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maths: add factorial and combination

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This commit is contained in:
Danny Robson 2015-02-02 15:25:22 +11:00
parent a81b30c685
commit ebd1087087
1 changed files with 26 additions and 1 deletions
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27
maths.hpp
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@ -20,8 +20,10 @@
#ifndef __MATHS_HPP #ifndef __MATHS_HPP
#define __MATHS_HPP #define __MATHS_HPP
#include <cstdint>
#include <type_traits> #include <type_traits>
#include <utility> #include <utility>
#include <cmath>
template <typename T> template <typename T>
T T
@ -168,7 +170,8 @@ exactly_zero [[gnu::pure]] (T a)
constexpr double PI_d = 3.141592653589793238462643; constexpr double PI_d = 3.141592653589793238462643;
constexpr float PI_f = 3.141592653589793238462643f; constexpr float PI_f = 3.141592653589793238462643f;
//----------------------------------------------------------------------------- constexpr float E_f = 2.71828182845904523536028747135266250f;
constexpr double constexpr double
to_degrees [[gnu::pure]] (double radians) { to_degrees [[gnu::pure]] (double radians) {
return radians * 180 / PI_d; return radians * 180 / PI_d;
@ -194,6 +197,28 @@ to_radians [[gnu::pure]] (double degrees) {
} }
//-----------------------------------------------------------------------------
constexpr uintmax_t
factorial [[gnu::pure]] (unsigned i)
{
return i <= 1 ? 0 : i * factorial (i - 1);
}
constexpr uintmax_t
stirling [[gnu::pure]] (unsigned n)
{
return static_cast<uintmax_t> (std::sqrt (2 * PI_f * n) * std::pow (n / E_f, n));
}
constexpr uintmax_t
combination [[gnu::pure]] (unsigned n, unsigned k)
{
return factorial (n) / (factorial (k) / (factorial (n - k)));
}
//----------------------------------------------------------------------------- //-----------------------------------------------------------------------------
/// Variadic minimum /// Variadic minimum
template <typename T> template <typename T>