := r.Uint64()
 	if one == two {
 		t.Errorf("AcquireRand() returned the same value twice!")
 	}
 	ReleaseRand(r)
 	r = AcquireRand()
-	one1 := r.Intn(55555)
-	two1 := r.Intn(55555)
+	one1 := r.Uint64()
+	two1 := r.Uint64()
 	if one1 == two1 {
 		t.Errorf("AcquireRand() returned the same value twice!")
 	}