[sdiy] Long LFSRs (Was Psych Tone)

[Donald Tillman]

On Jan 6, 2019, at 9:16 AM, Donald Tillman <don at till.com> wrote:
> 
> For any given LFSR length, there are one, or more, or a lot more, choices for feedback taps for a maximum length sequence.

I've long forgotten the math behind this, and apparently there is no easy algorithm, so finding the taps for a maximum length sequence might be a brute force operation.

Here's a table of taps:

    Philip Koopman: Maximal Length LFSR Feedback Terms
    http://users.ece.cmu.edu/~koopman/lfsr/

His computations only go to 32 bits long, and he found 67,108,864 combinations of taps for that (the text file lists only the first 100).

Being practical, if you've got a 127 bit shift register, I think you'd do pretty well with just an arbitrary bunch of taps along the length.

  -- Don
--
Donald Tillman, Palo Alto, California
http://www.till.com