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Remove one string allocation in XmlTextEncoder by using stackalloc span and TryFormat #67005

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TrayanZapryanov wants to merge 1 commit into from
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Remove one string allocation in XmlTextEncoder by using stackalloc span and TryFormat #67005

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26 changes: 17 additions & 9 deletions src/libraries/System.Private.Xml/src/System/Xml/Core/XmlTextEncoder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
Expand Down Expand Up @@ -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];
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@TrayanZapryanov TrayanZapryanov Mar 22, 2022

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I am not sure if 8 is the correct value here.

((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)
Expand All @@ -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(';');
}

Expand Down