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