Removed bound checks in SharedUrlHelper.IsLocalUrl and use JIT unrolling for checks

src/Shared/ResultsHelpers/SharedUrlHelper.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Runtime.CompilerServices;
 using Microsoft.AspNetCore.Http;
 
 namespace Microsoft.AspNetCore.Internal;
@@ -32,49 +33,50 @@ internal static class SharedUrlHelper
 
     internal static bool IsLocalUrl([NotNullWhen(true)] string? url)
     {
-        if (string.IsNullOrEmpty(url))
+        var urlSpan = url.AsSpan();
+
+        if (urlSpan.IsEmpty)
         {
             return false;
         }
 
         // Allows "/" or "/foo" but not "//" or "/\".
-        if (url[0] == '/')
+        if (urlSpan[0] == '/')
         {
             // url is exactly "/"
-            if (url.Length == 1)
+            if (urlSpan.Length < 2)
             {
                 return true;
             }
 
             // url doesn't start with "//" or "/\"
-            if (url[1] != '/' && url[1] != '\\')
+            if (urlSpan[1] is not '/' and '\\')
             {
-                return !HasControlCharacter(url.AsSpan(1));
+                return !HasControlCharacter(urlSpan.Slice(1));
             }
 
             return false;
         }
 
         // Allows "~/" or "~/foo" but not "~//" or "~/\".
-        if (url[0] == '~' && url.Length > 1 && url[1] == '/')
+        if (urlSpan.StartsWith("~/"))
         {
             // url is exactly "~/"
-            if (url.Length == 2)
+            if (urlSpan.Length < 3)
             {
                 return true;
             }
 
             // url doesn't start with "~//" or "~/\"
-            if (url[2] != '/' && url[2] != '\\')
+            if (urlSpan[2] is not '/' and '\\')
             {
-                return !HasControlCharacter(url.AsSpan(2));
+                return !HasControlCharacter(urlSpan.Slice(2));
             }
-
-            return false;
         }
 
         return false;
 
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         static bool HasControlCharacter(ReadOnlySpan<char> readOnlySpan)
         {
             // URLs may not contain ASCII control characters.