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

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 // <random>
  10
  11 // template <class UIntType, UIntType a, UIntType c, UIntType m>
  12 //   class linear_congruential_engine;
  13
  14 // result_type operator()();
  15
  16 #include <random>
  17 #include <cassert>
  18
  19 #include "test_macros.h"
  20
  21 int main(int, char**)
  22 {
  23     typedef unsigned long long T;
  24
  25     // m might overflow, but the overflow is OK so it shouldn't use schrage's algorithm
  26     typedef std::linear_congruential_engine<T, 25214903917ull, 1, (1ull<<48)> E1;
  27     E1 e1;
  28     // make sure the right algorithm was used
  29     assert(e1() == 25214903918);
  30     assert(e1() == 205774354444503);
  31     assert(e1() == 158051849450892);
  32     // make sure result is in bounds
  33     assert(e1() < (1ull<<48));
  34     assert(e1() < (1ull<<48));
  35     assert(e1() < (1ull<<48));
  36     assert(e1() < (1ull<<48));
  37     assert(e1() < (1ull<<48));
  38
  39     // m might overflow. The overflow is not OK and result will be in bounds
  40     // so we should use shrage's algorithm
  41     typedef std::linear_congruential_engine<T, (1ull<<2), 0, (1ull<<63) + 1> E2;
  42     E2 e2;
  43     // make sure shrage's algorithm is used (it would be 0s otherwise)
  44     assert(e2() == 4);
  45     assert(e2() == 16);
  46     assert(e2() == 64);
  47     // make sure result is in bounds
  48     assert(e2() < (1ull<<48) + 1);
  49     assert(e2() < (1ull<<48) + 1);
  50     assert(e2() < (1ull<<48) + 1);
  51     assert(e2() < (1ull<<48) + 1);
  52     assert(e2() < (1ull<<48) + 1);
  53
  54     // m will not overflow so we should not use shrage's algorithm
  55     typedef std::linear_congruential_engine<T, 1ull, 1, (1ull<<48)> E3;
  56     E3 e3;
  57     // make sure the correct algorithm was used
  58     assert(e3() == 2);
  59     assert(e3() == 3);
  60     assert(e3() == 4);
  61     // make sure result is in bounds
  62     assert(e3() < (1ull<<48));
  63     assert(e3() < (1ull<<48));
  64     assert(e3() < (1ull<<48));
  65     assert(e3() < (1ull<<48));
  66     assert(e2() < (1ull<<48));
  67
  68     return 0;
  69 }