BitSet.h

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#pragma once
// SPDX-FileCopyrightText: 2025 Nessan Fitzmaurice <nzznfitz+gh@icloud.com>
// SPDX-License-Identifier: MIT

 
#include <gf2/BitStore.h>
#include <gf2/BitSpan.h>
 
namespace gf2 {

template<usize N, unsigned_word Word = usize>
class BitSet : public BitStore<BitSet<N, Word>> {
private:
    // The bit elements are packed compactly into this standard array of unsigned words
    std::array<Word, words_needed<Word>(N)> m_data{};
 
public:
    using word_type = Word;

    static constexpr u8 bits_per_word = BITS<Word>;


    constexpr usize size() const { return N; }

    constexpr usize words() const { return m_data.size(); }

    constexpr Word word(usize i) const {
        gf2_debug_assert(i < words(), "Index {} is too large for a bitset with {} words.", i, words());
        return m_data[i];
    }

    constexpr void set_word(usize i, Word word) {
        gf2_debug_assert(i < words(), "Index {} is too large for a bitset with {} words.", i, words());
 
        // Set the value and if it's the last word, make sure it is kept clean
        m_data[i] = word;
        if (i == words() - 1) clean();
    }

    constexpr const Word* data() const { return m_data.data(); }

    constexpr Word* data() { return m_data.data(); }

    constexpr u8 offset() const { return 0; }


    constexpr void clean() {
        // NOTE: This works fine even if `size() == 0`.
        auto shift = N % bits_per_word;
        if (shift != 0) m_data[words() - 1] &= Word(~(MAX<Word> << shift));
    }

};
 
} // namespace gf2
 
// --------------------------------------------------------------------------------------------------------------------
// Specialises `std::formatter` for `BitSet` -- defers to the version for `BitStore` ...
// -------------------------------------------------------------------------------------------------------------------
template<gf2::usize N, gf2::unsigned_word Word>
struct std::formatter<gf2::BitSet<N, Word>> : std::formatter<gf2::BitStore<gf2::BitSet<N, Word>>> {
    // Inherits all functionality from `BitStore` formatter
};