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CRC32 einer Datei

C# - el_MKay Oktober 15, 2006
3 Ratings 4/5

Sprache: C#

Mit dieser Klasse kann die CRC32 einer Datei erechnet werden.
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;

namespace CRC32
{
    class File_CRC32
    {
        long[] pTable = new long[256];

        //Für Standard CRC32:
        //(Wert kann verändert werden)
        long Poly = 0xEDB88320;

        public File_CRC32()
        {
            long CRC;
            int i, j;

            for (i = 0; i < 256; i++)
            {
                CRC = i;

                for (j = 0; j < 8; j++)
                {
                    if ((CRC & 0x1)==1) {
                        CRC = (CRC >> 1) ^ Poly;
                    } else {
                        CRC = (CRC >> 1);
                    }
                }
                pTable[i] = CRC;
            }

        }

        public uint GetCRC32(string FileName)
        {
            long StreamLength, CRC;
            int BufferSize;
            byte[] Buffer;

            //4KB Buffer
            BufferSize = 0x1000;

            FileStream fs = new FileStream(FileName, FileMode.Open);
            StreamLength = fs.Length;

            CRC = 0xFFFFFFFF;
            while (StreamLength > 0)
            {
                if (StreamLength < BufferSize)
                {
                    BufferSize = (int) StreamLength;
                }
                Buffer = new byte[BufferSize];

                fs.Read(Buffer, 0, BufferSize);

                for (int i=0; i<BufferSize; i++) {
                    CRC = ((CRC & 0xFFFFFF00) / 0x100) & 0xFFFFFF ^ pTable[Buffer[i] ^ CRC & 0xFF];
                }

                StreamLength = StreamLength - BufferSize;
    
            }

            fs.Close();
            CRC = (-(CRC)) - 1; // !(CRC)

            return (uint)CRC;
        }

    }
}

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

namespace CRC32
{
    class File_CRC32
    {
        long[] pTable = new long[256];

        //Für Standard CRC32:
        //(Wert kann verändert werden)
        long Poly = 0xEDB88320;

        public File_CRC32()
        {
            long CRC;
            int i, j;

            for (i = 0; i < 256; i++)
            {
                CRC = i;

                for (j = 0; j < 8; j++)
                {
                    if ((CRC & 0x1)==1) {
                        CRC = (CRC >> 1) ^ Poly;
                    } else {
                        CRC = (CRC >> 1);
                    }
                }
                pTable[i] = CRC;
            }

        }

        public uint GetCRC32(string FileName)
        {
            long StreamLength, CRC;
            int BufferSize;
            byte[] Buffer;

            //4KB Buffer
            BufferSize = 0x1000;

            FileStream fs = new FileStream(FileName, FileMode.Open);
            StreamLength = fs.Length;

            CRC = 0xFFFFFFFF;
            while (StreamLength > 0)
            {
                if (StreamLength < BufferSize)
                {
                    BufferSize = (int) StreamLength;
                }
                Buffer = new byte[BufferSize];

                fs.Read(Buffer, 0, BufferSize);

                for (int i=0; i<BufferSize; i++) {
                    CRC = ((CRC & 0xFFFFFF00) / 0x100) & 0xFFFFFF ^ pTable[Buffer[i] ^ CRC & 0xFF];
                }

                StreamLength = StreamLength - BufferSize;
    
            }

            fs.Close();
            CRC = (-(CRC)) - 1; // !(CRC)

            return (uint)CRC;
        }

    }
}
Abgelegt unter Checksum Checksumme CRC CRC32

Alte URL: /snippet/crc32-einer-datei/238

1 Kommentar

  1. GetCRC32 wirft unter neueren Betriebsystemen öfters mal eine UnauthorizedAccessException. Besser wäre hier, da man sowieso nur lesend auf die Dateien zugreift, eine FileStream-Überladung zu verwenden, die ein FileAccess.Read-Argument akzeptiert. Also:

    [code]FileStream fs = new FileStream(FileName, FileMode.Open, [b]FileAccess.Read[/b]);[/code]