Minimal fast random number generation, for simulation purposes. Not cryptographically secure.

minimal-random.cpp

#include <cstdint>

// Random 32-bit unsigned integer.
uint32_t pcg32(uint64_t& rng) {
  rng = rng * 6364136223846793005ULL + 1;
  int rot = rng >> 59u;
  uint32_t r = (rng >> 18u) ^ rng;
  return (r >> rot) | (r << (32 - rot));
}

// Random double on [0, 1), assuming IEEE754.
double uniform(uint64_t& rng) {
    union { double d; uint64_t i; } u { 1.0 };
    u.i |= (uint64_t(pcg32(rng)) << 20) ^ pcg32(rng);
    return u.d - 1.0;
}

#include <iostream>
#include <ctime>
int main(int argc, char** argv) {
    uint64_t rng = std::time(0); // Seed with time or constant value.
    for (int i = 0; i < 10; ++i) std::cout << std::hex << pcg32(rng) << " ";
    std::cout << "\n";
    for (int i = 0; i < 10; ++i) std::cout << uniform(rng) << " ";
    std::cout << "\n";
    return 0;
}