LCGの逆関数

calc_inverse.cpp

#include <iostream>
#include <cstdio>

constexpr inline uint64_t calc_pow(uint64_t a, uint64_t n, uint64_t mask) {
    return n == 0 ? 1 :
        (n & 1 ? a : 1) * calc_pow((a*a)&mask, n >> 1, mask);
}
constexpr inline uint64_t calc_inverse(uint64_t mul, uint64_t mask) {
    return calc_pow(mul, mask >> 1, mask);
}
int main() {
    constexpr uint64_t mul = 0x5D588B656C078965;
    constexpr uint64_t add = 0x269EC3;
    constexpr uint64_t mask = -1;

    constexpr uint64_t div = calc_inverse(mul, mask);
    constexpr uint64_t sub = ~(div * add) + 1;

    printf("%lX,%lX\n",div,sub);

    return 0;
}

これ今見て気付いたけどcalc_powでmask使ってない