test/std/numerics/rand/rand.eng/rand.eng.lcong/alg.pass.cpp

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// <random>

// template <class UIntType, UIntType a, UIntType c, UIntType m>
//   class linear_congruential_engine;

// result_type operator()();

#include <random>
#include <cassert>

#include "test_macros.h"

int main(int, char**)
{
    typedef unsigned long long T;

    // m might overflow, but the overflow is OK so it shouldn't use schrage's algorithm
    typedef std::linear_congruential_engine<T, 25214903917ull, 1, (1ull<<48)> E1;
    E1 e1;
    // make sure the right algorithm was used
    assert(e1() == 25214903918);
    assert(e1() == 205774354444503);
    assert(e1() == 158051849450892);
    // make sure result is in bounds
    assert(e1() < (1ull<<48));
    assert(e1() < (1ull<<48));
    assert(e1() < (1ull<<48));
    assert(e1() < (1ull<<48));
    assert(e1() < (1ull<<48));

    // m might overflow. The overflow is not OK and result will be in bounds
    // so we should use shrage's algorithm
    typedef std::linear_congruential_engine<T, (1ull<<2), 0, (1ull<<63) + 1> E2;
    E2 e2;
    // make sure shrage's algorithm is used (it would be 0s otherwise)
    assert(e2() == 4);
    assert(e2() == 16);
    assert(e2() == 64);
    // make sure result is in bounds
    assert(e2() < (1ull<<48) + 1);
    assert(e2() < (1ull<<48) + 1);
    assert(e2() < (1ull<<48) + 1);
    assert(e2() < (1ull<<48) + 1);
    assert(e2() < (1ull<<48) + 1);

    // m will not overflow so we should not use shrage's algorithm
    typedef std::linear_congruential_engine<T, 1ull, 1, (1ull<<48)> E3;
    E3 e3;
    // make sure the correct algorithm was used
    assert(e3() == 2);
    assert(e3() == 3);
    assert(e3() == 4);
    // make sure result is in bounds
    assert(e3() < (1ull<<48));
    assert(e3() < (1ull<<48));
    assert(e3() < (1ull<<48));
    assert(e3() < (1ull<<48));
    assert(e2() < (1ull<<48));

    return 0;
}