[Coco] Coco OS9 Source Control (question)

[Christopher R. Hawks]

On Mon, 16 Jun 2014 20:30:12 -0400
Gene Heskett <gheskett at wdtv.com> wrote:

> On Monday 16 June 2014 19:56:41 Greg Law did opine
> And Gene did reply:
> > If you are writing this in C, load the text file into a contiguous
> > block of memory then call crc() with the starting address and size
> > of the file. This returns a 3-byte CRC that can be converted to say
> > a hex string with printf().
> > 
> > If you don't have sufficient memory to load the entire file in one
> > shot, you can also load the file in say 8K chunks and keep calling
> > crc() with each loaded chunk to accumulate the final CRC.
> > 
> > If you look up the F$CRC system call, you'll see that it has these
> > input parameters:
> > 
> > X = starting address
> > Y = number of bytes
> > U = address of the 3-byte CRC accumulator
> > 
> > The gist is that you need to initialize the CRC accumulator with
> > zeroes
> 
> This may not be correct, ISTR it needs an initial seed value, and its
> not zero's.  But this is being drug up from memory thats near 20
> years old too.

	Manual sez $FFFFFF

> > once and only once before you begin calculating the CRC for each
> > file. Each subsequent call to F$CRC will continue accumulating the
> > CRC into the 3-byte accumulator. After you've called F$CRC for the
> > last chunk of the file, the CRC of the file is the 3-byte value in
> > the accumulator.
> > 
> > I don't have the C compiler manual with me to confirm, but I think
> > crc() is a thin wrapper around the F$CRC system call and takes all
> > three parameters as inputs.
> > 
> > -----Original Message-----
> > From: Bill Pierce via Coco
> > Sent: Monday, June 16, 2014 6:55 PM
> > To: coco at maltedmedia.com
> > Subject: Re: [Coco] Coco OS9 Source Control (question)
> > 
> > 
> > Thanks Gene, is the syscall and access method in the vfy source?
> > I need to make the checksum into a short ASCII string to add as a
> > file extension for easy ID and searching. It alsohas to be added to
> > the checksum report file.
> > 
> > 
> > Bill Pierce
> > "Today is a good day... I woke up" - Ritchie Havens
> > 
> > 
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> > 
> > 
> > 
> > 
> > -----Original Message-----
> > From: Gene Heskett <gheskett at wdtv.com>
> > To: coco <coco at maltedmedia.com>
> > Sent: Mon, Jun 16, 2014 6:11 pm
> > Subject: Re: [Coco] Coco OS9 Source Control (question)
> > 
> > 
> > On Monday 16 June 2014 17:55:38 Bill Pierce via Coco did opine
> > And Gene did reply:
> > (nitr)os9 has a syscall to do that.  Thats how I did the updates, if
> > required, in vfy.  No sense in re-inventing that particular
> > wheel. :)
> > 
> > 
> > Cheers, Gene Heskett
> 
> 
> Cheers, Gene Heskett




Christopher R. Hawks
HAWKSoft
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