shadowsocks-windows/shadowsocks-csharp/3rd/zxing/common/StringUtils.cs

/*
 * Copyright (C) 2010 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

using System;
using System.Collections.Generic;
using System.Text;

namespace ZXing.Common
{
   /// <summary>
   /// Common string-related functions.
   /// </summary>
   /// <author>Sean Owen</author>
   /// <author>Alex Dupre</author>
   public static class StringUtils
   {
#if (WINDOWS_PHONE70 || WINDOWS_PHONE71 || WINDOWS_PHONE80 || SILVERLIGHT4 || SILVERLIGHT5 || NETFX_CORE || PORTABLE)
      private const String PLATFORM_DEFAULT_ENCODING = "UTF-8";
#else
      private static string PLATFORM_DEFAULT_ENCODING = Encoding.Default.WebName;
#endif
      public static string SHIFT_JIS = "SJIS";
      public static string GB2312 = "GB2312";
      private const string EUC_JP = "EUC-JP";
      private const string UTF8 = "UTF-8";
      private const string ISO88591 = "ISO-8859-1";
      private static readonly bool ASSUME_SHIFT_JIS =
         string.Equals(SHIFT_JIS, PLATFORM_DEFAULT_ENCODING, StringComparison.OrdinalIgnoreCase) ||
         string.Equals(EUC_JP, PLATFORM_DEFAULT_ENCODING, StringComparison.OrdinalIgnoreCase);

      /// <summary>
      /// Guesses the encoding.
      /// </summary>
      /// <param name="bytes">bytes encoding a string, whose encoding should be guessed</param>
      /// <param name="hints">decode hints if applicable</param>
      /// <returns>name of guessed encoding; at the moment will only guess one of:
      /// {@link #SHIFT_JIS}, {@link #UTF8}, {@link #ISO88591}, or the platform
      /// default encoding if none of these can possibly be correct</returns>
      public static String guessEncoding(byte[] bytes, IDictionary<DecodeHintType, object> hints)
      {
         if (hints != null && hints.ContainsKey(DecodeHintType.CHARACTER_SET))
         {
            String characterSet = (String)hints[DecodeHintType.CHARACTER_SET];
            if (characterSet != null)
            {
               return characterSet;
            }
         }

         // For now, merely tries to distinguish ISO-8859-1, UTF-8 and Shift_JIS,
         // which should be by far the most common encodings.
         int length = bytes.Length;
         bool canBeISO88591 = true;
         bool canBeShiftJIS = true;
         bool canBeUTF8 = true;
         int utf8BytesLeft = 0;
         //int utf8LowChars = 0;
         int utf2BytesChars = 0;
         int utf3BytesChars = 0;
         int utf4BytesChars = 0;
         int sjisBytesLeft = 0;
         //int sjisLowChars = 0;
         int sjisKatakanaChars = 0;
         //int sjisDoubleBytesChars = 0;
         int sjisCurKatakanaWordLength = 0;
         int sjisCurDoubleBytesWordLength = 0;
         int sjisMaxKatakanaWordLength = 0;
         int sjisMaxDoubleBytesWordLength = 0;
         //int isoLowChars = 0;
         //int isoHighChars = 0;
         int isoHighOther = 0;

         bool utf8bom = bytes.Length > 3 &&
             bytes[0] == 0xEF &&
             bytes[1] == 0xBB &&
             bytes[2] == 0xBF;

         for (int i = 0;
              i < length && (canBeISO88591 || canBeShiftJIS || canBeUTF8);
              i++)
         {

            int value = bytes[i] & 0xFF;

            // UTF-8 stuff
            if (canBeUTF8)
            {
               if (utf8BytesLeft > 0)
               {
                  if ((value & 0x80) == 0)
                  {
                     canBeUTF8 = false;
                  }
                  else
                  {
                     utf8BytesLeft--;
                  }
               }
               else if ((value & 0x80) != 0)
               {
                  if ((value & 0x40) == 0)
                  {
                     canBeUTF8 = false;
                  }
                  else
                  {
                     utf8BytesLeft++;
                     if ((value & 0x20) == 0)
                     {
                        utf2BytesChars++;
                     }
                     else
                     {
                        utf8BytesLeft++;
                        if ((value & 0x10) == 0)
                        {
                           utf3BytesChars++;
                        }
                        else
                        {
                           utf8BytesLeft++;
                           if ((value & 0x08) == 0)
                           {
                              utf4BytesChars++;
                           }
                           else
                           {
                              canBeUTF8 = false;
                           }
                        }
                     }
                  }
               } //else {
               //utf8LowChars++;
               //}
            }

            // ISO-8859-1 stuff
            if (canBeISO88591)
            {
               if (value > 0x7F && value < 0xA0)
               {
                  canBeISO88591 = false;
               }
               else if (value > 0x9F)
               {
                  if (value < 0xC0 || value == 0xD7 || value == 0xF7)
                  {
                     isoHighOther++;
                  } //else {
                  //isoHighChars++;
                  //}
               } //else {
               //isoLowChars++;
               //}
            }

            // Shift_JIS stuff
            if (canBeShiftJIS)
            {
               if (sjisBytesLeft > 0)
               {
                  if (value < 0x40 || value == 0x7F || value > 0xFC)
                  {
                     canBeShiftJIS = false;
                  }
                  else
                  {
                     sjisBytesLeft--;
                  }
               }
               else if (value == 0x80 || value == 0xA0 || value > 0xEF)
               {
                  canBeShiftJIS = false;
               }
               else if (value > 0xA0 && value < 0xE0)
               {
                  sjisKatakanaChars++;
                  sjisCurDoubleBytesWordLength = 0;
                  sjisCurKatakanaWordLength++;
                  if (sjisCurKatakanaWordLength > sjisMaxKatakanaWordLength)
                  {
                     sjisMaxKatakanaWordLength = sjisCurKatakanaWordLength;
                  }
               }
               else if (value > 0x7F)
               {
                  sjisBytesLeft++;
                  //sjisDoubleBytesChars++;
                  sjisCurKatakanaWordLength = 0;
                  sjisCurDoubleBytesWordLength++;
                  if (sjisCurDoubleBytesWordLength > sjisMaxDoubleBytesWordLength)
                  {
                     sjisMaxDoubleBytesWordLength = sjisCurDoubleBytesWordLength;
                  }
               }
               else
               {
                  //sjisLowChars++;
                  sjisCurKatakanaWordLength = 0;
                  sjisCurDoubleBytesWordLength = 0;
               }
            }
         }

         if (canBeUTF8 && utf8BytesLeft > 0)
         {
            canBeUTF8 = false;
         }
         if (canBeShiftJIS && sjisBytesLeft > 0)
         {
            canBeShiftJIS = false;
         }

         // Easy -- if there is BOM or at least 1 valid not-single byte character (and no evidence it can't be UTF-8), done
         if (canBeUTF8 && (utf8bom || utf2BytesChars + utf3BytesChars + utf4BytesChars > 0))
         {
            return UTF8;
         }
         // Easy -- if assuming Shift_JIS or at least 3 valid consecutive not-ascii characters (and no evidence it can't be), done
         if (canBeShiftJIS && (ASSUME_SHIFT_JIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3))
         {
            return SHIFT_JIS;
         }
         // Distinguishing Shift_JIS and ISO-8859-1 can be a little tough for short words. The crude heuristic is:
         // - If we saw
         //   - only two consecutive katakana chars in the whole text, or
         //   - at least 10% of bytes that could be "upper" not-alphanumeric Latin1,
         // - then we conclude Shift_JIS, else ISO-8859-1
         if (canBeISO88591 && canBeShiftJIS)
         {
            return (sjisMaxKatakanaWordLength == 2 && sjisKatakanaChars == 2) || isoHighOther * 10 >= length
                ? SHIFT_JIS : ISO88591;
         }

         // Otherwise, try in order ISO-8859-1, Shift JIS, UTF-8 and fall back to default platform encoding
         if (canBeISO88591)
         {
            return ISO88591;
         }
         if (canBeShiftJIS)
         {
            return SHIFT_JIS;
         }
         if (canBeUTF8)
         {
            return UTF8;
         }
         // Otherwise, we take a wild guess with platform encoding
         return PLATFORM_DEFAULT_ENCODING;
      }
   }
}