From 4b3d4e82d7ba92a854a132b3d03735482c99ab90 Mon Sep 17 00:00:00 2001
From: bolero-MURAKAMI <bolero.murakami@gmail.com>
Date: Thu, 7 Feb 2013 03:32:05 +0900
Subject: [PATCH] fix math::exp implementation

---
 sprout/math/exp.hpp | 20 +++++++++++---------
 sprout/math/log.hpp |  2 +-
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/sprout/math/exp.hpp b/sprout/math/exp.hpp
index 148f41e3..7d8cf21f 100644
--- a/sprout/math/exp.hpp
+++ b/sprout/math/exp.hpp
@@ -14,13 +14,18 @@ namespace sprout {
 		namespace detail {
 			template<typename T>
 			inline SPROUT_CONSTEXPR T
-			exp_impl(T x, std::size_t n, std::size_t last) {
+			exp_impl_1(T x, std::size_t n, std::size_t last) {
 				return last - n == 1
 					? sprout::detail::pow_n(x, n) / sprout::math::factorial<T>(n)
-					: sprout::math::detail::exp_impl(x, n, n + (last - n) / 2)
-						+ sprout::math::detail::exp_impl(x, n + (last - n) / 2, last)
+					: sprout::math::detail::exp_impl_1(x, n, n + (last - n) / 2)
+						+ sprout::math::detail::exp_impl_1(x, n + (last - n) / 2, last)
 					;
 			}
+			template<typename T>
+			inline SPROUT_CONSTEXPR T
+			exp_impl(T x) {
+				return 1 + sprout::math::detail::exp_impl_1(x, 1, sprout::math::factorial_limit<T>() + 1);
+			}
 
 			template<
 				typename FloatType,
@@ -29,12 +34,9 @@ namespace sprout {
 			inline SPROUT_CONSTEXPR FloatType
 			exp(FloatType x) {
 				typedef double type;
-				return static_cast<FloatType>(
-					type(1) + sprout::math::detail::exp_impl(
-						static_cast<type>(x),
-						1, sprout::math::factorial_limit<type>() + 1
-						)
-					);
+				return !(x > -1) ? 1 / sprout::math::detail::exp_impl(-static_cast<type>(x))
+					: sprout::math::detail::exp_impl(static_cast<type>(x))
+					;
 			}
 
 			template<
diff --git a/sprout/math/log.hpp b/sprout/math/log.hpp
index ee2969b7..b265e7e2 100644
--- a/sprout/math/log.hpp
+++ b/sprout/math/log.hpp
@@ -42,7 +42,7 @@ namespace sprout {
 				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(type(1) / static_cast<type>(x)))
+					: 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)))
 					;
 			}