💿🐜 Antkeeper source code
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201 lines
4.8 KiB
201 lines
4.8 KiB
/*
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* Copyright (C) 2020 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef ANTKEEPER_BIT_MATH_HPP
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#define ANTKEEPER_BIT_MATH_HPP
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namespace dna
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{
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/**
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* Reads bits from the least significant bits of a value and returns them in the positions marked by a mask.
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*
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* @param x Value from which bits should be read.
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* @param mask Bit mask indicating where bits should be deposited.
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* @return Bits from the least significant bits of @p x in the positions marked by @p mask.
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*/
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template <class T>
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constexpr T bit_deposit(T x, T mask) noexcept;
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/**
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* Reads bits from a value in the positions marked by a mask and returns them in the least significant bits.
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*
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* @param x Value from which bits should be read.
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* @param mask Bit mask indicating which bits to extract.
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* @return Bits of @p x from the positions marked by @p mask in the least significant bits.
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*/
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template <class T>
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constexpr T bit_extract(T x, T mask) noexcept;
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/**
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* Returns the number of set bits in a value, known as a *population count* or *Hamming weight*.
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*
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* @param x Value to count.
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* @return Number of set bits in @p x.
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*/
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template <typename T>
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constexpr int popcount(T x) noexcept;
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/**
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* Returns the number of differing bits between two values, known as *Hamming distance*.
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*
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* @param x First value.
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* @param y Second value.
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* @return Hamming distance between @px and @p y.
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*/
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template <typename T>
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constexpr int hamming_distance(T x, T y) noexcept;
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template <typename T>
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constexpr T bit_merge(T a, T b, T mask) noexcept
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{
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return a ^ ((a ^ b) & mask);
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}
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template <class T>
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constexpr T bit_pad(T x) noexcept
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{
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x &= (1 << (sizeof(T) << 2)) - 1;
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if constexpr(sizeof(T) >= 8)
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x = (x ^ (x << 16)) & T(0x0000ffff0000ffff);
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if constexpr(sizeof(T) >= 4)
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x = (x ^ (x << 8)) & T(0x00ff00ff00ff00ff);
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if constexpr(sizeof(T) >= 2)
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x = (x ^ (x << 4)) & T(0x0f0f0f0f0f0f0f0f);
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x = (x ^ (x << 2)) & T(0x3333333333333333);
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x = (x ^ (x << 1)) & T(0x5555555555555555);
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return x;
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}
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template <typename T>
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constexpr T bit_interleave(T a, T b) noexcept
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{
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return (bit_pad(b) << 1) | bit_pad(a);
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}
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template <typename T>
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constexpr T bit_swap_adjacent(T x) noexcept
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{
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return ((x & T(0xaaaaaaaaaaaaaaaa)) >> 1) | ((x & T(0x5555555555555555)) << 1);
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}
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template <typename T>
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constexpr T bit_shuffle_adjacent(T x, T mask) noexcept
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{
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T y = bit_swap_adjacent(x);
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return bit_merge(x, y, bit_interleave<T>(mask, mask));
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}
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/**
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* Shuffles the adjacent bits of a value.
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*
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* @param x Value to shuffle.
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* @param g Uniform random bit generator.
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* @return Value with adjacent bits shuffled.
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*/
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/*
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template <class T, class URBG>
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constexpr T bit_shuffle_adjacent(T x, URBG&& g) noexcept
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{
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return bit_swap_adjacent(x, static_cast<T>(g()));
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}*/
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/**
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*
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*/
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template <class T, class U>
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U bit_splice(T a, T b, U mask)
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{
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return bit_deposit(static_cast<U>(a), ~mask) | bit_deposit(static_cast<U>(b), mask);
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}
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/**
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* For an n-bit number with r set bits, there are `n! / ((n - r)! * r!)` permutations.
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*/
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template <class T>
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T next_bit_permutation(T x)
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{
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T y = (x | (x - 1)) + 1;
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return y | ((((y & -y) / (x & -x)) >> 1) - 1);
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}
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template <class T>
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constexpr T bit_deposit(T x, T mask) noexcept
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{
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T result = 0;
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for (T i = 1; mask; i <<= 1)
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{
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if (x & i)
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result |= mask & -mask;
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mask &= mask - 1;
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}
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return result;
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}
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template <class T>
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constexpr T bit_extract(T x, T mask) noexcept
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{
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T result = 0;
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for (T i = 1; mask; i <<= 1)
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{
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if (x & mask & -mask)
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result |= i;
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mask &= mask - 1;
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}
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return result;
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}
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template <typename T>
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constexpr int popcount(T x) noexcept
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{
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int n = 0;
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for (; x; ++n)
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x &= x - 1;
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return n;
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}
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template <typename T>
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inline constexpr int hamming_distance(T x, T y) noexcept
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{
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return popcount(x ^ y);
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}
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/**
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*
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* @param mask Least significant bits indicate whether to inherit the first (0) or second (1) allele from @p a. Most significant bits indicate whether to inherit the first (0) or second (1) allele from @p b.
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*/
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template <class T>
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constexpr T inherit(T a, T b, T mask) noexcept
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{
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a = bit_shuffle_adjacent<T>(a, mask);
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b = bit_shuffle_adjacent<T>(b, mask >> (sizeof(T) << 2));
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return bit_merge<T>(a, b, T(0x5555555555555555));
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}
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} // namespace dna
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#endif // ANTKEEPER_BIT_MATH_HPP
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