[sdiy] LFSR using lookup tables

[John Ames]

Yeah, it's possible that multiple-precision arithmetic (i.e. LFSR
sizes larger than native word size) change the equation significantly,
at least provided that the target architecture supports *indexing* by
larger than native word size. On 8-bit architectures I could easily
see this being the case.

On 2/19/20, Ben Stuyts <ben at stuyts.nl> wrote:
> Hi Tom,
>
> Your link was the first I looked up after watching that video, as your noise
> pic’s were the first thing that came to my mind. :-)
>
> Ben
>
>
>> On 19 Feb 2020, at 15:17, Tom Wiltshire <tom at electricdruid.net> wrote:
>>
>> I shall be interested to hear how you get on, Ben.
>>
>> I *love* a nice look-up table. My first rule is “Don’t do hard sums!”,
>> which means “pretty much anything beyond an addition”!
>>
>> I suspect for the very-lower-level stuff I’ve been doing, the table
>> overhead is worse than the alternative (doing shifts of the LFSR one byte
>> at a time, as described here:
>> https://electricdruid.net/practical-lfsr-random-number-generators/
>> <https://electricdruid.net/practical-lfsr-random-number-generators/>). But
>> it’d great if it wasn’t!
>>
>>> On 19 Feb 2020, at 13:43, Ben Stuyts <ben at stuyts.nl
>>> <mailto:ben at stuyts.nl>> wrote:
>>>
>>> I just watched this interesting talk about using lookup tables (in
>>> hardware and software): https://www.youtube.com/watch?v=LnqqvVp_UZg
>>> <https://www.youtube.com/watch?v=LnqqvVp_UZg>
>>>
>>> At the very last end (around 29:11 minutes) he starts talking about
>>> LFSR's and maximising their performance using lookup tables instead of
>>> the more conventional XOR method. He has a 6 times performance increase.
>>> Very cool, I’m going to try this out soon.
>>>
>>> Ben
>>>
>>>
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>>
>
>