implement readFloat32 fast path

2025-06-15 22:50:24 +02:00 · 2017-01-15 17:30:02 +08:00
parent a57c8c6202
commit 5b2a731963
4 changed files with 181 additions and 79 deletions
--- a/feature_iter_float.go
+++ b/feature_iter_float.go
@ -0,0 +1,156 @@
+package jsoniter
+
+import (
+	"io"
+	"strconv"
+	"unsafe"
+)
+
+var zeroToNineDigits []int8
+const invalidCharForNumber = int8(-1)
+const endOfNumber = int8(-2)
+const dotInNumber = int8(-3)
+const safeToMultiple10 = uint64(0xffffffffffffffff) / 10 - 10
+
+func init() {
+	zeroToNineDigits = make([]int8, 256)
+	for i := 0; i < len(zeroToNineDigits); i++ {
+		zeroToNineDigits[i] = invalidCharForNumber
+	}
+	for i := int8('0'); i < int8('9'); i++ {
+		zeroToNineDigits[i] = i - int8('0')
+	}
+	zeroToNineDigits[','] = endOfNumber;
+	zeroToNineDigits[']'] = endOfNumber;
+	zeroToNineDigits['}'] = endOfNumber;
+	zeroToNineDigits[' '] = endOfNumber;
+	zeroToNineDigits['.'] = dotInNumber;
+}
+
+func (iter *Iterator) ReadFloat32() (ret float32) {
+	c := iter.nextToken()
+	if c == '-' {
+		return -iter.readPositiveFloat32()
+	} else {
+		iter.unreadByte()
+		return iter.readPositiveFloat32()
+	}
+}
+
+func (iter *Iterator) readPositiveFloat32() (ret float32) {
+	value := uint64(0)
+	c := byte(' ')
+	i := iter.head
+	non_decimal_loop:
+	for ; i < iter.tail; i++ {
+		c = iter.buf[i]
+		ind := zeroToNineDigits[c]
+		switch ind {
+		case invalidCharForNumber:
+			return iter.readFloat32SlowPath()
+		case endOfNumber:
+			iter.head = i
+			return float32(value)
+		case dotInNumber:
+			break non_decimal_loop
+		}
+		if value > safeToMultiple10 {
+			return iter.readFloat32SlowPath()
+		}
+		value = (value << 3) + (value << 1) + uint64(ind); // value = value * 10 + ind;
+	}
+	if c == '.' {
+		i++
+		decimalPlaces := 0;
+		for ; i < iter.tail; i++ {
+			c = iter.buf[i]
+			ind := zeroToNineDigits[c];
+			switch ind {
+			case endOfNumber:
+				if decimalPlaces > 0 && decimalPlaces < len(POW10) {
+					iter.head = i
+					return float32(float64(value) / float64(POW10[decimalPlaces]))
+				}
+				// too many decimal places
+			return iter.readFloat32SlowPath()
+			case invalidCharForNumber:
+				fallthrough
+			case dotInNumber:
+				return iter.readFloat32SlowPath()
+			}
+			decimalPlaces++
+			if value > safeToMultiple10 {
+				return iter.readFloat32SlowPath()
+			}
+			value = (value << 3) + (value << 1) + uint64(ind)
+		}
+	}
+	return iter.readFloat32SlowPath()
+}
+
+func (iter *Iterator) readFloat32SlowPath() (ret float32) {
+	strBuf := [16]byte{}
+	str := strBuf[0:0]
+	hasMore := true
+	for hasMore {
+		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':
+				str = append(str, c)
+				continue
+			default:
+				hasMore = false
+				break
+			}
+		}
+		if hasMore {
+			if !iter.loadMore() {
+				break
+			}
+		}
+	}
+	if iter.Error != nil && iter.Error != io.EOF {
+		return
+	}
+	val, err := strconv.ParseFloat(*(*string)(unsafe.Pointer(&str)), 32)
+	if err != nil {
+		iter.Error = err
+		return
+	}
+	return float32(val)
+}
+
+// ReadFloat64 reads a json object as Float64
+func (iter *Iterator) ReadFloat64() (ret float64) {
+	strBuf := [8]byte{}
+	str := strBuf[0:0]
+	hasMore := true
+	for hasMore {
+		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':
+				str = append(str, c)
+				continue
+			default:
+				hasMore = false
+				break
+			}
+		}
+		if hasMore {
+			if !iter.loadMore() {
+				break
+			}
+		}
+	}
+	if iter.Error != nil && iter.Error != io.EOF {
+		return
+	}
+	val, err := strconv.ParseFloat(*(*string)(unsafe.Pointer(&str)), 64)
+	if err != nil {
+		iter.Error = err
+		return
+	}
+	return val
+}