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Reduce allocations in ChecksumUtilities.BytesToString #12359

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Merged
merged 3 commits into from
Oct 17, 2025
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Reduce allocations in ChecksumUtilities.BytesToString #12359

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Reduce allocations in ChecksumUtilities.BytesToString
ToddGrun Oct 17, 2025
5f5186c
use var
ToddGrun Oct 17, 2025
dd600a5
1) Use string.Create directly instead of messing around with stackalloc
ToddGrun Oct 17, 2025
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25 changes: 15 additions & 10 deletions src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/ChecksumUtilities.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,8 +3,6 @@

using System;
using System.Collections.Immutable;
using System.Globalization;
using Microsoft.AspNetCore.Razor.PooledObjects;

namespace Microsoft.AspNetCore.Razor.Language;

Expand All @@ -17,15 +15,22 @@ public static string BytesToString(ImmutableArray<byte> bytes)
throw new ArgumentNullException(nameof(bytes));
}

using var _ = StringBuilderPool.GetPooledObject(out var builder);
builder.EnsureCapacity(bytes.Length);

foreach (var b in bytes)
#if NET9_0_OR_GREATER
return Convert.ToHexStringLower(bytes.AsSpan());
#else
return string.Create(bytes.Length * 2, bytes, static (span, bytes) =>
{
// The x2 format means lowercase hex, where each byte is a 2-character string.
builder.Append(b.ToString("x2", CultureInfo.InvariantCulture));
}
foreach (var b in bytes)
{
// Write hex chars directly
span[0] = GetHexChar(b >> 4);
span[1] = GetHexChar(b & 0xf);
span = span[2..];
}
});

return builder.ToString();
static char GetHexChar(int value)
=> (char)(value < 10 ? '0' + value : 'a' + (value - 10));
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@DustinCampbell DustinCampbell Oct 17, 2025

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Is this faster than indexing into a pre-allocated array of chars?

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@ToddGrun ToddGrun Oct 17, 2025

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Probably slightly slower, but I didn't want to duplicate HexConverter.CharToHexLookup, especially as this won't be used OOP once we move to net9

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@DustinCampbell DustinCampbell Oct 17, 2025

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I wouldn't duplicate all of that either! I was just thinking of something like this:

private static char GetHexChar(int value) => s_hexChars[value];

private static readonly char[] s_hexChars = new[] { '0', '1', '2', '3', '4', '5', '6', '7, '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

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@DustinCampbell DustinCampbell Oct 17, 2025

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FWIW, that's definitely into the micro-optimization level. I agree that it's not needed for just netstandard2.0. 👍

#endif
}
}