Same seed produces different noise depending on OS?

[a-day-old-bagel]

I notice that I get different results for the same seed depending on whether I compile in Windows or Linux. Is this a concern?

[Auburn]

It shouldn't do, let me look into it

[Auburn]

I couldn't reproduce the issue, have you got any more details on how you encountered this?

[a-day-old-bagel]

I'll have to look again and see if I can find more details. I was using gcc on Linux and MSVC on Windows, but I'll try to isolate the cause. It could have just been my system or library versions or some random thing.

[vlichevsky]

The cause of this issue seems to be that random number distributions algorithms are implementation-defined. See the discussion at https://www.reddit.com/r/cpp/comments/7i21sn/til_uniform_int_distribution_is_not_portable/. I was able to reproduce the issue on Linux with GCC 7 + libstdc++ vs. Clang 5.0 + libc++.

#include "FastNoise.h"
#include <iostream>
int main(int argc, char* argv[])
{
    int mySeed = 42;
    FastNoise myNoise;
    myNoise.SetSeed(mySeed);
    std::cout << "seed: " << myNoise.GetSeed() << "\n";
    std::cout << "noise: ";
    for (int x = 1; x < 6; ++x) {
        for (int y = 1; y < 6; ++y) {
            std::cout << " " << myNoise.GetNoise(x, y);
        }
    }
    std::cout << "\n";
    return 0;
}

This program prints different sequences, whether it is linked with libstdc++ (version (Debian 7.2.0-17) 7.2.1 20171205) or with libc++ (Debian package version 5.0-1). If I replace std::uniform_int_distribution with boost::random::uniform_int_distribution here: https://github.com/Auburns/FastNoise/blob/f8423d7b5fabea7630712bb13a3d43be36299f8f/FastNoise.cpp#L208, then the program will generate the same sequence, no matter what compiler and standard library were used.

[Auburn]

I just put up a change removing use of std::uniform_int_distribution in favour of std::mt19937_64 and using modulo to get a range, while this isn't a uniform distribution it is using a uint64 so it is very very close. https://github.com/Auburns/FastNoise/commit/b7d77466ade85e2206d0b31e0dd5f20076cce6e6