make skipWhitespaces faster

jsoniter.go

@@ -72,16 +72,20 @@ func ParseString(input string) *Iterator {
 }
 
 func (iter *Iterator) skipWhitespaces() {
-	c := iter.readByte()
 	for {
+		for i := iter.head; i < iter.tail; i++ {
+			c := iter.buf[i]
 			switch c {
 			case ' ', '\n', '\t', 'r':
-			c = iter.readByte()
 				continue
 			}
-		break
+			iter.head = i
+			return
+		}
+		if !iter.loadMore() {
+			return
+		}
 	}
-	iter.unreadByte()
 }
 
 func (iter *Iterator) ReportError(operation string, msg string) {
@@ -107,16 +111,28 @@ func (iter *Iterator) CurrentBuffer() string {
 
 func (iter *Iterator) readByte() (ret byte) {
 	if iter.head == iter.tail {
+		if iter.loadMore() {
+			ret = iter.buf[iter.head]
+			iter.head++
+			return ret
+		}
+	}
+	ret = iter.buf[iter.head]
+	iter.head++
+	return ret
+}
+
+func (iter *Iterator) loadMore() bool {
 	if iter.reader == nil {
 		iter.Error = io.EOF
-			return
+		return false
 	}
 	for {
 		n, err := iter.reader.Read(iter.buf)
 		if n == 0 {
 			if err != nil {
 				iter.Error = err
-					return
+				return false
 			} else {
 				// n == 0, err == nil is not EOF
 				continue
@@ -124,13 +140,9 @@ func (iter *Iterator) readByte() (ret byte) {
 		} else {
 			iter.head = 0
 			iter.tail = n
-				break
+			return true
 		}
 	}
-	}
-	ret = iter.buf[iter.head]
-	iter.head++
-	return ret
 }
 
 func (iter *Iterator) unreadByte() {
@@ -314,7 +326,7 @@ func (iter *Iterator) ReadStringAsBytes() (ret []byte) {
 		iter.ReportError("ReadString", `expects " or n`)
 		return
 	}
-	end, escaped := stringEnd(iter.buf[iter.head:])
+	end, escaped := stringEnd(iter.buf[iter.head:iter.tail])
 	if end != -1 && !escaped {
 		ret = iter.buf[iter.head:iter.head+end-1]
 		iter.head += end