Optimize randBool() and randString() (#41)

* - Optimize the randBool() function.

  Previous time: 15.175 ns/op
  New time:      4.78 ns/op

* - Optimize randString() by using strings.Builder.
  30% less memory used and a 5 to 7% higher throughput.

* - Add benchmarks for randBool() and randString().

* - Ran go fmt

fuzz.go

@@ -24,6 +24,7 @@ import (
 	"time"
 
 	"github.com/google/gofuzz/bytesource"
+	"strings"
 )
 
 // fuzzFuncMap is a map from a type to a fuzzFunc that handles that type.
@@ -495,10 +496,7 @@ var fillFuncMap = map[reflect.Kind]func(reflect.Value, *rand.Rand){
 
 // randBool returns true or false randomly.
 func randBool(r *rand.Rand) bool {
-	if r.Int()&1 == 1 {
-		return true
-	}
-	return false
+	return r.Int31()&(1<<30) == 0
 }
 
 type int63nPicker interface {
@@ -526,11 +524,12 @@ var unicodeRanges = []charRange{
 // may include a variety of (valid) UTF-8 encodings.
 func randString(r *rand.Rand) string {
 	n := r.Intn(20)
-	runes := make([]rune, n)
-	for i := range runes {
-		runes[i] = unicodeRanges[r.Intn(len(unicodeRanges))].choose(r)
+	sb := strings.Builder{}
+	sb.Grow(n)
+	for i := 0; i < n; i++ {
+		sb.WriteRune(unicodeRanges[r.Intn(len(unicodeRanges))].choose(r))
 	}
-	return string(runes)
+	return sb.String()
 }
 
 // randUint64 makes random 64 bit numbers.

fuzz_test.go

@@ -528,9 +528,12 @@ type customInt63 struct {
 
 func (c customInt63) Int63n(n int64) int64 {
 	switch c.mode {
-	case modeFirst: return 0
-	case modeLast: return n-1
-	default: return rand.Int63n(n)
+	case modeFirst:
+		return 0
+	case modeLast:
+		return n - 1
+	default:
+		return rand.Int63n(n)
 	}
 }
 
@@ -566,3 +569,19 @@ func TestNewFromGoFuzz(t *testing.T) {
 		t.Errorf("Fuzz(%q) = %d, want: %d", input, got, want)
 	}
 }
+
+func BenchmarkRandBool(b *testing.B) {
+	rs := rand.New(rand.NewSource(123))
+
+	for i := 0; i < b.N; i++ {
+		randBool(rs)
+	}
+}
+
+func BenchmarkRandString(b *testing.B) {
+	rs := rand.New(rand.NewSource(123))
+
+	for i := 0; i < b.N; i++ {
+		randString(rs)
+	}
+}