stgsharp/StgSharp.Benchmark/SwissBenchmark.cs

//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="SwissBenchmark"
// Project: StgSharp
// AuthorGroup: Nitload
// Copyright (c) Nitload. All rights reserved.
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using BenchmarkDotNet.Attributes;
using StgSharp.Collections;
using System;
using System.Collections.Generic;

namespace StgSharp.Benchmark
{
    /// <summary>
    ///   Benchmark comparing SwissTable (SSE2 SIMD probing, zero-GC, native memory) against <see
    ///   cref="Dictionary{TKey, TValue}" /> for the L4 cache address mapping workload: concentrated
    ///   small-key insert/lookup/remove cycles.  <para> SwissTable.Create() performs a 1 MB memset
    ///   (65536 × 16 control bytes), which is separated into IterationSetup to avoid polluting
    ///   insert timings.</para>
    /// </summary>
    [MemoryDiagnoser]
    public class SwissTableBench
    {

        private const int LookupCount = 4096;

        private nint[] _lookupKeys = null!;

        // ── Pre-generated key arrays ──

        private nint[] _preloadedKeys = null!;
        private Dictionary<nint, nint> _dictLookup = null!;
        private Dictionary<nint, nint> _freshDict = null!;

        // ── Fresh instances for insert/mixed (rebuilt each iteration) ──

        private SwissTable _freshSwiss = null!;

        // ── Lookup targets (pre-filled in GlobalSetup) ──

        private SwissTable _swissLookup = null!;

        [Params(500, 2000, 5000)]
        public int KeyCount;

        [GlobalCleanup]
        public void Cleanup()
        {
            _dictLookup.Clear();
            _dictLookup.TrimExcess();
        }

        // ══════════════════════════════════════
        // Insert: pure write throughput
        // Empty table → fill N keys
        // Create() cost excluded via IterationSetup
        // ══════════════════════════════════════

        [Benchmark]
        public void Dictionary_Insert()
        {
            Dictionary<nint, nint> dict = _freshDict;
            nint[] keys = _preloadedKeys;
            for (int i = 0; i < keys.Length; i++) {
                dict[keys[i]] = keys[i] * 2;
            }
        }

        // ══════════════════════════════════════
        // Lookup: pure read throughput
        // Pre-filled table, random key access
        // ══════════════════════════════════════

        [Benchmark(Baseline = true)]
        public nint Dictionary_Lookup()
        {
            nint sum = 0;
            nint[] keys = _lookupKeys;
            Dictionary<nint, nint> dict = _dictLookup;
            for (int i = 0; i < keys.Length; i++)
            {
                if (dict.TryGetValue(keys[i], out nint value)) {
                    sum += value;
                }
            }
            return sum;
        }

        // ══════════════════════════════════════
        // Mixed: insert all → lookup half → remove half → lookup all
        // Simulates L4 cache lifecycle:
        // load working set → compute → evict → recompute
        // ══════════════════════════════════════

        [Benchmark]
        public nint Dictionary_Mixed()
        {
            Dictionary<nint, nint> dict = _freshDict;
            nint[] keys = _preloadedKeys;
            nint sum = 0;

            // insert all
            for (int i = 0; i < keys.Length; i++)
            {
                dict[keys[i]] = keys[i] * 2;
            }

            // lookup first half
            for (int i = 0; i < keys.Length / 2; i++)
            {
                if (dict.TryGetValue(keys[i], out nint value)) {
                    sum += value;
                }
            }

            // remove first half (eviction)
            for (int i = 0; i < keys.Length / 2; i++)
            {
                dict.Remove(keys[i]);
            }

            // lookup all (half hit, half miss)
            for (int i = 0; i < keys.Length; i++)
            {
                if (dict.TryGetValue(keys[i], out nint value)) {
                    sum += value;
                }
            }

            return sum;
        }

        [IterationSetup(Targets = [
            nameof(SwissTable_Insert),
            nameof(SwissTable_Mixed),
            nameof(Dictionary_Insert),
            nameof(Dictionary_Mixed)
        ])]
        public void IterationSetup()
        {
            _freshSwiss = SwissTable.Create();
            _freshDict = new Dictionary<nint, nint>(KeyCount);
        }

        // ── Setup / Teardown ──

        [GlobalSetup]
        public void Setup()
        {
            _preloadedKeys = new nint[KeyCount];
            _lookupKeys = new nint[LookupCount];

            _swissLookup = SwissTable.Create();
            _dictLookup = new Dictionary<nint, nint>(KeyCount);

            for (int i = 0; i < KeyCount; i++)
            {
                _preloadedKeys[i] = (nint)i;
                _swissLookup.TryAddOrSet((nint)i, (nint)(i * 2), out _);
                _dictLookup[(nint)i] = (nint)(i * 2);
            }

            Random rng = new Random(42);
            for (int i = 0; i < LookupCount; i++) {
                _lookupKeys[i] = (nint)rng.Next(0, KeyCount);
            }
        }

        [Benchmark]
        public void SwissTable_Insert()
        {
            SwissTable swiss = _freshSwiss;
            nint[] keys = _preloadedKeys;
            for (int i = 0; i < keys.Length; i++) {
                swiss.TryAddOrSet(keys[i], keys[i] * 2, out _);
            }
        }

        [Benchmark]
        public nint SwissTable_Lookup()
        {
            nint sum = 0;
            nint[] keys = _lookupKeys;
            SwissTable swiss = _swissLookup;
            for (int i = 0; i < keys.Length; i++)
            {
                if (swiss.TryGet(keys[i], out nint value)) {
                    sum += value;
                }
            }
            return sum;
        }

        [Benchmark]
        public nint SwissTable_Mixed()
        {
            SwissTable swiss = _freshSwiss;
            nint[] keys = _preloadedKeys;
            nint sum = 0;

            // insert all
            for (int i = 0; i < keys.Length; i++)
            {
                swiss.TryAddOrSet(keys[i], keys[i] * 2, out _);
            }

            // lookup first half
            for (int i = 0; i < keys.Length / 2; i++)
            {
                if (swiss.TryGet(keys[i], out nint value)) {
                    sum += value;
                }
            }

            // remove first half (eviction)
            for (int i = 0; i < keys.Length / 2; i++)
            {
                swiss.TryRemove(keys[i], out _);
            }

            // lookup all (half hit, half miss)
            for (int i = 0; i < keys.Length; i++)
            {
                if (swiss.TryGet(keys[i], out nint value)) {
                    sum += value;
                }
            }

            return sum;
        }

    }
}