// mcpp-standard: https://github.com/Sunrisepeak/mcpp-standard

// license: Apache-2.0

// file: dslings/cpp11/07-constexpr-1.cpp

//

// Exercise/练习: cpp11 | 07 - constexpr | 编译期计算应用示例

//

// Tips/提示: 根据编译器的输出, 修复编译器报错

//

// Docs/文档:

// - https://en.cppreference.com/w/cpp/language/constexpr

//

// Auto-Checker/自动检测命令:

//

// d2x checker constexpr

//

#include <d2x/common.hpp>

#include <iostream>

template <int N>

struct Sum {

static constexpr int value = Sum<N - 1>::value + N;

};

template <>

struct Sum<1> { static constexpr int value = 1; };

constexpr int factorial(int n) {

return n <= 1 ? 1 : n * factorial(n - 1);

}

double pow(double base, int exp) {

return exp == 0 ? 1.0 : base * pow(base, exp - 1);

}

constexpr double mysin(double x) {

//constexpr double PI = 3.14159265358979323846;

//constexpr double radius = x * PI / 180.0;

#define radius(x) (x * 3.14159265358979323846 / 180.0)

// (-1)^n * radius(x)^2n+1 / factorial(2n + 1);

return radius(x)

- pow(radius(x), 3) / factorial(3)

+ pow(radius(x), 5) / factorial(5);

}

int main() {

// 1. 编译期-函数计算

constexpr int fact_10 = factorial(10);

std::cout << "1 * 2 * .. * 10 = " << fact_10 << std::endl;

// 2. 编译期-模板参数计算

constexpr int sum_4 = Sum<4>::value;

std::cout << "1 + 2 + 3 + 4 = " << sum_4 << std::endl;

// 3. 编译期计算示例:

// value是多少时? value! + (1 + 2 + .. + value) > 10000

constexpr int value = 5;

int f = factorial(value);

constexpr int s = Sum<value>::value;

constexpr int ans = f + s;

static_assert(ans > 10000);

// 4. 编译期计算sin值(自动打表) - 时间复杂度O(1)

constexpr double sin30 = mysin(30.0);

std::cout << "mysin(30): " << sin30 << " " << std::endl;

D2X_WAIT

return 0;

}