Replace performance tuning

Author: linkdotnet

CHANGELOG.md

@@ -10,6 +10,10 @@ All notable changes to **ValueStringBuilder** will be documented in this file. T
 
 -  implicit cast operator from `string` and `ReadOnlySpan<char>` to the `ValueStringBuilder` with pre-initialized buffer
 
+### Changed
+
+- various path optimizations for replace logic to use less allocations while being faster
+
 ### Removed
 
 - Removed value type overloads for `Append` and `Insert` and just offer `Append(ISpanFormattable)` and `Insert(ISpanFormattable)`, which covers more cases.

src/LinkDotNet.StringBuilder/ValueStringBuilder.Replace.cs

@@ -135,8 +135,29 @@ public void Replace(scoped ReadOnlySpan<char> oldValue, scoped ReadOnlySpan<char
         for (var i = 0; i < hits.Length; i++)
         {
             var index = startIndex + hits[i] + (delta * i);
-            Remove(index, oldValue.Length);
-            Insert(index, newValue);
+
+            // newValue is smaller than old value
+            // We can insert the slice and remove the overhead
+            if (delta < 0)
+            {
+                newValue.CopyTo(buffer[index..]);
+                Remove(index + 1, -delta);
+            }
+
+            // Same length -> We can just replace the memory slice
+            else if (delta == 0)
+            {
+                newValue.CopyTo(buffer[index..]);
+            }
+
+            // newValue is larger than the old value
+            // First add until the old memory region
+            // and insert afterwards the rest
+            else
+            {
+                newValue[..oldValue.Length].CopyTo(buffer[index..]);
+                Insert(index + oldValue.Length, newValue[oldValue.Length..]);
+            }
         }
     }
 }