xref: /llvm-project/libcxx/test/std/numerics/rand/rand.eng/rand.eng.lcong/default.pass.cpp (revision ba87515fea90b5d55836a8e3be63a7e683ce299d)
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 // linear_congruential_engine();
15 
16 #include <random>
17 #include <cassert>
18 #include <climits>
19 
20 #include "test_macros.h"
21 
22 template <class T, T a, T c, T m>
23 void
24 test1()
25 {
26     typedef std::linear_congruential_engine<T, a, c, m> LCE;
27     LCE e1;
28     LCE e2;
29     e2.seed();
30     assert(e1 == e2);
31 }
32 
33 template <class T>
34 void
35 test()
36 {
37   const int W = sizeof(T) * CHAR_BIT;
38   const T M(static_cast<T>(-1));
39   const T A(static_cast<T>((static_cast<T>(1) << (W / 2)) - 1));
40 
41   // Cases where m = 0
42   test1<T, 0, 0, 0>();
43   test1<T, A, 0, 0>();
44   test1<T, 0, 1, 0>();
45   test1<T, A, 1, 0>();
46 
47   // Cases where m = 2^n for n < w
48   test1<T, 0, 0, 256>();
49   test1<T, 5, 0, 256>();
50   test1<T, 0, 1, 256>();
51   test1<T, 5, 1, 256>();
52 
53   // Cases where m is odd and a = 0
54   test1<T, 0, 0, M>();
55   test1<T, 0, M - 2, M>();
56   test1<T, 0, M - 1, M>();
57 
58   // Cases where m is odd and m % a <= m / a (Schrage)
59   test1<T, A, 0, M>();
60   test1<T, A, M - 2, M>();
61   test1<T, A, M - 1, M>();
62 }
63 
64 template <class T>
65 void test_ext() {
66   const T M(static_cast<T>(-1));
67 
68   // Cases where m is odd and m % a > m / a
69   test1<T, M - 2, 0, M>();
70   test1<T, M - 2, M - 2, M>();
71   test1<T, M - 2, M - 1, M>();
72   test1<T, M - 1, 0, M>();
73   test1<T, M - 1, M - 2, M>();
74   test1<T, M - 1, M - 1, M>();
75 }
76 
77 int main(int, char**)
78 {
79     test<unsigned short>();
80     test_ext<unsigned short>();
81     test<unsigned int>();
82     test_ext<unsigned int>();
83     test<unsigned long>();
84     test_ext<unsigned long>();
85     test<unsigned long long>();
86     // This isn't implemented on platforms without __int128
87 #ifndef TEST_HAS_NO_INT128
88     test_ext<unsigned long long>();
89 #endif
90 
91     return 0;
92 }
93