[squeak-dev] Re: Reed Solomon Blues

Robert Withers robert.w.withers at gmail.com
Mon Dec 7 12:38:03 UTC 2015


Sorry, forgot to mentionthe test I am using is 
CryptoReedSolomonTest>>#testEncodeAndDecodeRS_15_9. The other 2 
encodeAnd Decode tests have teh wrong sized data at the level they are 
testing. This data needs to be the size of an interleaved block of 4 
chunks that fit the algorithm.

Just to inform you, in RS(9)(15) ,the data block is 4 times 9 nibbles or 
36 nibbles/18 bytes. Foir some reason I am adding 4 bytes of lenght in 
there, I think to differentiate use of different sized RS algorithms.

Robert

On 12/07/2015 07:20 AM, Robert Withers wrote:
> Hi Good morning,
>
> I am trying to port java code implementing Reed-Solomon encoding with 
> a GaloisField and polynomial system. I am currently testing the 
> easiest Mode, which is 9 data symbols, 15 code symbols and 3 symbols 
> of error.  Theer's 2 nibbles to a byte, so a split and join is needed. 
> This all has to do with iteration where the base indexing changes from 
> 0 to 1. I screwed it up in there somewhere and I am struggling to find 
> teh issue. It looks like a complete code review...
>
> Since this is core crypto code, it would be an extra blessing if 
> someone else's eyes were on this code in detail.More tests always help 
> too. Would someone be willing to crawl into the java and squeak code 
> to review, learn and qualify/validate? Also, you would be helping me 
> understand all this polynomial math and where my indexing issue may be.
>
> The failure in Squeak is in the GenericGFPoly>>#divide: method. It 
> runs forever and the quotient/remainder never reduces it's degree. So 
> one of teh math operations is broken & failing. You can run the 
> EncodingTests
>
> I am including a zip of the Java classes I use. This core Reed-Solomon 
> code was written at Google and released open-source. I wrote a test 
> and they pass, so code is working. The latest Cryptography package in 
> the crypto repo is version 48. Please load that and run the 
> CryptoReedSolomonTest to see the infiniteLoop of the polynomial divide.
>
> Let me know if you can help.
>
> Thanks,
> Robert
>



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