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 // REQUIRES: long_tests
10 
11 // <random>
12 
13 // template<class RealType = double>
14 // class piecewise_linear_distribution
15 
16 // template<class _URNG> result_type operator()(_URNG& g, const param_type& parm);
17 
18 #include <algorithm>   // for sort
19 #include <cassert>
20 #include <cmath>
21 #include <cstddef>
22 #include <limits>
23 #include <random>
24 #include <vector>
25 
26 #include "test_macros.h"
27 
28 template <class T>
29 inline
30 T
31 sqr(T x)
32 {
33     return x*x;
34 }
35 
36 double
37 f(double x, double a, double m, double b, double c)
38 {
39     return a + m*(sqr(x) - sqr(b))/2 + c*(x-b);
40 }
41 
42 int main(int, char**)
43 {
44     {
45         typedef std::piecewise_linear_distribution<> D;
46         typedef D::param_type P;
47         typedef std::mt19937_64 G;
48         G g;
49         double b[] = {10, 14, 16, 17};
50         double p[] = {25, 62.5, 12.5, 0};
51         const std::size_t Np = sizeof(p) / sizeof(p[0]) - 1;
52         D d;
53         P pa(b, b+Np+1, p);
54         const std::size_t N = 1000000;
55         std::vector<D::result_type> u;
56         for (std::size_t i = 0; i < N; ++i)
57         {
58             D::result_type v = d(g, pa);
59             assert(10 <= v && v < 17);
60             u.push_back(v);
61         }
62         std::sort(u.begin(), u.end());
63         std::ptrdiff_t kp = -1;
64         double a = std::numeric_limits<double>::quiet_NaN();
65         double m = std::numeric_limits<double>::quiet_NaN();
66         double bk = std::numeric_limits<double>::quiet_NaN();
67         double c = std::numeric_limits<double>::quiet_NaN();
68         std::vector<double> areas(Np);
69         double S = 0;
70         for (std::size_t i = 0; i < areas.size(); ++i)
71         {
72             areas[i] = (p[i]+p[i+1])*(b[i+1]-b[i])/2;
73             S += areas[i];
74         }
75         for (std::size_t i = 0; i < areas.size(); ++i)
76             areas[i] /= S;
77         for (std::size_t i = 0; i < Np+1; ++i)
78             p[i] /= S;
79         for (std::size_t i = 0; i < N; ++i)
80         {
81           std::ptrdiff_t k = std::lower_bound(b, b + Np + 1, u[i]) - b - 1;
82           if (k != kp) {
83             a = 0;
84             for (int j = 0; j < k; ++j)
85               a += areas[j];
86             m  = (p[k + 1] - p[k]) / (b[k + 1] - b[k]);
87             bk = b[k];
88             c  = (b[k + 1] * p[k] - b[k] * p[k + 1]) / (b[k + 1] - b[k]);
89             kp = k;
90             }
91           assert(std::abs(f(u[i], a, m, bk, c) - double(i) / N) < .0013);
92         }
93     }
94 
95   return 0;
96 }
97