base 64 Id generator

* < 50% allocations

BenchmarkUint64ToId-8        	50000000	        30.6 ns/op	       7 B/op	       1 allocs/op
BenchmarkUint64ToString2-8   	20000000	       125 ns/op	      63 B/op	       2 allocs/op

actor/process_registry.go

@@ -1,7 +1,6 @@
 package actor
 
 import (
-	"strconv"
 	"sync/atomic"
 
 	cmap "github.com/orcaman/concurrent-map"
@@ -26,13 +25,33 @@ type HostResolver func(*PID) (ActorRef, bool)
 
 func (pr *ProcessRegistryValue) RegisterHostResolver(handler HostResolver) {
 	pr.RemoteHandlers = append(pr.RemoteHandlers, handler)
+}
+
+const (
+	digits = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ~+"
+)
+
+func uint64ToId(u uint64) string {
+	var buf [13]byte
+	i := 13
+	// base is power of 2: use shifts and masks instead of / and %
+	for u >= 64 {
+		i--
+		buf[i] = digits[uintptr(u)&0x3f]
+		u >>= 6
+	}
+	// u < base
+	i--
+	buf[i] = digits[uintptr(u)]
+	i--
+	buf[i] = '$'
 
+	return string(buf[i:])
 }
 
 func (pr *ProcessRegistryValue) getAutoId() string {
 	counter := atomic.AddUint64(&pr.SequenceID, 1)
-	id := "$" + strconv.FormatUint(counter, 16)
-	return id
+	return uint64ToId(counter)
 }
 
 func (pr *ProcessRegistryValue) add(actorRef ActorRef, id string) (*PID, bool) {

actor/process_registry_test.go

@@ -0,0 +1,47 @@
+package actor
+
+import (
+	"strconv"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUint64ToId(t *testing.T) {
+	cases := []struct {
+		i uint64
+		e string
+	}{
+		{0xfedcba9876543210, "$fXsKFxSl38g"},
+		{0x0, "$0"},
+		{0x1, "$1"},
+		{0xf, "$f"},
+		{0x1041041041041041, "$11111111111"},
+	}
+	for _, tc := range cases {
+		t.Run(tc.e, func(t *testing.T) {
+			s := uint64ToId(tc.i)
+			assert.Equal(t, tc.e, s)
+		})
+	}
+
+}
+
+var ss string
+
+func BenchmarkUint64ToId(b *testing.B) {
+	var s string
+	for i := 0; i < b.N; i++ {
+		s = uint64ToId(uint64(i)<<5)
+	}
+	ss = s
+}
+
+func BenchmarkUint64ToString2(b *testing.B) {
+	var s string
+	var buf [12]byte
+	for i := 0; i < b.N; i++ {
+		s = string(strconv.AppendUint(buf[:], uint64(i)<<5, 36))
+	}
+	ss = s
+}