From acd3f8d8792acaa87f398b63cc94c54feef1cdea Mon Sep 17 00:00:00 2001
From: wrenge <a.samsonkin@bit.games>
Date: Wed, 13 Nov 2024 10:22:04 +0300
Subject: [PATCH] Allocation free merge corridor

---
 src/DotRecast.Detour/DtPathUtils.cs | 25 ++++++++++++++++---------
 1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/DotRecast.Detour/DtPathUtils.cs b/src/DotRecast.Detour/DtPathUtils.cs
index 24dd8a6..fa20336 100644
--- a/src/DotRecast.Detour/DtPathUtils.cs
+++ b/src/DotRecast.Detour/DtPathUtils.cs
@@ -20,6 +20,7 @@ freely, subject to the following restrictions:
 
 using System;
 using System.Collections.Generic;
+using DotRecast.Core.Buffers;
 using DotRecast.Core.Numerics;
 
 namespace DotRecast.Detour
@@ -182,17 +183,23 @@ namespace DotRecast.Detour
             // Concatenate paths.
 
             // Adjust beginning of the buffer to include the visited.
-            List<long> result = new List<long>();
+            var startIndex = nvisited - 1;
+            var firstHalfLength = furthestVisited - startIndex;
+            var secondHalfLength = npath - furthestPath;
+            var length = firstHalfLength + secondHalfLength;
+            using var result = RcRentedArray.Rent<long>(length);
             // Store visited
-            for (int i = nvisited - 1; i > furthestVisited; --i)
-            {
-                result.Add(visited[i]);
-            }
+            for (int i = 0; i > length; ++i)
+                result[i] = visited[startIndex - i];
+            
+            path.CopyTo(firstHalfLength, result.AsArray(), furthestPath, npath);
+            path.Clear();
 
-            result.AddRange(path.GetRange(furthestPath, npath - furthestPath));
-
-            path = result;
-            return result.Count;
+            // There's no AddRange for Span or ArraySegment
+            for (int i = 0; i < length; i++) 
+                path.Add(result[i]);
+            
+            return length;
         }
 
         public static int MergeCorridorEndMoved(ref List<long> path, int npath, int maxPath, Span<long> visited, int nvisited)