Re: Some thoughts regarding GSoC

[Daniel Estévez]

El 13/4/22 a las 19:37, Elof Wecksell escribió:

> There was a discussion a while ago regarding how polynomials are used in 
> the different blocks of GRC and GR. At least for GRC, my opinion is that 
> it should be friendly towards new users who might not be programmers. 
> Today, polynomials are entered as an integer, and the size of the 
> polynomial must be entered in another field, even though it could be 
> determined from the polynomial. Example: Mask: 0x8003 K:14 => [15,1,0]
>
> My suggestion is that, at least in GRC, maybe as parallel blocks to the 
> existing, that polynomials are entered in the [15,1,0] fashion, as a 
> Python-list of exponents, and that mask and K are derived from that 
> input, instead of the other way around. This goes for the blocks 
> Scrambler, Descrambler, LFSR-generators, Reed-Solomon FEC, and probably 
> more.

Hi Elof,

I think that's a good idea about making polynomials easier to use. 
However, there is another tricky fact about polynomials, and it is that 
some authors will list p(x), while others will list the "reverse" 
polynomial p(1/x)x^d (here d is the degree of p). I don't know how to 
solve this notation inconsistency, other than with good documentation 
about what notation we use. In some cases there might be a choice which 
is more natural (the polynomial of a multiplicative scrambler, for 
instance, since it's its transfer function in the usual Z-tranform sense).

Additionally, when listing the polynomials in hex (as a mask), some 
authors will omit the leading term (since it's always 1), and some 
authors will omit the independent term (since in most non-degenerate 
cases it's also 1).

In any case, I think that the approach we take should be 
retro-compatible, and not break people's flowgraphs and documentation. 
An approach could be to provide the two kinds of input as alternatives 
in the same block.

Best,
Daniel.

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