Re: Jak działa rotr16 w c?

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#217318

From: osobli...
Date: Sun, 03 Jan 2021 21:29

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niedziela, 3 stycznia 2021 o 18:24:30 UTC+1 Mateusz Viste napisał(a):
> 2021-01-03 o 07:07 -0800, osobli...@gmail.com napisał: 
> > Jaki będzie rezultat rotr16(15,2). Czy będzie to 1111, czy 
> > 110000000000000011?
> rotr16() to nie C. 
> 
> Jeśli pytanie dotyczy specyficznego Microsoftowego rozszerzenia, to 
> dokumentacja jest tutaj: 
> https://docs.microsoft.com/en-us/cpp/intrinsics/rotr8-rotr16?view=msvc-160 
> 
> Mateusz

To dotyczy tej pracy:

https://www.pcg-random.org/pdf/hmc-cs-2014-0905.pdf

Tam są używane rotate64. Kod jednego z generatorów, który mnie interesuje wygląda tak:

uint32_t rot1 = (uint32_t)(state >> 122u);
    uint64_t high = (uint64_t)(state >> 64u);
    uint64_t low  = (uint64_t)state;
    uint64_t xored = high ^ low;
    uint64_t newlow  = pcg_rotr_64(xored, rot1);
    uint64_t newhigh = pcg_rotr_64(high, newlow & 63u);
    return (((pcg128_t)newhigh) << 64u) | newlow;

Chcę wiedzieć co tam jest robione, żeby napisać taki rotate poprawnie w Pythonie. Ten sam generator XSL-RR-RR jest też wymieniony tutaj:

https://en.wikipedia.org/wiki/Permuted_congruential_generator

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