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Sprout/sprout/math/log.hpp
2013-02-07 03:32:05 +09:00

66 lines
2 KiB
C++

#ifndef SPROUT_MATH_LOG_HPP
#define SPROUT_MATH_LOG_HPP
#include <cstddef>
#include <limits>
#include <type_traits>
#include <sprout/config.hpp>
#include <sprout/detail/pow.hpp>
#include <sprout/math/detail/config.hpp>
#include <sprout/math/constants.hpp>
#include <sprout/math/factorial.hpp>
#include <sprout/math/sqrt.hpp>
#include <sprout/type_traits/enabler_if.hpp>
namespace sprout {
namespace math {
namespace detail {
template<typename T>
inline SPROUT_CONSTEXPR T
log_impl_1(T x, std::size_t n, std::size_t last) {
return last - n == 1
? (n % 2 ? 1 : -1) * sprout::detail::pow_n(x, n) / n
: sprout::math::detail::log_impl_1(x, n, n + (last - n) / 2)
+ sprout::math::detail::log_impl_1(x, n + (last - n) / 2, last)
;
}
template<typename T>
inline SPROUT_CONSTEXPR T
log_impl(T x) {
return !(x > sprout::math::root_two<T>())
? sprout::math::detail::log_impl_1(x - 1, 1, sprout::math::factorial_limit<T>() + 1)
: 2 * sprout::math::detail::log_impl(sprout::math::sqrt(x))
;
}
template<
typename FloatType,
typename sprout::enabler_if<std::is_floating_point<FloatType>::value>::type = sprout::enabler
>
inline SPROUT_CONSTEXPR FloatType
log(FloatType x) {
typedef double type;
return x == 0 ? std::numeric_limits<FloatType>::quiet_NaN()
: !(x > 0) ? -std::numeric_limits<FloatType>::infinity()
: x < 1 ? static_cast<FloatType>(-sprout::math::detail::log_impl(1 / static_cast<type>(x)))
: static_cast<FloatType>(sprout::math::detail::log_impl(static_cast<type>(x)))
;
}
template<
typename IntType,
typename sprout::enabler_if<std::is_integral<IntType>::value>::type = sprout::enabler
>
inline SPROUT_CONSTEXPR double
log(IntType x) {
return sprout::math::detail::log(static_cast<double>(x));
}
} // namespace detail
using NS_SPROUT_MATH_DETAIL::log;
} // namespace math
using sprout::math::log;
} // namespace sprout
#endif // #ifndef SPROUT_MATH_LOG_HPP