[ElementAt] improve ElementAt

reegeek · reegeek · commit 30d28ad738fe · 2020-10-31T09:24:31.000+01:00
diff --git a/Documents/BenchmarksResults/ElementAtOnArray.md b/Documents/BenchmarksResults/ElementAtOnArray.md
@@ -7,16 +7,17 @@
 ``` ini
 
 BenchmarkDotNet=v0.12.0, OS=Windows 10.0.19041
-Intel Core i7-7700 CPU 3.60GHz (Kaby Lake), 1 CPU, 8 logical and 4 physical cores
-.NET Core SDK=3.1.403
+Intel Core i7-8750H CPU 2.20GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
+.NET Core SDK=5.0.100-preview.7.20366.6
   [Host]     : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
   DefaultJob : .NET Core 3.1.9 (CoreCLR 4.700.20.47201, CoreFX 4.700.20.47203), X64 RyuJIT
 
 
 ```
-|              Method |      Mean |     Error |    StdDev | Ratio |  Gen 0 | Gen 1 | Gen 2 | Allocated |
-|-------------------- |----------:|----------:|----------:|------:|-------:|------:|------:|----------:|
-|                Linq | 26.625 ns | 0.2574 ns | 0.2408 ns |  1.00 |      - |     - |     - |         - |
-|      EnumerableLinq | 26.390 ns | 0.4745 ns | 0.3962 ns |  0.99 |      - |     - |     - |         - |
-|          StructLinq | 13.418 ns | 0.2688 ns | 0.2761 ns |  0.51 | 0.0076 |     - |     - |      32 B |
-| StructLinqZeroAlloc |  4.414 ns | 0.0438 ns | 0.0366 ns |  0.17 |      - |     - |     - |         - |
+|                            Method |       Mean |     Error |    StdDev | Ratio | RatioSD |  Gen 0 | Gen 1 | Gen 2 | Allocated |
+|---------------------------------- |-----------:|----------:|----------:|------:|--------:|-------:|------:|------:|----------:|
+|                              Linq |  24.122 ns | 0.3471 ns | 0.3077 ns |  1.00 |    0.00 |      - |     - |     - |         - |
+|                    EnumerableLinq |  24.105 ns | 0.2221 ns | 0.2077 ns |  1.00 |    0.01 |      - |     - |     - |         - |
+|                        StructLinq |  12.324 ns | 0.2485 ns | 0.2203 ns |  0.51 |    0.01 | 0.0068 |     - |     - |      32 B |
+|               StructLinqZeroAlloc |   4.066 ns | 0.0562 ns | 0.0525 ns |  0.17 |    0.00 |      - |     - |     - |         - |
+| StructLinqZeroAllocWithEnumerator | 700.381 ns | 2.7479 ns | 2.5704 ns | 29.04 |    0.42 |      - |     - |     - |         - |
diff --git a/src/StructLinq.Benchmark/ElementAtOnArray.cs b/src/StructLinq.Benchmark/ElementAtOnArray.cs
@@ -1,6 +1,7 @@
 ﻿using System.Collections.Generic;
 using System.Linq;
 using BenchmarkDotNet.Attributes;
+using StructLinq.Array;
 
 namespace StructLinq.Benchmark
 {
@@ -29,5 +30,9 @@ public ElementAtOnArray()
         [Benchmark]
         public int StructLinqZeroAlloc() => array.ToStructEnumerable().ElementAt(Count / 2, x=>x);
 
+        [Benchmark]
+        public int StructLinqZeroAllocWithEnumerator() => array.ToStructEnumerable().ElementAt(Count / 2, x => (IStructEnumerable<int, ArrayStructEnumerator<int>>)x);
+
+
     }
 }
diff --git a/src/StructLinq/ElementAt/RefStructEnumerable.ElementAt.cs b/src/StructLinq/ElementAt/RefStructEnumerable.ElementAt.cs
@@ -15,35 +15,45 @@ private static bool RefTryInnerElementAt<T, TEnumerator>(ref TEnumerator enumera
             if (index < 0)
                 return false;
 
-            int i = 0;
-            while (enumerator.MoveNext()&& i<=index)
+            while (true)
             {
-                ref var current = ref enumerator.Current;
-                elementAt = current;
-                i++;
+                if (!enumerator.MoveNext())
+                {
+                    enumerator.Dispose();
+                    return false;
+                }
+                if (index == 0)
+                {
+                    elementAt = ref enumerator.Current;
+                    enumerator.Dispose();
+                    return true;
+                }
+                index--;
             }
-            enumerator.Dispose();
-            return i == index + 1;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         private static T RefInnerElementAt<T, TEnumerator>(ref TEnumerator enumerator, int index)
             where TEnumerator : struct, IRefStructEnumerator<T>
         {
+
             if (index < 0)
                 throw new ArgumentOutOfRangeException("index");
-            int i = 0;
-            T result = default;
-            while (enumerator.MoveNext()&& i<=index)
+            while (true)
             {
-                ref var current = ref enumerator.Current;
-                result = current;
-                i++;
+                if (!enumerator.MoveNext())
+                {
+                    enumerator.Dispose();
+                    throw new ArgumentOutOfRangeException("index");
+                }
+                if (index == 0)
+                {
+                    ref var innerElementAt = ref enumerator.Current;
+                    enumerator.Dispose();
+                    return innerElementAt;
+                }
+                index--;
             }
-            enumerator.Dispose();
-            if (i == index + 1)
-                return result;
-            throw new ArgumentOutOfRangeException("index");
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
diff --git a/src/StructLinq/ElementAt/StructEnumerable.ElementAt.cs b/src/StructLinq/ElementAt/StructEnumerable.ElementAt.cs
@@ -14,15 +14,22 @@ private static bool TryInnerElementAt<T, TEnumerator>(ref TEnumerator enumerator
         {
             if (index < 0)
                 return false;
-            int i = 0;
-            while (enumerator.MoveNext()&& i<=index)
+
+            while (true)
             {
-                var current = enumerator.Current;
-                elementAt = current;
-                i++;
+                if (!enumerator.MoveNext())
+                {
+                    enumerator.Dispose();
+                    return false;
+                }
+                if (index == 0)
+                {
+                    elementAt = enumerator.Current;
+                    enumerator.Dispose();
+                    return true;
+                }
+                index--;
             }
-            enumerator.Dispose();
-            return i == index + 1;
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -31,18 +38,21 @@ private static T InnerElementAt<T, TEnumerator>(ref TEnumerator enumerator, int
         {
             if (index < 0)
                 throw new ArgumentOutOfRangeException("index");
-            int i = 0;
-            T result = default;
-            while (enumerator.MoveNext()&& i<=index)
+            while (true)
             {
-                var current = enumerator.Current;
-                result = current;
-                i++;
+                if (!enumerator.MoveNext())
+                {
+                    enumerator.Dispose();
+                    throw new ArgumentOutOfRangeException("index");
+                }
+                if (index == 0)
+                {
+                    var innerElementAt = enumerator.Current;
+                    enumerator.Dispose();
+                    return innerElementAt;
+                }
+                index--;
             }
-            enumerator.Dispose();
-            if (i == index+1)
-                return result;
-            throw new ArgumentOutOfRangeException("index");
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]

Original file line number	Diff line number	Diff line change
`@@ -1,6 +1,7 @@`
`1`	`1`	`using System.Collections.Generic;`
`2`	`2`	`using System.Linq;`
`3`	`3`	`using BenchmarkDotNet.Attributes;`
	`4`	`+using StructLinq.Array;`
`4`	`5`
`5`	`6`	`namespace StructLinq.Benchmark`
`6`	`7`	`{`
`@@ -29,5 +30,9 @@ public ElementAtOnArray()`
`29`	`30`	`[Benchmark]`
`30`	`31`	`public int StructLinqZeroAlloc() => array.ToStructEnumerable().ElementAt(Count / 2, x=>x);`
`31`	`32`
	`33`	`+ [Benchmark]`
	`34`	`+ public int StructLinqZeroAllocWithEnumerator() => array.ToStructEnumerable().ElementAt(Count / 2, x => (IStructEnumerable<int, ArrayStructEnumerator<int>>)x);`
	`35`	`+`
	`36`	`+`
`32`	`37`	`}`
`33`	`38`	`}`