Substring appears to allocate faster than actually allocating, conver…

…ting some operations to substring accordingly
kevin-montrose · Feb 26, 2012 · c4af501 · c4af501
1 parent 965f3cd
commit c4af501
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Showing 3 changed files with 20 additions and 1 deletion.
diff --git a/FluentStringParser/Directives.cs b/FluentStringParser/Directives.cs
@@ -216,6 +216,7 @@ internal override void Emit(ILGenerator il)
             il.MarkLabel(finished);
         }
 
+        [ExcludeFromCodeCoverage]
         internal override Action<string, T> GetOnFailure()
         {
             return (s, o) => { };

diff --git a/FluentStringParser/ILHelpers.cs b/FluentStringParser/ILHelpers.cs
@@ -550,7 +550,15 @@ internal static void NewParseImpl(ILGenerator il, Type memberType, string format
 
             if (memberType == typeof(string))
             {
-                il.Emit(OpCodes.Newobj, strConst);  // string *built
+                var substring = typeof(string).GetMethod("Substring", new[]{typeof(int), typeof(int)});
+
+                il.StoreScratchInt();               // start char[] *built
+                il.StoreScratchInt2();              // char[] *built
+                il.Emit(OpCodes.Pop);               // *built
+                il.Emit(OpCodes.Ldarg_0);           // string *built
+                il.LoadScratchInt2();               // start string *built
+                il.LoadScratchInt();                // length start string *built
+                il.Emit(OpCodes.Call, substring);   // string *built
 
                 return;
             }

diff --git a/FluentStringParserTests/Tests.cs b/FluentStringParserTests/Tests.cs
@@ -435,6 +435,11 @@ public void HaProxyLogs()
         [TestMethod]
         public void SpeedComparison()
         {
+            // THIS TEST IS EXPECTED TO FAIL
+            //   String performance in the hand written case is *very good*, if you
+            //   can gin up better code for this case in the FSP, submit a patch.
+            //   It's an interesting project.
+
             string[] lines;
             using (var input = new StreamReader(Assembly.GetExecutingAssembly().GetManifestResourceStream("FluentStringParserTests.TestData.txt")))
             {
@@ -1098,6 +1103,11 @@ class StringPerfObject
         [TestMethod]
         public void SimpleStringPerf()
         {
+            // THIS TEST IS EXPECTED TO FAIL
+            //   String performance in the hand written case is *very good*, if you
+            //   can gin up better code for this case in the FSP, submit a patch.
+            //   It's an interesting project.
+
             var regex = new Regex(@"([^,]*?),([^,]*?),([^,]*?),([^,]*)", RegexOptions.Compiled);
             var parserTask =
                 FSBuilder