GeneralHash: the default polynomial isn't really irreducible about rollinghashcpp HOT 4 CLOSED

Suggestion: this polynomial looks nice
http://www.wolframalpha.com/input/?i=factor+x^0+x^1+x^2+x^5+x^6+x^7+x^9+x^11+x^14+x^19+x^20+x^21+x^22+x^24+x^27+x^30+x^32+mod+2

I think there's little advantage in using smaller than 32-bit state for this algorithm, even on 32-bit-only machines (which are rare enough nowadays). In decimal representation it's 1232620263 (if without the x^32 bit).

Apart from being irreducible, it's also primitive, which might have some advantage, but I haven't given much thought to that and I'm really not so good in number theory anyway. I just chose a random line from a public list https://users.ece.cmu.edu/~koopman/lfsr/index.html

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@vcunat

Thank you. I don't know how we ended up with a reducible polynomial. It is slightly embarrassing. I fixed it with the last commit.

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@vcunat

I have moved your other proposal to another issue : #7

You are entirely correct, but I want to distinguish the issues.

Closing this particular one.

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Right, it is better to keep it separate.

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