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Cache the column mapping count in CellReferenceConverter #1023

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Merged
michelebastione merged 1 commit into from
Oct 15, 2026
Merged

Cache the column mapping count in CellReferenceConverter #1023

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8 changes: 7 additions & 1 deletion src/MiniExcel.Core/Helpers/CellReferenceConverter.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,10 @@ public static class CellReferenceConverter
private static readonly ConcurrentDictionary<int, string> IntMappingToAlphabet = new();
private static readonly ConcurrentDictionary<string, int> AlphabetMappingToInt = new();

// ConcurrentDictionary.Count takes every internal lock, too slow for a per-cell check.
// Entries are only added, contiguously from 0, so a cached count is safe to read.
private static volatile int _mappedCount;

static CellReferenceConverter()
{
EnsureMappingsUpTo(GeneralColumnIndex);
Expand All @@ -33,7 +37,7 @@ public static int GetNumericalIndex(string? columnName)

private static void EnsureMappingsUpTo(int columnIndex)
{
if (columnIndex < IntMappingToAlphabet.Count)
if (columnIndex < _mappedCount)
return;

if (columnIndex > MaxColumnNumber - 1)
Expand All @@ -46,6 +50,8 @@ private static void EnsureMappingsUpTo(int columnIndex)
IntMappingToAlphabet.TryAdd(i, name);
AlphabetMappingToInt.TryAdd(name, i);
}

_mappedCount = IntMappingToAlphabet.Count;
}

private static string GetColumnFromIndex(int value)
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