diff --git a/StgSharp.RegularAnalysis/Text/CharSetEmitter.cs b/StgSharp.RegularAnalysis/Text/CharSetEmitter.cs
new file mode 100644
index 00000000..f0105bac
--- /dev/null
+++ b/StgSharp.RegularAnalysis/Text/CharSetEmitter.cs
@@ -0,0 +1,115 @@
+//-----------------------------------------------------------------------
+// -----------------------------------------------------------------------
+// file="CharSetEmitter"
+// Project: StgSharp
+// AuthorGroup: Nitload
+// Copyright (c) Nitload. All rights reserved.
+//     
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+//     
+// -----------------------------------------------------------------------
+// -----------------------------------------------------------------------
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace StgSharp.RegularAnalysis.Text
+{
+    internal enum CharSetType
+    {
+
+        None,
+        Single,
+        Range,
+        Set
+
+    }
+
+    internal record struct CharSet(
+                           string value,
+                           CharSetType t,
+                           bool accept
+    )
+    {
+
+        public bool IsAcceptable { get; set; } = accept;
+
+        public CharSetType Type { get; set; } = t;
+
+        public string Value { get; set; } = value;
+
+    }
+
+    internal class CharSetEmitter
+    {
+
+        public static CharSet[] FigureCharSetType(
+                                ReadOnlySpan<char> source
+        )
+        {
+            // range or single
+            bool accept;
+            if (source[0] == '[')
+            {
+                int idx;
+                accept = source[1] != '^';
+                idx = accept ? 1 : 2;
+                ReadOnlySpan<char> seq = source.Slice(idx, source.Length - idx - 1);
+                if (seq.IndexOf('-') == -1)
+                {
+                    return [new CharSet(seq.ToString(), CharSetType.Single, accept)];
+                } else
+                {
+                    List<CharSet> list = [];
+                    for (int i = 0; i < seq.Length && seq.Length > 0; )
+                    {
+                        int pos = seq.IndexOf('-');
+                        if (pos > 1) {
+                            list.Add(new(seq[0..(pos - 1)].ToString(), CharSetType.Single, accept));
+                        }
+                        list.Add(new($"{seq[pos - 1]}{seq[pos + 1]}", CharSetType.Range, accept));
+                        i = pos + 2;
+                        seq = seq[i..];
+                    }
+                    return [.. list];
+                }
+            } else if (source[0] == '\\')
+            {
+                // set
+                accept = char.IsAsciiLetterUpper(source[0]);
+                return char.ToLower(source[0], CultureInfo.InvariantCulture)
+                switch
+                {
+                    's' => [new("s", CharSetType.Set, accept)],
+                    'w' => [new("w", CharSetType.Set, accept)],
+                    'd' => [new("d", CharSetType.Set, accept)],
+                    _ => throw new NotSupportedException()
+                };
+            } else
+            {
+                // unknown, throw
+                throw new InvalidCastException($"Unknown char set: {source}");
+            }
+        }
+
+    }
+}
diff --git a/StgSharp.RegularAnalysis/Text/RegexAnalyzer.IROptimize.cs b/StgSharp.RegularAnalysis/Text/RegexAnalyzer.IROptimize.cs
index 56fb2793..a9a15ada 100644
--- a/StgSharp.RegularAnalysis/Text/RegexAnalyzer.IROptimize.cs
+++ b/StgSharp.RegularAnalysis/Text/RegexAnalyzer.IROptimize.cs
@@ -59,6 +59,7 @@ namespace StgSharp.RegularAnalysis.Text
             {
                 int process_count = 0;
                 int last = int.Min(origin_span.Length, index + 8);
+                opt_win_sp.Clear();
                 origin_span[index..last].CopyTo(opt_win_sp);
 
                 int result;
@@ -140,6 +141,7 @@ namespace StgSharp.RegularAnalysis.Text
             {
                 int process_count = 0;
                 int last = int.Min(origin_span.Length, index + 8);
+                opt_win_sp.Clear();
                 origin_span[index..last].CopyTo(opt_win_sp);
 
                 if (opt_win_sp[0] is IRegexComplex { IsFullyOptimized: true } skip)