Corvus Low Alloc Data Structures

What it does

When your agent uses it

• : choosing which stack-allocated collection to use
• Writing new ref-struct types
• Adding SIMD-accelerated code paths
• Understanding branchless techniques

Example prompts

• “/corvus-low-alloc-data-structures”

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

1. 1Accept initial storage as constructor parameters — let the caller stackalloc the initial buffers
2. 2Define stack-alloc size constants on the type (e.g., StackAllocBucketSize)
3. 3Implement IDisposable to return any ArrayPool-rented overflow buffers
4. 4Use MemoryMarshal.Write/Read with [MethodImpl(AggressiveInlining)] for packed entries
5. 5Growth via ArrayPool.Shared.Rent() with geometric (2×) sizing
6. 6Return old rented buffer before taking a new one during growth

What it can do on your machine

Read from SKILL.md and the folder at commit b9e3040. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are csharp).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Corvus Low Alloc Data Structures loads about 2.6k tokens when it runs. Until then it costs about 181 tokens; SKILL.md has 763 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~181

When it runs · the whole SKILL.md, loaded when a task matches

~2.6k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from corvus-dotnet/Corvus.JsonSchema at commit b9e3040, republished under its Apache-2.0 licence (© corvus-dotnet). 763 words, ~2,555 tokens.

name

corvus-low-alloc-data-structures

description

Use and extend the custom low-allocation data structures in Corvus.JsonSchema. Covers ref-struct collections (Utf8KeyHashSet, UniqueItemsHashSet, ValueListBuilder, ValueStringBuilder, Utf8ValueStringBuilder, BitStack, Sequence), SIMD scanning patterns, bit manipulation tricks, and happy-path optimisations like lazy error messages. USE FOR: choosing which stack-allocated collection to use, writing new ref-struct types, adding SIMD-accelerated code paths, understanding branchless techniques, writing validation code that avoids allocation on success. DO NOT USE FOR: basic buffer allocation patterns (use corvus-buffer-and-pooling), document model (use corvus-parsed-documents-and-memory).

// Typical usage — stack-allocate initial buffers, dispose to return any rented overflow
Span<int> buckets = stackalloc int[Utf8KeyHashSet.StackAllocBucketSize];
Span<byte> entries = stackalloc byte[Utf8KeyHashSet.StackAllocEntrySize];
Span<byte> keyBuffer = stackalloc byte[Utf8KeyHashSet.StackAllocKeyBufferSize];

using Utf8KeyHashSet hashSet = new(estimatedPropertyCount, buckets, entries, keyBuffer);
bool added = hashSet.Add(utf8Key);

Span<int> initialBuffer = stackalloc int[16];
ValueListBuilder<int> list = new(initialBuffer);

try
{
    list.Append(42);
    list.Append(99);
    ReadOnlySpan<int> items = list.AsSpan();
}
finally
{
    list.Dispose();  // returns any rented array
}

// UTF-16 string building
Span<char> initialChars = stackalloc char[JsonConstants.StackallocCharThreshold];
ValueStringBuilder sb = new(initialChars);
try
{
    sb.Append("hello");
    sb.Append(' ');
    sb.Append("world");
    return sb.ToString();
}
finally
{
    sb.Dispose();
}

// UTF-8 string building
Span<byte> initialBytes = stackalloc byte[JsonConstants.StackallocByteThreshold];
Utf8ValueStringBuilder usb = new(initialBytes);
try
{
    usb.Append("hello"u8);
    ReadOnlySpan<byte> result = usb.AsSpan();
}
finally
{
    usb.Dispose();
}

BitStack stack = default;
stack.PushTrue();   // entering an object
stack.PushFalse();  // entering an array
bool wasObject = stack.Pop();  // leaving — returns true if it was an object

Layout (32 bytes):
  object? payload     (8 bytes)  — reference-type backing for multi-value
  double rawValue     (8 bytes)  — inline double storage
  JsonElement single  (12 bytes) — inline singleton element
  int countAndTag     (4 bytes)  — bits 0-23: count, bits 24-31: tag

if (Vector.IsHardwareAccelerated && length >= Vector<byte>.Count * 2)
{
    Vector<byte> vQuote = new((byte)'"');
    Vector<byte> vBackslash = new((byte)'\\');
    Vector<byte> vControlMax = new(0x1F);

    Vector<byte> vData = Unsafe.ReadUnaligned<Vector<byte>>(
        ref Unsafe.AddByteOffset(ref searchSpace, index));

    var vMatches = Vector.BitwiseOr(
        Vector.BitwiseOr(
            Vector.Equals(vData, vQuote),
            Vector.Equals(vData, vBackslash)),
        Vector.LessThan(vData, vControlMax));
}

ulong powerOfTwoFlag = match ^ (match - 1);    // isolate lowest set bit
return (int)((powerOfTwoFlag * XorPowerOfTwoToHighByte) >> 57);

public static bool IsTokenTypePrimitive(JsonTokenType tokenType) =>
    (tokenType - JsonTokenType.String) <= (JsonTokenType.Null - JsonTokenType.String);

private static readonly JsonSchemaMessageProvider ExpectedDate =
    static (buffer, out written) => { /* format error message only when called */ };

© corvus-dotnet, Apache-2.0. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

Just SKILL.md in .github/skills/corvus-low-alloc-data-structures of corvus-dotnet/Corvus.JsonSchema.

Open the folder on GitHubat commit b9e3040