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Wed Nov 7 19:58:48 EST 2012

2 forms of LFSRs

Fibonacci:

  shifts IN a bit based on the XOR of a pattern[1]

Galois: a direct implementation of multiplication by x to produce a
sequence 1,x,x^2, ... modulo p(x)

  take the bit that shifts out and use to contidionally XOR the lower
  coefficients of the polynomial with the state vector (Used in
  Staapl).

The former is a Fibonacci LFSR, while the latter is a Galois LFSR.
Both are easy in hardware, but the latter is easy in software due to
the availability of a "conditional parallel XOR".


[1] http://en.wikipedia.org/wiki/Linear_feedback_shift_register


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