Seeding Bias Test

seeding_bias.cpp

/*
 * Seeding Bias Test
 *
 *   - Runs through all possible seeds and examines the output for
 *     bias.  Doing so is only practical for 32-bit (or less) seeds
 *     and 32-bit (or less) output.
 *
 * Compilation note:
 *
 *   - You need to define the following preprocessor symbols to compile this
 *     code:
 *
 *         INCLUDE_FILE   (e.g., <random>, "pcg_random.hpp", etc.)
 *         RNG_TYPE       (e.g., std:mt19937, pcg32_once_insecure, etc.)
 *         SEED_TYPE      (e.g., uint32_t, should be the type of the argument
 *                        to the RNG_TYPE constructor).
 *
 * Note: You can't test pcg32 with this code, since it has a 64-bit seed
 *       argument.
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2019 Melissa E. O'Neill
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */

#include <vector>
#include <iostream>
#include <random>
#include <type_traits>
#include <cstdint>

#ifndef SEED_TYPE
#define SEED_TYPE RNG_TYPE::result_type
#endif

#ifdef INCLUDE_FILE
#include INCLUDE_FILE
#endif

#define STRINGIFY_HELPER(...) #__VA_ARGS__
#define STRINGIFY(...) STRINGIFY_HELPER(__VA_ARGS__)

int main(int argc, char* argv[]) {
    constexpr size_t SEEDS = size_t(~(SEED_TYPE(0))) + 1;
    constexpr size_t OUTPUTS = size_t(RNG_TYPE::max()) + 1;
    size_t DEPTH = argc > 1 ? atoi(argv[1]) : 1;
    std::cout << "Bias test of " STRINGIFY(RNG_TYPE) ":\n"
              << "- Will enumerate through all " << SEEDS
              << " seeds, reading " << DEPTH
              << " outputs from each one.\n";
    using count_type = std::conditional_t<OUTPUTS >= SEEDS, uint8_t, uint32_t>;
    std::vector<count_type> counts(OUTPUTS);
    std::cout << "- Enumerating: " << std::flush;
    for (size_t seed=0; seed < SEEDS; ++seed) {
        RNG_TYPE rng(seed);
        for (size_t i = 0; i < DEPTH; ++i) {
            auto r = rng();
            ++counts[r];
        }
        if ((seed & (SEEDS/64-1)) == (SEEDS/64-1))
            std::cout << "." << std::flush;
    }
    size_t shown = 0;
    std::cout << "\n\nNever occurring: ";
    for (size_t i = 0; i < OUTPUTS; ++i) {
        if (counts[i] == 0) {
            std::cout << i << ", ";
            if (++shown >= 20) {
                std::cout << "...";
                break;
            }
        }
    }
    if (shown == 0)
        std::cout << "(none)";
    std::cout << "\nMost overrepresented: ";
    size_t highrep_count = 0;
    size_t highrep_n = 0;
    for (size_t i = 0; i < OUTPUTS; ++i) {
        if (counts[i] > highrep_count) {
            highrep_n = i;
            highrep_count = counts[i];
        }
    }
    if (highrep_n == 0 && highrep_count == DEPTH*SEEDS/OUTPUTS)
        std::cout << "(nothing overrepresented)\n";
    else
        std::cout << highrep_n << " -- repeated "
                  << highrep_count << " times\n";

    return 0;
}