[sdiy] Long LFSRs (Was Psych Tone)

[mskala at ansuz.sooke.bc.ca]

On Mon, 7 Jan 2019, ASSI wrote:
> > The MEH chapter 5h pages include the reference to the derivation of the
> > feedback taps based on “primitive polynomials”.  Since EXOR feedback is
> > anything but “linear”, I don’t understand the terminology “LFSR”, and
> > continue to use “PRBS” (pseudo random binary sequence).
>
> An EXOR is simply multiplication (given the right encoding).  That is what
> allows an LFSR to implement a matrix multiplication with such low hardware
> complexity.

It's also addition, in a different encoding - and that's the reason for
the LFSR to be called linear.  All these "polynomials" are polynomials
defined over the field GF(2), in which the addition operation is the same
thing as XOR on bits.

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before tribes.
https://ansuz.sooke.bc.ca/