[Core] FilePath no longer creates extra strings on IsChildPathof.

Rewrote the algorithm so it creates fewer strings. The only do the check when we get a match on the first path, so it shouldn't slow down the code a lot.

On 10,000,000 iterations, the benchmark results are as given:

New with slash: 1331ms
Old with slash: 1311ms

New without slash: 1397ms
Old without slash: 3088ms

This fixes memory pressure, slightly makes the slash variant slower, but
greatly improved the variant without slash.

1 files changed, 9 insertions, 5 deletions

diff --git a/main/src/core/MonoDevelop.Core/MonoDevelop.Core/FilePath.cs b/main/src/core/MonoDevelop.Core/MonoDevelop.Core/FilePath.cs
index 0f8f88efd2..f5a55cf727 100644
--- a/main/src/core/MonoDevelop.Core/MonoDevelop.Core/FilePath.cs
+++ b/main/src/core/MonoDevelop.Core/MonoDevelop.Core/FilePath.cs
@@ -172,11 +172,15 @@ namespace MonoDevelop.Core
 		}

 

 		public bool IsChildPathOf (FilePath basePath)

-		{

-			if (basePath.fileName [basePath.fileName.Length - 1] != Path.DirectorySeparatorChar)

-				return fileName.StartsWith (basePath.fileName + Path.DirectorySeparatorChar, PathComparison);
-			else

-				return fileName.StartsWith (basePath.fileName, PathComparison);
+		{
+			bool startsWith = fileName.StartsWith (basePath.fileName, PathComparison);
+			if (startsWith && basePath.fileName [basePath.fileName.Length - 1] != Path.DirectorySeparatorChar) {

+				// If the last character isn't a path separator character, check whether the string we're searching in

+				// has more characters than the string we're looking for then check the character.
+				if (fileName.Length > basePath.fileName.Length)
+					startsWith &= fileName [basePath.fileName.Length] == Path.DirectorySeparatorChar;
+			}
+			return startsWith;

 		}

 

 		public FilePath ChangeExtension (string ext)