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Date: Thu, 16 Aug 2001 15:59:50 +0100
To: "Earl F. Glynn" <efg2@efg2.com>
From: Ted =?iso-8859-1?Q?T=F8raasen?= <ted@biip.no>
Subject: Re: Computer Lab Feedback
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HI , sorry about this delayed feed back.
Regarding the suggestion under, i got it working after making some changes .

I changed Nbyte and I to longoword.
Same with CRCvalue, but guess this part was not needed.

All in all it solved my problem , thank you very much.
You may wanne oppdate the code on the web in case anyone else tries to use
the code.

Again Thank you

Kind Regards
Ted

PROCEDURE CalcCRC16 (p:  pointer; nbyte:  Longword; VAR CRCvalue:  Longword);
     VAR
       i:  longWORD; // Changed to longword from word
       q:  ^buffer;

    {The following is a little cryptic (but executes very quickly).
     The algorithm is as follows:
       1.  exclusive-or the input byte with the low-order byte of
           the CRC register to get an INDEX
       2.  shift the CRC register eight bits to the right
       3.  exclusive-or the CRC register with the contents of
           Table[INDEX]
       4.  repeat steps 1 through 3 for all bytes}
   BEGIN
     q := p;
     FOR   i := 1 TO nBYTE DO
       CRCvalue := Hi(CRCvalue)  XOR  Table[ q^[i] XOR Lo(CRCvalue) ]
   END {CalcCRC16};


At 22:55 2001.07.05 -0500, you wrote:
>Hi, Ted:
>
> > I have been working on a project that needed CRC-16 , and used your CRC-16
> > / CRC-32 Calculator code .
> > This worked great for a while, but there seems to be some limitation on
>the
> > length of the string. Atleast I'm told that the crc value is
> > invalide (verified by a third party) when the string is longer then a
> > limit. No found how long yet but seems to be around 634KB string.
>
>CRC-16 should fail somewhere around 64K-1 = 65535 bytes.
>
> > Was
> > wondering if this is a limitation of the CR-16 or if there might be an
> > error in the source. I'm using D5 sp3.  Hope you are able to give me some
> > feed back on this.
>
>The nbyte parameter passed to the CalcCRC16 procedure is a WORD.
>This means that only values 0 to 65535 are possible with a WORD.
>If you change the type of the nbyte parameter to a DWORD (or a
>LongWord), that will allow lengths of about 2 billion bytes.  I think
>that's all you need to change.
>
>I hope this gets you going.
>
>Best wishes,
>
>--
>efg -- Earl F. Glynn, Overland Park, KS  USA
>efg's Computer Lab Mirror:  http://homepages.borland.com/efg2lab