[ecc] Decoding different (N,K) combinations

[Nimrod Mesika <nimrodm@bezeqint.net>]

I'm having trouble implementing the Chien search algorithm for
shortened codewords (i.e., N<255 for GF(256)).

It seems like I can do one of the following:

o Start the search from the last byte of the codeword (the lowest
  power of alpha, alpha^(-1)) and proceed up to alpha^(-N). Thus,
  the output will be in reverse order with respect to the input of
  the decoder.

o Start the search from alpha^(-N) and proceed to alpha^(-1). This
  is simple if N is constant. However, if N may be different for
  different codewords, another set of (non-constant) multipliers are
  necessary so that coefficients of lambda(x) and omega(x) will be
  multiplied by alpha^(-N) before the search starts. 

  Of course, this method also requires a ROM table of alpha^(-N)
  for every possible N.


I was wondering if there is a simpler method? Anyone?

I'll be happy to provide my C code and (almost finished) verilog
code.

-- 
Nimrod.

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