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Merged
SimonCropp merged 1 commit into from
Jun 29, 2026
Merged

Optimize StringBuilder.Equals(ReadOnlySpan<char>) to compare by chunk #565

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8 changes: 4 additions & 4 deletions assemblySize.include.md
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Original file line number Diff line number Diff line change
Expand Up @@ -4,12 +4,12 @@
|----------------|----------------|---------------|-----------|-----------|--------------------|---------------------|-------------|
| netstandard2.0 | 8.0KB | 351.5KB | +343.5KB | +9.5KB | +6.5KB | +9.5KB | +14.0KB |
| netstandard2.1 | 8.5KB | 306.0KB | +297.5KB | +8.5KB | +6.0KB | +9.0KB | +13.5KB |
| net461 | 8.5KB | 350.5KB | +342.0KB | +9.0KB | +6.0KB | +9.0KB | +13.5KB |
| net461 | 8.5KB | 350.5KB | +342.0KB | +9.0KB | +6.5KB | +9.0KB | +13.5KB |
| net462 | 7.0KB | 354.0KB | +347.0KB | +9.0KB | +6.5KB | +9.0KB | +13.5KB |
| net47 | 7.0KB | 353.5KB | +346.5KB | +9.0KB | +6.5KB | +9.5KB | +13.5KB |
| net471 | 8.5KB | 353.0KB | +344.5KB | +9.0KB | +6.0KB | +9.0KB | +13.5KB |
| net472 | 8.5KB | 351.5KB | +343.0KB | +9.0KB | +6.5KB | +9.0KB | +14.0KB |
| net48 | 8.5KB | 351.5KB | +343.0KB | +9.0KB | +6.5KB | +9.0KB | +13.5KB |
| net48 | 8.5KB | 351.5KB | +343.0KB | +9.0KB | +6.5KB | +9.0KB | +14.0KB |
| net481 | 8.5KB | 351.5KB | +343.0KB | +9.0KB | +6.5KB | +9.0KB | +14.0KB |
| netcoreapp2.0 | 9.0KB | 327.5KB | +318.5KB | +9.0KB | +6.5KB | +9.0KB | +13.5KB |
| netcoreapp2.1 | 9.0KB | 308.0KB | +299.0KB | +9.0KB | +6.5KB | +9.0KB | +14.0KB |
Expand All @@ -31,12 +31,12 @@
|----------------|----------------|---------------|-----------|-----------|--------------------|---------------------|-------------|
| netstandard2.0 | 8.0KB | 513.4KB | +505.4KB | +17.2KB | +8.2KB | +14.4KB | +19.4KB |
| netstandard2.1 | 8.5KB | 441.7KB | +433.2KB | +16.2KB | +7.7KB | +13.9KB | +18.9KB |
| net461 | 8.5KB | 513.5KB | +505.0KB | +16.7KB | +7.7KB | +13.9KB | +18.9KB |
| net461 | 8.5KB | 513.5KB | +505.0KB | +16.7KB | +8.2KB | +13.9KB | +18.9KB |
| net462 | 7.0KB | 517.0KB | +510.0KB | +16.7KB | +8.2KB | +13.9KB | +18.9KB |
| net47 | 7.0KB | 516.2KB | +509.2KB | +16.7KB | +8.2KB | +14.4KB | +18.9KB |
| net471 | 8.5KB | 515.4KB | +506.9KB | +16.7KB | +7.7KB | +13.9KB | +18.9KB |
| net472 | 8.5KB | 512.8KB | +504.3KB | +16.7KB | +8.2KB | +13.9KB | +19.4KB |
| net48 | 8.5KB | 512.8KB | +504.3KB | +16.7KB | +8.2KB | +13.9KB | +18.9KB |
| net48 | 8.5KB | 512.8KB | +504.3KB | +16.7KB | +8.2KB | +13.9KB | +19.4KB |
| net481 | 8.5KB | 512.8KB | +504.3KB | +16.7KB | +8.2KB | +13.9KB | +19.4KB |
| netcoreapp2.0 | 9.0KB | 478.9KB | +469.9KB | +16.7KB | +8.2KB | +13.9KB | +18.9KB |
| netcoreapp2.1 | 9.0KB | 447.4KB | +438.4KB | +16.7KB | +8.2KB | +13.9KB | +19.4KB |
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11 changes: 7 additions & 4 deletions src/Polyfill/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,14 +19,17 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
return false;
}

for (var index = 0; index < target.Length; index++)
// Walk the contiguous chunks and compare each with the vectorized SequenceEqual,
// rather than indexing the StringBuilder per char (which walks the chunk list on every access).
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}

span = span.Slice(chunkSpan.Length);
}

return true;
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8 changes: 4 additions & 4 deletions src/Split/net461/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
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8 changes: 4 additions & 4 deletions src/Split/net462/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
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8 changes: 4 additions & 4 deletions src/Split/net47/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
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8 changes: 4 additions & 4 deletions src/Split/net471/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
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8 changes: 4 additions & 4 deletions src/Split/net472/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
Expand Down
8 changes: 4 additions & 4 deletions src/Split/net48/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
Expand Down
8 changes: 4 additions & 4 deletions src/Split/net481/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
Expand Down
8 changes: 4 additions & 4 deletions src/Split/netcoreapp2.0/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
Expand Down
8 changes: 4 additions & 4 deletions src/Split/netstandard2.0/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
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8 changes: 4 additions & 4 deletions src/Split/uap10.0/Polyfill_StringBuilder.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -16,14 +16,14 @@ public static bool Equals(this StringBuilder target, ReadOnlySpan<char> span)
{
return false;
}
for (var index = 0; index < target.Length; index++)
foreach (var chunk in target.GetChunks())
{
var ch1 = target[index];
var ch2 = span[index];
if (ch1 != ch2)
var chunkSpan = chunk.Span;
if (!chunkSpan.SequenceEqual(span.Slice(0, chunkSpan.Length)))
{
return false;
}
span = span.Slice(chunkSpan.Length);
}
return true;
}
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23 changes: 23 additions & 0 deletions src/Tests/PolyfillTests_Memory.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -527,5 +527,28 @@ public async Task StringEqualsSpan()
{
var builder = new StringBuilder("value");
await Assert.That(builder.Equals("value".AsSpan())).IsTrue();
await Assert.That(builder.Equals("other".AsSpan())).IsFalse();
await Assert.That(builder.Equals("val".AsSpan())).IsFalse();
await Assert.That(builder.Equals("values".AsSpan())).IsFalse();
await Assert.That(builder.Equals("".AsSpan())).IsFalse();
await Assert.That(new StringBuilder().Equals("".AsSpan())).IsTrue();
}

[Test]
public async Task StringEqualsSpanMultipleChunks()
{
// A small initial capacity followed by appends past it forces the
// StringBuilder to span multiple chunks, exercising the chunk-walking path.
var builder = new StringBuilder("a", 1);
builder.Append("bb");
builder.Append("ccc");

await Assert.That(builder.Equals("abbccc".AsSpan())).IsTrue();
// mismatch in the first chunk
await Assert.That(builder.Equals("xbbccc".AsSpan())).IsFalse();
// mismatch in a later chunk, after the span has advanced across a chunk boundary
await Assert.That(builder.Equals("abbcxc".AsSpan())).IsFalse();
// matching prefix but wrong length
await Assert.That(builder.Equals("abbcc".AsSpan())).IsFalse();
}
}
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