Refactored Grow method

Author: linkdotnet

CHANGELOG.md

@@ -8,7 +8,7 @@ All notable changes to **ValueStringBuilder** will be documented in this file. T
 
 ### Changed
 - `Dispose` resets the `ValueStringBuilder` to the initial state, so it doesn't lead to undefined behavior when used again
-
+- Use different approach for `Grow` to be a bit more performant
 ## [1.18.5] - 2023-10-19
 
 ### Changed

src/LinkDotNet.StringBuilder/ValueStringBuilder.cs

@@ -313,7 +313,18 @@ private void Grow(int capacity = 0)
         }
 
         var rented = ArrayPool<char>.Shared.Rent(size);
-        buffer[..bufferPosition].CopyTo(rented);
+
+        if (bufferPosition > 0)
+        {
+            ref var sourceRef = ref MemoryMarshal.GetReference(buffer);
+            ref var destinationRef = ref MemoryMarshal.GetReference(rented.AsSpan());
+
+            Unsafe.CopyBlock(
+                ref Unsafe.As<char, byte>(ref destinationRef),
+                ref Unsafe.As<char, byte>(ref sourceRef),
+                (uint)(bufferPosition * sizeof(char)));
+        }
+
         var oldBufferFromPool = arrayFromPool;
         buffer = arrayFromPool = rented;
 

tests/LinkDotNet.StringBuilder.Benchmarks/AppendBenchmark.cs

@@ -5,17 +5,6 @@ namespace LinkDotNet.StringBuilder.Benchmarks;
 [MemoryDiagnoser]
 public class AppendBenchmarks
 {
-    [Benchmark(Baseline = true)]
-    public string DotNetStringBuilder()
-    {
-        var builder = new System.Text.StringBuilder();
-        builder.AppendLine("That is the first line of our benchmark.");
-        builder.AppendLine("We can multiple stuff in here if want.");
-        builder.AppendLine("The idea is that we can resize the internal structure from time to time.");
-        builder.AppendLine("We can also add other Append method if we want. But we keep it easy for now.");
-        return builder.ToString();
-    }
-
     [Benchmark]
     public string ValueStringBuilder()
     {
@@ -27,16 +16,4 @@ public string ValueStringBuilder()
         builder.AppendLine("We can also add other Append method if we want. But we keep it easy for now.");
         return builder.ToString();
     }
-
-    [Benchmark]
-    public string ValueStringBuilderPreAllocated()
-    {
-        using var builder = new ValueStringBuilder(stackalloc char[256]);
-        builder.AppendLine("That is the first line of our benchmark.");
-        builder.AppendLine("We can multiple stuff in here if want.");
-        builder.AppendLine("We can multiple stuff in here if want.");
-        builder.AppendLine("The idea is that we can resize the internal structure from time to time.");
-        builder.AppendLine("We can also add other Append method if we want. But we keep it easy for now.");
-        return builder.ToString();
-    }
 }