partition.h

#ifndef PARTITION_H
#define PARTITION_H

namespace bf {

template <typename Derived>
class partition_policy
{
public:
    unsigned parts() const
    {
        return derived().parts();
    }

private:
    //
    // CRTP interface
    //
    Derived& derived()
    {
        return *static_cast<Derived*>(this);
    }

    const Derived& derived() const
    {
        return *static_cast<const Derived*>(this);
    }
};

class no_partitioning : public partition_policy<no_partitioning>
{
public:
    no_partitioning(unsigned /* unused */)
    {
    }

    unsigned parts() const
    {
        return 1;
    }

    unsigned position(std::size_t hash, unsigned i, unsigned cells) const
    {
        return hash % cells;
    }
};

struct partitioning : public partition_policy<partitioning>
{
public:
    partitioning(unsigned parts)
      : parts_(parts)
    {
    }

    unsigned parts() const
    {
        return parts_;
    }

    unsigned position(std::size_t hash, unsigned i, unsigned cells) const
    {
        assert(cells % parts_ == 0);

        auto part_size = cells / parts_;
        return hash % part_size + (i * part_size);
    }

private:
    unsigned parts_;
};

} // namespace partition

#endif