1//===----------------------------------------------------------------------===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is dual licensed under the MIT and the University of Illinois Open
6// Source Licenses. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// REQUIRES: long_tests
11
12// <random>
13
14// template<class RealType = double>
15// class piecewise_linear_distribution
16
17// template<class _URNG> result_type operator()(_URNG& g, const param_type& parm);
18
19#include <random>
20#include <vector>
21#include <iterator>
22#include <numeric>
23#include <cassert>
24
25template <class T>
26inline
27T
28sqr(T x)
29{
30    return x*x;
31}
32
33double
34f(double x, double a, double m, double b, double c)
35{
36    return a + m*(sqr(x) - sqr(b))/2 + c*(x-b);
37}
38
39int main()
40{
41    {
42        typedef std::piecewise_linear_distribution<> D;
43        typedef D::param_type P;
44        typedef std::mt19937_64 G;
45        G g;
46        double b[] = {10, 14, 16, 17};
47        double p[] = {25, 62.5, 12.5, 0};
48        const size_t Np = sizeof(p) / sizeof(p[0]) - 1;
49        D d;
50        P pa(b, b+Np+1, p);
51        const int N = 1000000;
52        std::vector<D::result_type> u;
53        for (int i = 0; i < N; ++i)
54        {
55            D::result_type v = d(g, pa);
56            assert(10 <= v && v < 17);
57            u.push_back(v);
58        }
59        std::sort(u.begin(), u.end());
60        int kp = -1;
61        double a;
62        double m;
63        double bk;
64        double c;
65        std::vector<double> areas(Np);
66        double S = 0;
67        for (int i = 0; i < areas.size(); ++i)
68        {
69            areas[i] = (p[i]+p[i+1])*(b[i+1]-b[i])/2;
70            S += areas[i];
71        }
72        for (int i = 0; i < areas.size(); ++i)
73            areas[i] /= S;
74        for (int i = 0; i < Np+1; ++i)
75            p[i] /= S;
76        for (int i = 0; i < N; ++i)
77        {
78            int k = std::lower_bound(b, b+Np+1, u[i]) - b - 1;
79            if (k != kp)
80            {
81                a = 0;
82                for (int j = 0; j < k; ++j)
83                    a += areas[j];
84                m = (p[k+1] - p[k]) / (b[k+1] - b[k]);
85                bk = b[k];
86                c = (b[k+1]*p[k] - b[k]*p[k+1]) / (b[k+1] - b[k]);
87                kp = k;
88            }
89            assert(std::abs(f(u[i], a, m, bk, c) - double(i)/N) < .001);
90        }
91    }
92}
93