From 8d1b3494433b05d9fa635867b5d05cae53587f47 Mon Sep 17 00:00:00 2001
From: Victor Irzak <victor.irzak@zomp.com>
Date: Wed, 14 Oct 2026 09:37:37 -0400
Subject: [PATCH] Avoid per-cell allocations in XmlReaderHelper and
 TryParseCellReference

IsStartElement and GetAttribute allocated a LINQ closure on every call,
and TryParseCellReference allocated a substring for every row number.
---
 .../Helpers/CellReferenceConverter.cs         | 17 ++++++++++++++---
 .../Utils/XmlReaderHelper.cs                  | 19 +++++++++++++++----
 .../Issues/MiniExcelGithubIssuesTests.cs      | 18 ++++++++++++++++++
 3 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/src/MiniExcel.Core/Helpers/CellReferenceConverter.cs b/src/MiniExcel.Core/Helpers/CellReferenceConverter.cs
index 5508fc01..a18c960b 100644
--- a/src/MiniExcel.Core/Helpers/CellReferenceConverter.cs
+++ b/src/MiniExcel.Core/Helpers/CellReferenceConverter.cs
@@ -118,10 +118,21 @@ public static bool TryParseCellReference(string? value, out int column, out int
             return false;
         }
 
-        if (position == 0)
+        if (position == 0 || position == value.Length)
             return false;
 
-        return int.TryParse(value[position..], NumberStyles.None, CultureInfo.InvariantCulture, out row)
-            && row is > 0 and <= MaxRowNumber;
+        // Parsed by hand rather than with int.TryParse on a substring, which allocated for every cell
+        for (; position < value.Length; position++)
+        {
+            var digit = value[position] - '0';
+            row = row * 10 + digit;
+            if (digit is < 0 or > 9 || row > MaxRowNumber)
+            {
+                row = 0;
+                return false;
+            }
+        }
+
+        return row > 0;
     }
 }
diff --git a/src/MiniExcel.OpenXml/Utils/XmlReaderHelper.cs b/src/MiniExcel.OpenXml/Utils/XmlReaderHelper.cs
index dacd9e0b..688a4f16 100644
--- a/src/MiniExcel.OpenXml/Utils/XmlReaderHelper.cs
+++ b/src/MiniExcel.OpenXml/Utils/XmlReaderHelper.cs
@@ -67,16 +67,27 @@ public static async Task SkipToNextSiblingAsync(this XmlReader reader, Cancellat
         }
     }
 
+    // Called for every element and cell, so these loop instead of allocating a LINQ closure per call
     public static bool IsStartElement(this XmlReader reader, string name, params string[] nss)
     {
-        return nss.Any(s => reader.IsStartElement(name, s));
+        foreach (var ns in nss)
+        {
+            if (reader.IsStartElement(name, ns))
+                return true;
+        }
+
+        return false;
     }
 
     public static string? GetAttribute(this XmlReader reader, string name, params string[] nss)
     {
-        return nss
-            .Select(ns => reader.GetAttribute(name, ns))
-            .FirstOrDefault(at => at is not null);
+        foreach (var ns in nss)
+        {
+            if (reader.GetAttribute(name, ns) is { } attribute)
+                return attribute;
+        }
+
+        return null;
     }
 
     // Copied and modified from ExcelDataReader - @MIT License
diff --git a/tests/MiniExcel.OpenXml.Tests/Issues/MiniExcelGithubIssuesTests.cs b/tests/MiniExcel.OpenXml.Tests/Issues/MiniExcelGithubIssuesTests.cs
index b5b1090a..862e821d 100644
--- a/tests/MiniExcel.OpenXml.Tests/Issues/MiniExcelGithubIssuesTests.cs
+++ b/tests/MiniExcel.OpenXml.Tests/Issues/MiniExcelGithubIssuesTests.cs
@@ -35,6 +35,24 @@ public void CellReferenceConverterEnforcesWorksheetLimits()
         Assert.False(CellReferenceConverter.TryParseCellReference("A1048577", out _, out _));
     }
 
+    [Theory]
+    [InlineData("B3", 2, 3)]
+    [InlineData("b03", 2, 3)]
+    [InlineData("A", 0, 0)]
+    [InlineData("A0", 0, 0)]
+    [InlineData("A1x", 0, 0)]
+    [InlineData("A-1", 0, 0)]
+    [InlineData("A99999999999", 0, 0)]
+    public void CellReferenceConverterParsesRowNumbers(string reference, int expectedColumn, int expectedRow)
+    {
+        var parsed = CellReferenceConverter.TryParseCellReference(reference, out var column, out var row);
+
+        Assert.Equal(expectedRow > 0, parsed);
+        Assert.Equal(expectedRow, row);
+        if (parsed)
+            Assert.Equal(expectedColumn, column);
+    }
+
     [Fact]
     public void QueryRangeAcceptsMaximumWorksheetCoordinates()
     {