97 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// REQUIRES: long_tests10 11// <random>12 13// template<class RealType = double>14// class piecewise_linear_distribution15 16// template<class _URNG> result_type operator()(_URNG& g, const param_type& parm);17 18#include <algorithm> // for sort19#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>29inline30T31sqr(T x)32{33 return x*x;34}35 36double37f(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(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