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https://github.com/bolero-MURAKAMI/Sprout.git
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80 lines
2.7 KiB
C++
80 lines
2.7 KiB
C++
/*=============================================================================
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Copyright (c) 2011-2013 Bolero MURAKAMI
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https://github.com/bolero-MURAKAMI/Sprout
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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=============================================================================*/
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#ifndef SPROUT_BIT_LENGTH_HPP
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#define SPROUT_BIT_LENGTH_HPP
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#include <climits>
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#include <cstddef>
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#include <type_traits>
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#include <sprout/config.hpp>
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namespace sprout {
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namespace detail {
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SPROUT_STATIC_CONSTEXPR std::size_t bit_len_8_table[std::size_t(UCHAR_MAX) + 1] = {
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0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4,
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5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6, 6,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8,
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8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8, 8
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};
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template<std::size_t Size>
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struct bit_len {
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private:
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SPROUT_STATIC_CONSTEXPR std::size_t next_size = Size - 1;
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SPROUT_STATIC_CONSTEXPR std::size_t shift_bits = next_size * CHAR_BIT;
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private:
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template<typename IntType>
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SPROUT_CONSTEXPR IntType
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impl(IntType x, unsigned char i) const {
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return bit_len_8_table[i]
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? bit_len_8_table[i] + next_size * CHAR_BIT
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: sprout::detail::bit_len<next_size>().template operator()(x)
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;
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}
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public:
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template<typename IntType>
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SPROUT_CONSTEXPR IntType
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operator()(IntType x) const {
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return impl(x, static_cast<unsigned char>((x >> shift_bits) & UCHAR_MAX));
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}
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};
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template<>
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struct bit_len<1> {
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public:
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template<typename IntType>
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SPROUT_CONSTEXPR IntType
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operator()(IntType x) const {
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return bit_len_8_table[static_cast<unsigned char>(x & UCHAR_MAX)];
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}
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};
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} // namespace detail
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//
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// bit_length
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//
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template<typename IntType>
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inline SPROUT_CONSTEXPR typename std::enable_if<
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std::is_integral<IntType>::value,
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IntType
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>::type
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bit_length(IntType x) {
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return sprout::detail::bit_len<sizeof(IntType)>().template operator()(x);
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}
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} // namespace sprout
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#endif // #ifndef SPROUT_BIT_LENGTH_HPP
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