From e6347e1e0b410cb4150218d87c46aac343c19956 Mon Sep 17 00:00:00 2001
From: Alexandr Mayorskiy <a.mayorskiy@corp.mail.ru>
Date: Tue, 8 Oct 2019 22:47:07 +0300
Subject: [PATCH] optimize writer

---
 jwriter/writer.go | 43 ++++++++++++++++++++++++++++++-------------
 1 file changed, 30 insertions(+), 13 deletions(-)

diff --git a/jwriter/writer.go b/jwriter/writer.go
index b9ed7cc..eb8547c 100644
--- a/jwriter/writer.go
+++ b/jwriter/writer.go
@@ -270,16 +270,25 @@ func (w *Writer) Bool(v bool) {
 
 const chars = "0123456789abcdef"
 
-func isNotEscapedSingleChar(c byte, escapeHTML bool) bool {
-	// Note: might make sense to use a table if there are more chars to escape. With 4 chars
-	// it benchmarks the same.
-	if escapeHTML {
-		return c != '<' && c != '>' && c != '&' && c != '\\' && c != '"' && c >= 0x20 && c < utf8.RuneSelf
-	} else {
-		return c != '\\' && c != '"' && c >= 0x20 && c < utf8.RuneSelf
+func getTable(falseValues ...int) [128]bool {
+	table := [128]bool{}
+
+	for i := 0; i < 128; i++ {
+		table[i] = true
 	}
+
+	for _, v := range falseValues {
+		table[v] = false
+	}
+
+	return table
 }
 
+var (
+	htmlEscapeTable   = getTable(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, '"', '&', '<', '>', '\\')
+	htmlNoEscapeTable = getTable(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, '"', '\\')
+)
+
 func (w *Writer) String(s string) {
 	w.Buffer.AppendByte('"')
 
@@ -288,15 +297,23 @@ func (w *Writer) String(s string) {
 
 	p := 0 // last non-escape symbol
 
+	var escapeTable [128]bool
+	if w.NoEscapeHTML {
+		escapeTable = htmlNoEscapeTable
+	} else {
+		escapeTable = htmlEscapeTable
+	}
+
 	for i := 0; i < len(s); {
 		c := s[i]
 
-		if isNotEscapedSingleChar(c, !w.NoEscapeHTML) {
-			// single-width character, no escaping is required
-			i++
-			continue
-		} else if c < utf8.RuneSelf {
-			// single-with character, need to escape
+		if c < utf8.RuneSelf {
+			if escapeTable[c] {
+				// single-width character, no escaping is required
+				i++
+				continue
+			}
+
 			w.Buffer.AppendString(s[p:i])
 			switch c {
 			case '\t':