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
28template <class T>
29inline
30T
31sqr(T x)
32{
33 return x*x;
34}
35
36double
37f(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
42int 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(x: v);
61 }
62 std::sort(first: u.begin(), last: 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(first: b, last: b + Np + 1, val: 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

source code of libcxx/test/std/numerics/rand/rand.dist/rand.dist.samp/rand.dist.samp.plinear/eval_param.pass.cpp