topic Re: Calculating the Checksum on a local file in Vault Customization Forum

Calculating the Checksum on a local file

Anonymous — Mon, 09 Dec 2013 16:20:16 GMT

http://forums.autodesk.com/t5/Vault-Customization/API-Doug-s-checksum-function-doesn-t-seem-to-work-for-me/m-p/3093818/highlight/true#M25

The above thread is a dead end, so to repeat AlexF1980 question :

Where is the mentioned C# code sample from "vault mirror"? Doing a exhausted search in the SDK folder reveals nothing??

Any links? Please...

Re: Calculating the Checksum on a local file

minkd — Mon, 09 Dec 2013 21:11:58 GMT

There are a variety of implementations of CRC32 which should all produce the same result, but which can have very different performance characteristics. I think if you google "crc32 c# implementation", you will find one that suits your needs. -Dave

Re: Calculating the Checksum on a local file

Anonymous — Tue, 10 Dec 2013 08:01:26 GMT

"There are a variety of implementations of CRC32"

Couldn't be more true

"which should all produce the same result"

Couldn´t be more wrong ( Based on two days implementation of various algorithms before posting )

Why not simply provide this algorithm? Trespassing ADN territory?

Cheers!

Re: Calculating the Checksum on a local file

minkd — Tue, 10 Dec 2013 22:40:36 GMT

I didn't realize that CRC32 had so many variants - sorry - I mistakenly assumed it was a standard like MD5 or SHA.

But I can't take the code we use in Vault and share it since it is Autodesk's copyrighted Intellectual Property. I would need permission from the lawyers first, and I'm not sure how to go about doing that.

Doug maintains a blog where he posts a variety of samples & tutorials. I recommend searching there.

-Dave

Re: Calculating the Checksum on a local file

Anonymous — Wed, 11 Dec 2013 07:59:06 GMT

Hi Dave.. Cool runnings.. Doug just entered the building Let´s hope the lawyers lay low as it would be suicide to nail him

Anyways : some more stubborn research led me to the origin of cadfish1´s "obfuscated" codesnippet that´s out of autodesk jurisdiction:

http://www.vbaccelerator.com/home/NET/Code/Libraries/CRC32/Crc32.asp

The C# sample will play ball changing types from uint to long.

Re: Calculating the Checksum on a local file

Anonymous — Tue, 07 Nov 2017 11:04:04 GMT

Good afternoon, could you please update the link http://www.vbaccelerator.com/home/NET/Code/Libraries/CRC32/Crc32.asp, because this link doesn't work anymore.

Re: Calculating the Checksum on a local file

Anonymous — Tue, 14 Nov 2017 16:48:39 GMT

Imagine life without web.archive.org

using System;
using System.IO;

namespace Vbaccelerator.Components.Algorithms
{
   /// <summary>
   /// Calculates a 32bit Cyclic Redundancy Checksum (CRC) using the
   /// same polynomial used by Zip.
   /// </summary>
   public class CRC32
   {      
      private UInt32[] crc32Table;
      private const int BUFFER_SIZE = 1024;

      /// <summary>
      /// Returns the CRC32 for the specified stream.
      /// </summary>
      /// <param name="stream">The stream to calculate the CRC32 for</param>
      /// <returns>An unsigned integer containing the CRC32
       calculation</returns>
      public UInt32 GetCrc32(System.IO.Stream stream)
      {
         unchecked
         {
            UInt32 crc32Result;
            crc32Result = 0xFFFFFFFF;
            byte[] buffer = new byte[BUFFER_SIZE];
            int readSize = BUFFER_SIZE;

            int count = stream.Read(buffer, 0, readSize);
            while (count > 0)
            {
               for (int i = 0; i < count; i++)
               {
                  crc32Result = ((crc32Result) >> 8) ^ crc32Table[(buffer[i]) ^
                   ((crc32Result) & 0x000000FF)];
               }
               count = stream.Read(buffer, 0, readSize);
            }
            
            return ~crc32Result;
         }
      }

      /// <summary>
      /// Construct an instance of the CRC32 class, pre-initialising the table
      /// for speed of lookup.
      /// </summary>
      public CRC32()
      {
         unchecked
         {
            // This is the official polynomial used by CRC32 in PKZip.
            // Often the polynomial is shown reversed as 0x04C11DB7.
            UInt32 dwPolynomial = 0xEDB88320;
            UInt32 i, j;

            crc32Table = new UInt32[256];

            UInt32 dwCrc;
            for(i = 0; i < 256; i++)
            {
               dwCrc = i;
               for(j = 8; j > 0; j--)
               {
                  if ((dwCrc & 1)==1)
                  {
                     dwCrc = (dwCrc >> 1) ^ dwPolynomial;
                  }
                  else
                  {
                     dwCrc >>= 1;
                  }
               }
               crc32Table[i] = dwCrc;
            }
         }
      }
   }
}

Re: Calculating the Checksum on a local file

Anonymous — Wed, 15 Nov 2017 11:52:04 GMT

Thanks!