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=> 12/22/99 1:00:59 PM EST, djm at san.rr.com =>
<< Does anybody out there have code for generic CRC generation? The 
 implementation does not have to be efficient. I am aware of the 
 16-bit algorithm in the current image, but need to be able to 
 generate CRCs with non-standard polynomials for arbitrary bit length 
 messages. Thanks in advance. >>

Doug,

Attached is CRC package I did a while ago.
I hacked a change to remove BitMasks Class Variable from class Integer;
  it wouldn't load on 2.6 otherwise. 2.7a fixes bug. Much slower table 
  creation without that Class Variable. It cached BitMasks (1-bit in a width 
of 0s).
This is based rather strictly on the paper by Ross N. Williams. 
I built the table driven version and then went back and added   
  the reference version from the paper to fully document the program. 
I later added an 'incremental' version <processes crc's a character at a time,
  but uses tables for calculating intermediate results>.
There are various test methods to execute internal tests; they are probably
  the best way to figure out how to add your own needs to the package..
------------------------------------------
I've taken a quick look at Maurice's package.
His algorithms are based on
  Peterson & Weldon's 'Error Correction Codes'
  so the packages look different when setting up your own crc processor.
His goal of using 30 bits for intermediate results is definitely
  the right way to go for Squeak (with 2 extra bits over SmallInteger in
  a 32-bit word) so I'll have to figure out how he does the algorithm.

Jerry.

+--------------------+
| Jerry L. Archibald |
+--------------------+---------+
| systemObjectivesIncorporated |
+------------------------------+

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0,2665,2,8040,0,

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