From 0805756259b8e834a9e4a9a1c9c9474fc92d0498 Mon Sep 17 00:00:00 2001
From: bolero-MURAKAMI <bolero.murakami@gmail.com>
Date: Sun, 14 Aug 2016 16:54:42 +0900
Subject: [PATCH] add carry_to_exp2

---
 sprout/integer.hpp               |  1 +
 sprout/integer/carry_to_exp2.hpp | 75 ++++++++++++++++++++++++++++++++
 2 files changed, 76 insertions(+)
 create mode 100644 sprout/integer/carry_to_exp2.hpp

diff --git a/sprout/integer.hpp b/sprout/integer.hpp
index 0c35f32c..f2f4d2d1 100644
--- a/sprout/integer.hpp
+++ b/sprout/integer.hpp
@@ -10,6 +10,7 @@
 
 #include <sprout/config.hpp>
 #include <sprout/integer/integer_digits.hpp>
+#include <sprout/integer/carry_to_exp2.hpp>
 #include <sprout/integer/static_pow.hpp>
 
 #endif	// #ifndef SPROUT_INTEGER_HPP
diff --git a/sprout/integer/carry_to_exp2.hpp b/sprout/integer/carry_to_exp2.hpp
new file mode 100644
index 00000000..698384fb
--- /dev/null
+++ b/sprout/integer/carry_to_exp2.hpp
@@ -0,0 +1,75 @@
+/*=============================================================================
+  Copyright (c) 2011-2016 Bolero MURAKAMI
+  https://github.com/bolero-MURAKAMI/Sprout
+
+  Distributed under the Boost Software License, Version 1.0. (See accompanying
+  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+=============================================================================*/
+#ifndef SPROUT_INTEGER_CARRY_TO_EXP2_HPP
+#define SPROUT_INTEGER_CARRY_TO_EXP2_HPP
+
+#include <climits>
+#include <limits>
+#include <sprout/config.hpp>
+#include <sprout/bit/cntl0.hpp>
+#include <sprout/bit/popcount.hpp>
+#include <sprout/type_traits/is_sint.hpp>
+#include <sprout/type_traits/is_uint.hpp>
+#include <sprout/type_traits/enabler_if.hpp>
+
+namespace sprout {
+	namespace detail {
+		template<typename IntType>
+		inline SPROUT_CONSTEXPR IntType
+		carry_to_exp2_simpl(IntType x) {
+			return sprout::popcount(x) <= 1 ? x
+				: IntType(1) << (sizeof(IntType) * CHAR_BIT - sprout::cntl0(x))
+				;
+		}
+		template<typename UIntType>
+		inline SPROUT_CONSTEXPR UIntType
+		carry_to_exp2_uimpl(int n) {
+			return !n ? UIntType(0)
+				: UIntType(1) << (sizeof(UIntType) * CHAR_BIT - n)
+				;
+		}
+	}	// namespace detail
+	//
+	// carry_to_exp2
+	//
+	// note: for signed integer
+	//	x == MIN
+	//		--> carry_to_exp2(x) returns x .
+	//	x < 0
+	//		--> carry_to_exp2(x) returns -carry_to_exp2(-x) .
+	//	-(MIN / 2) < x
+	//		--> carry_to_exp2(x) returns MIN .
+	//
+	// note: for unsigned integer
+	//	MAX / 2 + 1 < x
+	//		--> carry_to_exp2(x) returns 0 .
+	//
+	template<
+		typename IntType,
+		typename sprout::enabler_if<sprout::is_sint<IntType>::value>::type = sprout::enabler
+	>
+	inline SPROUT_CONSTEXPR IntType
+	carry_to_exp2(IntType x) {
+		return x == std::numeric_limits<IntType>::min() ? x
+			: x < IntType(0) ? -sprout::detail::carry_to_exp2_simpl(-x)
+			: sprout::detail::carry_to_exp2_simpl(x)
+			;
+	}
+	template<
+		typename UIntType,
+		typename sprout::enabler_if<sprout::is_uint<UIntType>::value>::type = sprout::enabler
+	>
+	inline SPROUT_CONSTEXPR UIntType
+	carry_to_exp2(UIntType x) {
+		return sprout::popcount(x) <= 1 ? x
+			: sprout::detail::carry_to_exp2_uimpl<UIntType>(sprout::cntl0(x))
+			;
+	}
+}	// namespace sprout
+
+#endif	// #ifndef SPROUT_INTEGER_CARRY_TO_EXP2_HPP