Sprout/sprout/bit/bit_reverse.hpp

/*=============================================================================
  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_BIT_BIT_REVERSE_HPP
#define SPROUT_BIT_BIT_REVERSE_HPP

#include <climits>
#include <type_traits>
#include <sprout/config.hpp>
#include <sprout/assert.hpp>

namespace sprout {
	namespace detail {
		SPROUT_STATIC_CONSTEXPR unsigned char bit_rev_8_table[std::size_t(UCHAR_MAX) + 1] = {
			0, 128, 64, 192, 32, 160, 96, 224, 16, 144, 80, 208, 48, 176, 112, 240, 8, 136, 72, 200,
			40, 168, 104, 232, 24, 152, 88, 216, 56, 184, 120, 248, 4, 132, 68, 196, 36, 164, 100, 228,
			20, 148, 84, 212, 52, 180, 116, 244, 12, 140, 76, 204, 44, 172, 108, 236, 28, 156, 92, 220,
			60, 188, 124, 252, 2, 130, 66, 194, 34, 162, 98, 226, 18, 146, 82, 210, 50, 178, 114, 242,
			10, 138, 74, 202, 42, 170, 106, 234, 26, 154, 90, 218, 58, 186, 122, 250, 6, 134, 70, 198,
			38, 166, 102, 230, 22, 150, 86, 214, 54, 182, 118, 246, 14, 142, 78, 206, 46, 174, 110, 238,
			30, 158, 94, 222, 62, 190, 126, 254, 1, 129, 65, 193, 33, 161, 97, 225, 17, 145, 81, 209,
			49, 177, 113, 241, 9, 137, 73, 201, 41, 169, 105, 233, 25, 153, 89, 217, 57, 185, 121, 249,
			5, 133, 69, 197, 37, 165, 101, 229, 21, 149, 85, 213, 53, 181, 117, 245, 13, 141, 77, 205,
			45, 173, 109, 237, 29, 157, 93, 221, 61, 189, 125, 253, 3, 131, 67, 195, 35, 163, 99, 227,
			19, 147, 83, 211, 51, 179, 115, 243, 11, 139, 75, 203, 43, 171, 107, 235, 27, 155, 91, 219,
			59, 187, 123, 251, 7, 135, 71, 199, 39, 167, 103, 231, 23, 151, 87, 215, 55, 183, 119, 247,
			15, 143, 79, 207, 47, 175, 111, 239, 31, 159, 95, 223, 63, 191, 127, 255
		};
		template<std::size_t Size>
		struct bit_rev {
		private:
			SPROUT_STATIC_CONSTEXPR std::size_t next_size = Size / 2;
			SPROUT_STATIC_CONSTEXPR std::size_t shift_bits = next_size * CHAR_BIT;
		public:
			template<typename Integral>
			SPROUT_CONSTEXPR Integral
			operator()(Integral x) const {
				return (sprout::detail::bit_rev<next_size>().template operator()(x) << shift_bits)
					| (sprout::detail::bit_rev<next_size>().template operator()(x >> shift_bits))
					;
			}
		};
		template<>
		struct bit_rev<1> {
		public:
			template<typename Integral>
			SPROUT_CONSTEXPR Integral
			operator()(Integral x) const {
				return sprout::detail::bit_rev_8_table[static_cast<unsigned char>(x & UCHAR_MAX)];
			}
		};
	}	// namespace detail
	//
	// bit_reverse
	//
	template<typename Integral>
	SPROUT_CONSTEXPR typename std::enable_if<
		std::is_integral<Integral>::value,
		Integral
	>::type
	bit_reverse(Integral x) {
		typedef typename std::make_unsigned<Integral>::type unsigned_type;
		return static_cast<Integral>(
			sprout::detail::bit_rev<sizeof(Integral)>().template operator()<unsigned_type>(x)
			);
	}
	//
	// bit_reverse_in
	//
	template<typename Integral>
	inline SPROUT_CONSTEXPR typename std::enable_if<
		std::is_integral<Integral>::value,
		Integral
	>::type
	bit_reverse_in(Integral x, int length) {
		typedef typename std::make_unsigned<Integral>::type unsigned_type;
		return SPROUT_ASSERT(length <= sizeof(Integral) * CHAR_BIT),
			static_cast<Integral>(
				sprout::detail::bit_rev<sizeof(Integral)>().template operator()<unsigned_type>(x)
					>> (sizeof(Integral) * CHAR_BIT - length)
				)
			;
	}
}	// namespace sprout

#endif	// #ifndef SPROUT_BIT_BIT_REVERSE_HPP