using System;

using System.Text;

using System.IO;



namespace Tools.Common

{

   /// <summary>

   /// Get the CRC-32 Value for a String, Byte array or Stream

   /// </summary>

   public class CRC32

   {

      readonly static uint[] skCRCLookup = new uint[] {

         0x00000000, 0x77073096, 0xEE0E612C, 0x990951BA,

         0x076DC419, 0x706AF48F, 0xE963A535, 0x9E6495A3,

         0x0EDB8832, 0x79DCB8A4, 0xE0D5E91E, 0x97D2D988,

         0x09B64C2B, 0x7EB17CBD, 0xE7B82D07, 0x90BF1D91,

         0x1DB71064, 0x6AB020F2, 0xF3B97148, 0x84BE41DE,

         0x1ADAD47D, 0x6DDDE4EB, 0xF4D4B551, 0x83D385C7,

         0x136C9856, 0x646BA8C0, 0xFD62F97A, 0x8A65C9EC,

         0x14015C4F, 0x63066CD9, 0xFA0F3D63, 0x8D080DF5,

         0x3B6E20C8, 0x4C69105E, 0xD56041E4, 0xA2677172,

         0x3C03E4D1, 0x4B04D447, 0xD20D85FD, 0xA50AB56B,

         0x35B5A8FA, 0x42B2986C, 0xDBBBC9D6, 0xACBCF940,

         0x32D86CE3, 0x45DF5C75, 0xDCD60DCF, 0xABD13D59,

         0x26D930AC, 0x51DE003A, 0xC8D75180, 0xBFD06116,

         0x21B4F4B5, 0x56B3C423, 0xCFBA9599, 0xB8BDA50F,

         0x2802B89E, 0x5F058808, 0xC60CD9B2, 0xB10BE924,

         0x2F6F7C87, 0x58684C11, 0xC1611DAB, 0xB6662D3D,



         0x76DC4190, 0x01DB7106, 0x98D220BC, 0xEFD5102A,

         0x71B18589, 0x06B6B51F, 0x9FBFE4A5, 0xE8B8D433,

         0x7807C9A2, 0x0F00F934, 0x9609A88E, 0xE10E9818,

         0x7F6A0DBB, 0x086D3D2D, 0x91646C97, 0xE6635C01,

         0x6B6B51F4, 0x1C6C6162, 0x856530D8, 0xF262004E,

         0x6C0695ED, 0x1B01A57B, 0x8208F4C1, 0xF50FC457,

         0x65B0D9C6, 0x12B7E950, 0x8BBEB8EA, 0xFCB9887C,

         0x62DD1DDF, 0x15DA2D49, 0x8CD37CF3, 0xFBD44C65,

         0x4DB26158, 0x3AB551CE, 0xA3BC0074, 0xD4BB30E2,

         0x4ADFA541, 0x3DD895D7, 0xA4D1C46D, 0xD3D6F4FB,

         0x4369E96A, 0x346ED9FC, 0xAD678846, 0xDA60B8D0,

         0x44042D73, 0x33031DE5, 0xAA0A4C5F, 0xDD0D7CC9,

         0x5005713C, 0x270241AA, 0xBE0B1010, 0xC90C2086,

         0x5768B525, 0x206F85B3, 0xB966D409, 0xCE61E49F,

         0x5EDEF90E, 0x29D9C998, 0xB0D09822, 0xC7D7A8B4,

         0x59B33D17, 0x2EB40D81, 0xB7BD5C3B, 0xC0BA6CAD,



         0xEDB88320, 0x9ABFB3B6, 0x03B6E20C, 0x74B1D29A,

         0xEAD54739, 0x9DD277AF, 0x04DB2615, 0x73DC1683,

         0xE3630B12, 0x94643B84, 0x0D6D6A3E, 0x7A6A5AA8,

         0xE40ECF0B, 0x9309FF9D, 0x0A00AE27, 0x7D079EB1,

         0xF00F9344, 0x8708A3D2, 0x1E01F268, 0x6906C2FE,

         0xF762575D, 0x806567CB, 0x196C3671, 0x6E6B06E7,

         0xFED41B76, 0x89D32BE0, 0x10DA7A5A, 0x67DD4ACC,

         0xF9B9DF6F, 0x8EBEEFF9, 0x17B7BE43, 0x60B08ED5,

         0xD6D6A3E8, 0xA1D1937E, 0x38D8C2C4, 0x4FDFF252,

         0xD1BB67F1, 0xA6BC5767, 0x3FB506DD, 0x48B2364B,

         0xD80D2BDA, 0xAF0A1B4C, 0x36034AF6, 0x41047A60,

         0xDF60EFC3, 0xA867DF55, 0x316E8EEF, 0x4669BE79,

         0xCB61B38C, 0xBC66831A, 0x256FD2A0, 0x5268E236,

         0xCC0C7795, 0xBB0B4703, 0x220216B9, 0x5505262F,

         0xC5BA3BBE, 0xB2BD0B28, 0x2BB45A92, 0x5CB36A04,

         0xC2D7FFA7, 0xB5D0CF31, 0x2CD99E8B, 0x5BDEAE1D,



         0x9B64C2B0, 0xEC63F226, 0x756AA39C, 0x026D930A,

         0x9C0906A9, 0xEB0E363F, 0x72076785, 0x05005713,

         0x95BF4A82, 0xE2B87A14, 0x7BB12BAE, 0x0CB61B38,

         0x92D28E9B, 0xE5D5BE0D, 0x7CDCEFB7, 0x0BDBDF21,

         0x86D3D2D4, 0xF1D4E242, 0x68DDB3F8, 0x1FDA836E,

         0x81BE16CD, 0xF6B9265B, 0x6FB077E1, 0x18B74777,

         0x88085AE6, 0xFF0F6A70, 0x66063BCA, 0x11010B5C,

         0x8F659EFF, 0xF862AE69, 0x616BFFD3, 0x166CCF45,

         0xA00AE278, 0xD70DD2EE, 0x4E048354, 0x3903B3C2,

         0xA7672661, 0xD06016F7, 0x4969474D, 0x3E6E77DB,

         0xAED16A4A, 0xD9D65ADC, 0x40DF0B66, 0x37D83BF0,

         0xA9BCAE53, 0xDEBB9EC5, 0x47B2CF7F, 0x30B5FFE9,

         0xBDBDF21C, 0xCABAC28A, 0x53B39330, 0x24B4A3A6,

         0xBAD03605, 0xCDD70693, 0x54DE5729, 0x23D967BF,

         0xB3667A2E, 0xC4614AB8, 0x5D681B02, 0x2A6F2B94,

         0xB40BBE37, 0xC30C8EA1, 0x5A05DF1B, 0x2D02EF8D};

      

      //readonly static Encoding encoder = Encoding.GetEncoding(0); // Default codepage, can't use this otherwise CRC's would change for different computers

      readonly static Encoding skEncoder = Encoding.GetEncoding(437);  // Standard US OEM (IBM437 - OEM United States)

      readonly static uint skPoly = 4294967295;



      /// <summary>

      /// Get the crc32 value for an entire Stream, setting the position to zero.

      /// </summary>

      /// <param name="st">The stream to perform the crc32 calculation on.</param>

      /// <returns>The crc32 value.</returns>

      static public uint CalculateCRC(Stream st) 

      {

         return CalculateCRC(st, 0, st.Length); 

      } 



      /// <summary>

      /// Get the crc32 value for a Stream, setting the position to to the beginPosition and calculation to the length.

      /// The position is set back to the original position when complete.

      /// </summary>

      /// <param name="st">The stream to perform the crc32 calculation on.</param>

      /// <param name="beginPosition">The begin position of the stream to start the calculation.</param>

      /// <param name="length">The length you wish to run the calculation on.</param>

      /// <returns>The crc32 value.</returns>

      static public uint CalculateCRC(Stream st, long beginPosition, long length) 

      {

         uint crcVal = skPoly;

         long originalPos = st.Position;

         long endPos = beginPosition + length;

         byte by;



         if (endPos > st.Length) 

         {

            throw new Exception("Out of bounds. beginposition + length is greater than the length of the Stream");

         }



         try

         {

            st.Position = beginPosition;

            BufferedStream bs = new BufferedStream(st);

            

            for(long i = beginPosition; i < endPos; i++) 

            { 

               by =  Convert.ToByte(bs.ReadByte());

               crcVal = (crcVal >> 8) ^ skCRCLookup[(crcVal & 0xFF) ^ by];

            }

         }

         catch (Exception e)

         {

            Console.WriteLine(e.ToString());

         }

         finally

         {

         //For now do nothing

         }

         st.Position = originalPos;

         

         crcVal ^= skPoly;

         return crcVal;

      } 



      /// <summary>

      /// Get the crc32 value for a String.

      /// </summary>

      /// <param name="text">The string you wish to calculate the crc32 value on.</param>

      /// <returns>The CRC-32 value.</returns>

      static public uint CalculateCRC(string text) 

      {

         byte[] buffer; 

         buffer = skEncoder.GetBytes(text);

         return CalculateCRC(buffer); 

      } 



      /// <summary>

      /// Get the CRC-32 value for a byte[].

      /// </summary>

      /// <param name="by">The byte[] you wish to calculate the crc32 value on</param>

      /// <returns>The CRC-32 value.</returns>

      static public uint CalculateCRC(byte[] by) 

      {

         uint crcVal = skPoly;

         long len;

         len = by.Length;

         for(long i = 0; i < len; i++) 

         { 

            crcVal = (crcVal >> 8) ^ skCRCLookup[(crcVal & 0xFF) ^ by[i]];

         }

         crcVal ^= skPoly;

         return crcVal;

      }

   }

}

