From 551b10d7f2a42e36b518ba4c897f4f852df81de3 Mon Sep 17 00:00:00 2001
From: Traian Zaprianov <Traian.Zaprianov@docuware.com>
Date: Tue, 22 Mar 2022 19:45:01 +0200
Subject: [PATCH] Replace several int.ToString("X",
 NumberFormatInfo.InvariantInfo) by using stackalloc char[] and Tryformat

---
 .../src/System/Xml/Core/XmlTextEncoder.cs     | 26 ++++++++++++-------
 1 file changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextEncoder.cs b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextEncoder.cs
index 52d924a6c491df..cd5e098015cd3f 100644
--- a/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextEncoder.cs
+++ b/src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextEncoder.cs
@@ -239,9 +239,7 @@ internal void WriteSurrogateCharEntity(char lowChar, char highChar)
                 _attrValue.Append(lowChar);
             }
 
-            _textWriter.Write("&#x");
-            _textWriter.Write(surrogateChar.ToString("X", NumberFormatInfo.InvariantInfo));
-            _textWriter.Write(';');
+            WriteIntEntityImpl(surrogateChar);
         }
 
         internal void Write(ReadOnlySpan<char> text)
@@ -477,16 +475,17 @@ internal void WriteCharEntity(char ch)
                 throw new ArgumentException(SR.Xml_InvalidSurrogateMissingLowChar);
             }
 
-            string strVal = ((int)ch).ToString("X", NumberFormatInfo.InvariantInfo);
+            Span<char> chAsSpan = stackalloc char[8];
+            ((int)ch).TryFormat(chAsSpan, out int charsWritten, "X", NumberFormatInfo.InvariantInfo);
             if (_cacheAttrValue)
             {
                 Debug.Assert(_attrValue != null);
                 _attrValue.Append("&#x");
-                _attrValue.Append(strVal);
+                _attrValue.Append(chAsSpan.Slice(0, charsWritten));
                 _attrValue.Append(';');
             }
 
-            WriteCharEntityImpl(strVal);
+            WriteCharEntityImpl(chAsSpan.Slice(0, charsWritten));
         }
 
         internal void WriteEntityRef(string name)
@@ -508,13 +507,22 @@ internal void WriteEntityRef(string name)
 
         private void WriteCharEntityImpl(char ch)
         {
-            WriteCharEntityImpl(((int)ch).ToString("X", NumberFormatInfo.InvariantInfo));
+            WriteIntEntityImpl(ch);
+        }
+
+        private void WriteIntEntityImpl(int value)
+        {
+            Span<char> chAsSpan = stackalloc char[8];
+            if (value.TryFormat(chAsSpan, out int charsWritten, "X", NumberFormatInfo.InvariantInfo))
+                WriteCharEntityImpl(chAsSpan.Slice(0, charsWritten));
+            else
+                WriteCharEntityImpl(value.ToString("X", NumberFormatInfo.InvariantInfo));
         }
 
-        private void WriteCharEntityImpl(string strVal)
+        private void WriteCharEntityImpl(ReadOnlySpan<char> strSpan)
         {
             _textWriter.Write("&#x");
-            _textWriter.Write(strVal);
+            _textWriter.Write(strSpan);
             _textWriter.Write(';');
         }