add sprout::exp, log

sprout/math/log.hpp

@@ -0,0 +1,81 @@
+#ifndef SPROUT_MATH_LOG_HPP
+#define SPROUT_MATH_LOG_HPP
+
+#include <cstddef>
+#include <limits>
+#include <type_traits>
+#include <sprout/config.hpp>
+#include <sprout/math/constants.hpp>
+#include <sprout/math/factorial.hpp>
+#include <sprout/math/sqrt.hpp>
+#include <sprout/utility/enabler_if.hpp>
+#if SPROUT_USE_BUILTIN_CMATH_FUNCTION
+#	include <cmath>
+#endif
+
+namespace sprout {
+	namespace math {
+		namespace detail {
+			template<typename T>
+			inline SPROUT_CONSTEXPR T
+			log_impl_2(T x, T tmp, std::size_t n, T xn) {
+				return n > sprout::math::factorial_limit<T>() ? tmp
+					: sprout::math::detail::log_impl_2(
+						x,
+						tmp + (n % 2 ? 1 : -1) * xn / n,
+						n + 1,
+						xn * x
+						)
+					;
+			}
+			template<typename T>
+			inline SPROUT_CONSTEXPR T
+			log_impl_1(T x) {
+				return sprout::math::detail::log_impl_2(
+					x,
+					x,
+					2,
+					x * x
+					);
+			}
+			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)
+					: 2 * sprout::math::detail::log_impl(sprout::math::detail::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>::infinity()
+					: static_cast<FloatType>(sprout::math::detail::log_impl(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
+
+#	if SPROUT_USE_BUILTIN_CMATH_FUNCTION
+		using std::log;
+#	else
+		using sprout::math::detail::log;
+#	endif
+	}	// namespace math
+
+	using sprout::math::log;
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_MATH_LOG_HPP