[Coco] Coco OS9 Source Control (question)

[Gene Heskett]

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.

> 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
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