Minor optimizations, improve XML docs and annotations

src/ImageSharp/Memory/MemoryOwnerExtensions.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Buffers;
+using System.Diagnostics.Contracts;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -13,12 +14,29 @@ namespace SixLabors.ImageSharp.Memory
     /// </summary>
     internal static class MemoryOwnerExtensions
     {
+        /// <summary>
+        /// Gets a <see cref="Span{T}"/> from an <see cref="IMemoryOwner{T}"/> instance.
+        /// </summary>
+        /// <param name="buffer">The buffer</param>
+        /// <returns>The <see cref="Span{T}"/></returns>
+        [Pure]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static Span<T> GetSpan<T>(this IMemoryOwner<T> buffer)
-            => buffer.Memory.Span;
+        {
+            return buffer.Memory.Span;
+        }
 
+        /// <summary>
+        /// Gets the length of an <see cref="IMemoryOwner{T}"/> internal buffer.
+        /// </summary>
+        /// <param name="buffer">The buffer</param>
+        /// <returns>The length of the buffer</returns>
+        [Pure]
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static int Length<T>(this IMemoryOwner<T> buffer)
-            => buffer.GetSpan().Length;
+        {
+            return buffer.Memory.Length;
+        }
 
         /// <summary>
         /// Gets a <see cref="Span{T}"/> to an offsetted position inside the buffer.
@@ -26,6 +44,7 @@ namespace SixLabors.ImageSharp.Memory
         /// <param name="buffer">The buffer</param>
         /// <param name="start">The start</param>
         /// <returns>The <see cref="Span{T}"/></returns>
+        [Pure]
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static Span<T> Slice<T>(this IMemoryOwner<T> buffer, int start)
         {
@@ -39,6 +58,7 @@ namespace SixLabors.ImageSharp.Memory
         /// <param name="start">The start</param>
         /// <param name="length">The length of the slice</param>
         /// <returns>The <see cref="Span{T}"/></returns>
+        [Pure]
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static Span<T> Slice<T>(this IMemoryOwner<T> buffer, int start, int length)
         {
@@ -55,8 +75,17 @@ namespace SixLabors.ImageSharp.Memory
             buffer.GetSpan().Clear();
         }
 
+        /// <summary>
+        /// Gets a reference to the first item in the internal buffer for an <see cref="IMemoryOwner{T}"/> instance.
+        /// </summary>
+        /// <param name="buffer">The buffer</param>
+        /// <returns>A reference to the first item within the memory wrapped by <paramref name="buffer"/></returns>
+        [Pure]
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static ref T GetReference<T>(this IMemoryOwner<T> buffer)
-            where T : struct =>
-            ref MemoryMarshal.GetReference(buffer.GetSpan());
+            where T : struct
+        {
+            return ref MemoryMarshal.GetReference(buffer.GetSpan());
+        }
     }
 }