From 097a3655282846f4f8769e1db698e5506a5c954b Mon Sep 17 00:00:00 2001
From: wreng <mr-wrench@yandex.ru>
Date: Sun, 18 Feb 2024 20:37:11 +0300
Subject: [PATCH] CyclicBuffer optimizations

---
 src/DotRecast.Core/Buffers/RcCyclicBuffer.cs  | 63 +++++++++++++------
 src/DotRecast.Core/Buffers/RcCyclicBuffers.cs | 14 +++--
 .../DotRecast.Core.Test/RcCyclicBufferTest.cs | 41 +++++++++++-
 3 files changed, 93 insertions(+), 25 deletions(-)

diff --git a/src/DotRecast.Core/Buffers/RcCyclicBuffer.cs b/src/DotRecast.Core/Buffers/RcCyclicBuffer.cs
index 2846bfb..65f9a91 100644
--- a/src/DotRecast.Core/Buffers/RcCyclicBuffer.cs
+++ b/src/DotRecast.Core/Buffers/RcCyclicBuffer.cs
@@ -1,12 +1,47 @@
 using System;
+using System.Collections;
 using System.Collections.Generic;
 using System.Net.Security;
 
 namespace DotRecast.Core.Buffers
 {
     // https://github.com/joaoportela/CircularBuffer-CSharp/blob/master/CircularBuffer/CircularBuffer.cs
-    public class RcCyclicBuffer<T>
+    public class RcCyclicBuffer<T> : IEnumerable<T>
     {
+        public struct Enumerator : IEnumerator<T>
+        {
+            private readonly RcCyclicBuffer<T> _buffer;
+            private int _index;
+            private readonly int _size;
+
+            internal Enumerator(RcCyclicBuffer<T> buffer)
+            {
+                _buffer = buffer;
+                _size = _buffer._size;
+                _index = default;
+                Reset();
+            }
+            
+            public bool MoveNext()
+            {
+                return ++_index < _size;
+            }
+
+            public void Reset()
+            {
+                _index = -1;
+            }
+
+            public T Current => _buffer[_index];
+
+            object IEnumerator.Current => Current;
+
+            public void Dispose()
+            {
+                // This could be used to unlock write access to collection
+            }
+        }
+        
         private readonly T[] _buffer;
 
         private int _start;
@@ -155,29 +190,15 @@ namespace DotRecast.Core.Buffers
 
         public T[] ToArray()
         {
-            int idx = 0;
             T[] newArray = new T[Size];
 
-            ForEach(x => newArray[idx++] = x);
+            var span1 = ArrayOne();
+            span1.CopyTo(newArray.AsSpan());
+            ArrayTwo().CopyTo(newArray.AsSpan(span1.Length..));
 
             return newArray;
         }
 
-        public void ForEach(Action<T> action)
-        {
-            var spanOne = ArrayOne();
-            foreach (var item in spanOne)
-            {
-                action.Invoke(item);
-            }
-
-            var spanTwo = ArrayTwo();
-            foreach (var item in spanTwo)
-            {
-                action.Invoke(item);
-            }
-        }
-
         private void ThrowIfEmpty(string message = "Cannot access an empty buffer.")
         {
             if (IsEmpty)
@@ -240,5 +261,11 @@ namespace DotRecast.Core.Buffers
 
             return new Span<T>(_buffer, 0, _end);
         }
+
+        public Enumerator GetEnumerator() => new Enumerator(this);
+        
+        IEnumerator<T> IEnumerable<T>.GetEnumerator() => GetEnumerator();
+        
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
     }
 }
\ No newline at end of file
diff --git a/src/DotRecast.Core/Buffers/RcCyclicBuffers.cs b/src/DotRecast.Core/Buffers/RcCyclicBuffers.cs
index cadcf48..5c8000c 100644
--- a/src/DotRecast.Core/Buffers/RcCyclicBuffers.cs
+++ b/src/DotRecast.Core/Buffers/RcCyclicBuffers.cs
@@ -7,7 +7,11 @@
             long sum = 0;
             checked
             {
-                source.ForEach(x => sum += x);
+                // NOTE: SIMD would be nice here
+                foreach (var x in source)
+                {
+                    sum += x;
+                }
             }
 
             return sum;
@@ -27,11 +31,11 @@
                 return 0;
             
             long minValue = long.MaxValue;
-            source.ForEach(x =>
+            foreach (var x in source)
             {
                 if (x < minValue)
                     minValue = x;
-            });
+            }
 
             return minValue;
         }
@@ -42,11 +46,11 @@
                 return 0;
             
             long maxValue = long.MinValue;
-            source.ForEach(x =>
+            foreach (var x in source)
             {
                 if (x > maxValue)
                     maxValue = x;
-            });
+            }
 
             return maxValue;
         }
diff --git a/test/DotRecast.Core.Test/RcCyclicBufferTest.cs b/test/DotRecast.Core.Test/RcCyclicBufferTest.cs
index 56a9c54..9c72e51 100644
--- a/test/DotRecast.Core.Test/RcCyclicBufferTest.cs
+++ b/test/DotRecast.Core.Test/RcCyclicBufferTest.cs
@@ -1,5 +1,6 @@
 using System;
 using DotRecast.Core.Buffers;
+using DotRecast.Core.Collections;
 using NUnit.Framework;
 
 namespace DotRecast.Core.Test;
@@ -39,11 +40,11 @@ public class RcCyclicBufferTests
         var buffer = new RcCyclicBuffer<int>(5, new[] { 0, 1, 2, 3 });
 
         int x = 0;
-        buffer.ForEach(item =>
+        foreach (var item in buffer)
         {
             Assert.That(item, Is.EqualTo(x));
             x++;
-        });
+        }
     }
 
     [Test]
@@ -290,4 +291,40 @@ public class RcCyclicBufferTests
             Assert.That(buffer[i], Is.EqualTo(i));
         }
     }
+    
+    [Test]
+    public void RcCyclicBuffer_RegularForEachWorks()
+    {
+        var refValues = new[] { 4, 3, 2, 1, 0 };
+        var buffer = new RcCyclicBuffer<int>(5, refValues);
+
+        var index = 0;
+        foreach (var element in buffer)
+        {
+            Assert.That(element, Is.EqualTo(refValues[index++]));
+        }
+    }
+    
+    [Test]
+    public void RcCyclicBuffer_EnumeratorWorks()
+    {
+        var refValues = new[] { 4, 3, 2, 1, 0 };
+        var buffer = new RcCyclicBuffer<int>(5, refValues);
+
+        var index = 0;
+        var enumerator = buffer.GetEnumerator();
+        enumerator.Reset();
+        while (enumerator.MoveNext())
+        {
+            Assert.That(enumerator.Current, Is.EqualTo(refValues[index++]));
+        }
+        
+        // Ensure Reset works properly
+        index = 0;
+        enumerator.Reset();
+        while (enumerator.MoveNext())
+        {
+            Assert.That(enumerator.Current, Is.EqualTo(refValues[index++]));
+        }
+    }
 }
\ No newline at end of file