update encoding detection

Emby.Common.Implementations/TextEncoding/UniversalDetector/Core/UTF8Prober.cs

@@ -0,0 +1,112 @@
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is Mozilla Universal charset detector code.
+ *
+ * The Initial Developer of the Original Code is
+ * Netscape Communications Corporation.
+ * Portions created by the Initial Developer are Copyright (C) 2001
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *          Shy Shalom <shooshX@gmail.com>
+ *          Rudi Pettazzi <rudi.pettazzi@gmail.com> (C# port)
+ * 
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+namespace UniversalDetector.Core
+{
+    public class UTF8Prober : CharsetProber
+    {
+        private static float ONE_CHAR_PROB = 0.50f;
+        private CodingStateMachine codingSM;
+        private int numOfMBChar;
+
+        public UTF8Prober()
+        {
+            numOfMBChar = 0; 
+            codingSM = new CodingStateMachine(new UTF8SMModel());
+            Reset();
+        }
+        
+        public override string GetCharsetName() {
+            return "UTF-8";
+        }
+
+        public override void Reset()
+        {
+            codingSM.Reset();
+            numOfMBChar = 0;
+            state = ProbingState.Detecting;
+        }
+
+        public override ProbingState HandleData(byte[] buf, int offset, int len)
+        {
+            int codingState = SMModel.START;
+            int max = offset + len;
+            
+            for (int i = offset; i < max; i++) {
+
+                codingState = codingSM.NextState(buf[i]);
+
+                if (codingState == SMModel.ERROR) {
+                    state = ProbingState.NotMe;
+                    break;
+                }
+
+                if (codingState == SMModel.ITSME) {
+                    state = ProbingState.FoundIt;
+                    break;
+                }
+
+                if (codingState == SMModel.START) {
+                    if (codingSM.CurrentCharLen >= 2)
+                        numOfMBChar++;
+                }
+            }
+
+            if (state == ProbingState.Detecting)
+                if (GetConfidence() > SHORTCUT_THRESHOLD)
+                    state = ProbingState.FoundIt;
+            return state;
+        }
+
+        public override float GetConfidence()
+        {
+            float unlike = 0.99f;
+            float confidence = 0.0f;
+            
+            if (numOfMBChar < 6) {
+                for (int i = 0; i < numOfMBChar; i++)
+                    unlike *= ONE_CHAR_PROB;
+                confidence = 1.0f - unlike;
+            } else {
+                confidence = 0.99f;
+            }
+            return confidence;
+
+        }
+    }
+}