HashTableCore.H

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/*---------------------------------------------------------------------------*\
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    Copyright (C) 2017-2025 OpenCFD Ltd.
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License
    This file is part of OpenFOAM.

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Class
    Foam::HashTableCore

Description
    Template invariant parts of hash table implementation.

SourceFiles
    HashTableCore.C

\*---------------------------------------------------------------------------*/

#ifndef Foam_HashTableCore_H
#define Foam_HashTableCore_H

#include "label.H"
#include "className.H"
#include "nullObject.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

namespace Foam
{

/*---------------------------------------------------------------------------*\
                        Class HashTableCore Declaration
\*---------------------------------------------------------------------------*/

//- Bits that are independent of HashTable template parameters.
struct HashTableCore
{
    //- Maximum allowable internal table size (must be a power of two!).
    // - approximately (INT32_MAX/4) => 0x20000000
    // - don't need an int64 version
    static constexpr int32_t maxTableSize = (1 << (32-3));

    //- Return a canonical (power-of-two) of the requested size.
    static label canonicalSize(const label size) noexcept;

    //- Declare type-name (with debug switch)
    ClassName("HashTable");

    //- Default construct
    constexpr HashTableCore() noexcept = default;

    static_assert
    (
        sizeof(NullObject) >= sizeof(void*),
        "NullObject is too small to reinterpret_cast as HashTable::iterator"
    );


    //- Factory class for creating a begin/end pair for any const iterator
    //- type, normally associated with a HashTable.
    //  Uses begin iterator and size for bookkeeping.
    template<class IteratorType, class TableType>
    class const_iterator_pair
    {
        const label size_;
        IteratorType iter_;

    public:

        //- Default construct an empty pair
        const_iterator_pair()
        :
            size_(0),
            iter_()
        {}

        //- Construct begin/end pair for table
        const_iterator_pair(const TableType& tbl)
        :
            size_(tbl.size()),
            iter_(tbl.begin())
        {}

        bool empty() const noexcept { return !size_; }
        label size() const noexcept { return size_; }

        IteratorType begin() const noexcept { return iter_; }
        IteratorType cbegin() const noexcept { return iter_; }

        IteratorType end() const { return IteratorType(); }
        IteratorType cend() const { return IteratorType(); }
    };
};


// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

} // End namespace Foam

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#endif

// ************************************************************************* //