Unmarshalling float with lots of digits can cause >= 2 allocations per number

We can fix this with a little bit of scratch space.

benchmarks/float_test.go

@@ -0,0 +1,28 @@
+package test
+
+import (
+	"testing"
+
+	jsoniter "github.com/json-iterator/go"
+)
+
+func BenchmarkFloatUnmarshal(b *testing.B) {
+	type floaty struct {
+		A float32
+		B float64
+	}
+
+	data, err := jsoniter.Marshal(floaty{A: 1.111111111111111, B: 1.11111111111111})
+	if err != nil {
+		b.Fatal(err)
+	}
+
+	b.ResetTimer()
+	b.ReportAllocs()
+	var out floaty
+	for i := 0; i < b.N; i++ {
+		if err := jsoniter.Unmarshal(data, &out); err != nil {
+			b.Fatal(err)
+		}
+	}
+}

benchmarks/stream_test.go

@@ -10,7 +10,8 @@ import (
 
 func Benchmark_stream_encode_big_object(b *testing.B) {
 	var buf bytes.Buffer
-	var stream = jsoniter.NewStream(jsoniter.ConfigDefault, &buf, 100)
+	stream := jsoniter.NewStream(jsoniter.ConfigDefault, &buf, 100)
+	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {
 		buf.Reset()
 		stream.Reset(&buf)
@@ -22,13 +23,13 @@ func Benchmark_stream_encode_big_object(b *testing.B) {
 }
 
 func TestEncodeObject(t *testing.T) {
-	var stream = jsoniter.NewStream(jsoniter.ConfigDefault, nil, 100)
+	stream := jsoniter.NewStream(jsoniter.ConfigDefault, nil, 100)
 	encodeObject(stream)
 	if stream.Error != nil {
 		t.Errorf("error encoding a test object: %+v", stream.Error)
 		return
 	}
-	var m = make(map[string]interface{})
+	m := make(map[string]interface{})
 	if err := jsoniter.Unmarshal(stream.Buffer(), &m); err != nil {
 		t.Errorf("error unmarshaling a test object: %+v", err)
 		return

iter.go

@@ -26,8 +26,10 @@ const (
 	ObjectValue
 )
 
-var hexDigits []byte
-var valueTypes []ValueType
+var (
+	hexDigits  []byte
+	valueTypes []ValueType
+)
 
 func init() {
 	hexDigits = make([]byte, 256)
@@ -78,6 +80,7 @@ type Iterator struct {
 	captureStartedAt int
 	captured         []byte
 	Error            error
+	scratch          []byte
 	Attachment       interface{} // open for customized decoder
 }
 

iter_float.go

@@ -11,9 +11,11 @@ import (
 
 var floatDigits []int8
 
-const invalidCharForNumber = int8(-1)
-const endOfNumber = int8(-2)
-const dotInNumber = int8(-3)
+const (
+	invalidCharForNumber = int8(-1)
+	endOfNumber          = int8(-2)
+	dotInNumber          = int8(-3)
+)
 
 func init() {
 	floatDigits = make([]int8, 256)
@@ -66,7 +68,7 @@ func (iter *Iterator) ReadBigInt() (ret *big.Int) {
 	return ret
 }
 
-//ReadFloat32 read float32
+// ReadFloat32 read float32
 func (iter *Iterator) ReadFloat32() (ret float32) {
 	c := iter.nextToken()
 	if c == '-' {
@@ -185,11 +187,39 @@ load_loop:
 	return *(*string)(unsafe.Pointer(&str))
 }
 
+func (iter *Iterator) appendNumber(buf []byte) []byte {
+load_loop:
+	for {
+		for i := iter.head; i < iter.tail; i++ {
+			c := iter.buf[i]
+			switch c {
+			case '+', '-', '.', 'e', 'E', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+				buf = append(buf, c)
+				continue
+			default:
+				iter.head = i
+				break load_loop
+			}
+		}
+		if !iter.loadMore() {
+			break
+		}
+	}
+	if iter.Error != nil && iter.Error != io.EOF {
+		return buf
+	}
+	if len(buf) == 0 {
+		iter.ReportError("readNumberAsString", "invalid number")
+	}
+	return buf
+}
+
 func (iter *Iterator) readFloat32SlowPath() (ret float32) {
-	str := iter.readNumberAsString()
+	iter.scratch = iter.appendNumber(iter.scratch[:0])
 	if iter.Error != nil && iter.Error != io.EOF {
 		return
 	}
+	str := *(*string)(unsafe.Pointer(&iter.scratch))
 	errMsg := validateFloat(str)
 	if errMsg != "" {
 		iter.ReportError("readFloat32SlowPath", errMsg)
@@ -297,10 +327,11 @@ non_decimal_loop:
 }
 
 func (iter *Iterator) readFloat64SlowPath() (ret float64) {
-	str := iter.readNumberAsString()
+	iter.scratch = iter.appendNumber(iter.scratch[:0])
 	if iter.Error != nil && iter.Error != io.EOF {
 		return
 	}
+	str := *(*string)(unsafe.Pointer(&iter.scratch))
 	errMsg := validateFloat(str)
 	if errMsg != "" {
 		iter.ReportError("readFloat64SlowPath", errMsg)