EXPERIMENTAL: Metal backend (#441)

This is not a continuation of the Metal backend; this is simply bringing
the branch up to date and merging it as-is behind an experiment.

---------

Co-authored-by: Isaac Marovitz <isaacryu@icloud.com>
Co-authored-by: Samuliak <samuliak77@gmail.com>
Co-authored-by: SamoZ256 <96914946+SamoZ256@users.noreply.github.com>
Co-authored-by: Isaac Marovitz <42140194+IsaacMarovitz@users.noreply.github.com>
Co-authored-by: riperiperi <rhy3756547@hotmail.com>
Co-authored-by: Gabriel A <gab.dark.100@gmail.com>

src/Ryujinx.Graphics.Metal/HashTableSlim.cs

@@ -0,0 +1,143 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+
+namespace Ryujinx.Graphics.Metal
+{
+    interface IRefEquatable<T>
+    {
+        bool Equals(ref T other);
+    }
+
+    class HashTableSlim<TKey, TValue> where TKey : IRefEquatable<TKey>
+    {
+        private const int TotalBuckets = 16; // Must be power of 2
+        private const int TotalBucketsMask = TotalBuckets - 1;
+
+        private struct Entry
+        {
+            public int Hash;
+            public TKey Key;
+            public TValue Value;
+        }
+
+        private struct Bucket
+        {
+            public int Length;
+            public Entry[] Entries;
+
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            public readonly Span<Entry> AsSpan()
+            {
+                return Entries == null ? Span<Entry>.Empty : Entries.AsSpan(0, Length);
+            }
+        }
+
+        private readonly Bucket[] _hashTable = new Bucket[TotalBuckets];
+
+        public IEnumerable<TKey> Keys
+        {
+            get
+            {
+                foreach (Bucket bucket in _hashTable)
+                {
+                    for (int i = 0; i < bucket.Length; i++)
+                    {
+                        yield return bucket.Entries[i].Key;
+                    }
+                }
+            }
+        }
+
+        public IEnumerable<TValue> Values
+        {
+            get
+            {
+                foreach (Bucket bucket in _hashTable)
+                {
+                    for (int i = 0; i < bucket.Length; i++)
+                    {
+                        yield return bucket.Entries[i].Value;
+                    }
+                }
+            }
+        }
+
+        public void Add(ref TKey key, TValue value)
+        {
+            var entry = new Entry
+            {
+                Hash = key.GetHashCode(),
+                Key = key,
+                Value = value,
+            };
+
+            int hashCode = key.GetHashCode();
+            int bucketIndex = hashCode & TotalBucketsMask;
+
+            ref var bucket = ref _hashTable[bucketIndex];
+            if (bucket.Entries != null)
+            {
+                int index = bucket.Length;
+
+                if (index >= bucket.Entries.Length)
+                {
+                    Array.Resize(ref bucket.Entries, index + 1);
+                }
+
+                bucket.Entries[index] = entry;
+            }
+            else
+            {
+                bucket.Entries = new[]
+                {
+                    entry,
+                };
+            }
+
+            bucket.Length++;
+        }
+
+        public bool Remove(ref TKey key)
+        {
+            int hashCode = key.GetHashCode();
+
+            ref var bucket = ref _hashTable[hashCode & TotalBucketsMask];
+            var entries = bucket.AsSpan();
+            for (int i = 0; i < entries.Length; i++)
+            {
+                ref var entry = ref entries[i];
+
+                if (entry.Hash == hashCode && entry.Key.Equals(ref key))
+                {
+                    entries[(i + 1)..].CopyTo(entries[i..]);
+                    bucket.Length--;
+
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        public bool TryGetValue(ref TKey key, out TValue value)
+        {
+            int hashCode = key.GetHashCode();
+
+            var entries = _hashTable[hashCode & TotalBucketsMask].AsSpan();
+            for (int i = 0; i < entries.Length; i++)
+            {
+                ref var entry = ref entries[i];
+
+                if (entry.Hash == hashCode && entry.Key.Equals(ref key))
+                {
+                    value = entry.Value;
+                    return true;
+                }
+            }
+
+            value = default;
+            return false;
+        }
+    }
+}