dlib C++ Library - projection_hash.h

    // Copyright (C) 2011  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #ifndef DLIB_PROJECTION_HASh_Hh_
    #define DLIB_PROJECTION_HASh_Hh_

    #include "projection_hash_abstract.h"
    #include "../matrix.h"
    #include "../rand.h"
    #include <vector>

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        class projection_hash
        {
        public:

            projection_hash() {}

            template <typename EXP1, typename EXP2>
            projection_hash(
                const matrix_exp<EXP1>& proj_,
                const matrix_exp<EXP2>& offset_
            ) : proj(proj_), offset(offset_)
            {
                // make sure requires clause is not broken
                DLIB_ASSERT(proj.nr() == offset.nr(),
                    "\t projection_hash::projection_hash()"
                    << "\n\t Invalid arguments were given to this function."
                    << "\n\t proj.nr():   " << proj.nr()
                    << "\n\t offset.nr(): " << offset.nr()
                    );

            }

            const matrix<double>& get_projection_matrix (
            ) const { return proj; }

            const matrix<double,0,1>& get_offset_matrix (
            ) const { return offset; }

            unsigned long num_hash_bins (
            ) const
            {
                return static_cast<unsigned long>(std::pow(2.0, (double)offset.size()));
            }

            template <typename EXP>
            unsigned long operator() (
                const matrix_exp<EXP>& v
            ) const
            {
                // make sure requires clause is not broken
                DLIB_ASSERT(is_col_vector(v) &&
                            v.size() == get_projection_matrix().nc() &&
                            v.size() > 0,
                    "\t unsigned long projection_hash::operator()(v)"
                    << "\n\t Invalid arguments were given to this function."
                    << "\n\t is_col_vector(v):             " << is_col_vector(v)
                    << "\n\t get_projection_matrix().nc(): " << get_projection_matrix().nc()
                    << "\n\t v.size():                     " << v.size()
                    );

                return do_hash(proj*matrix_cast<double>(v) + offset);
            }

        private:

            template <typename EXP>
            unsigned long do_hash (
                const matrix_exp<EXP>& v
            ) const
            {
                unsigned long h = 0;
                for (long i = 0; i < v.size(); ++i)
                {
                    h <<= 1;
                    if (v(i) > 0)
                        h |= 1;
                }
                return h;
            }

            matrix<double> proj;
            matrix<double,0,1> offset;
        };

    // ----------------------------------------------------------------------------------------

        inline void serialize (
            const projection_hash& item,
            std::ostream& out
        )
        {
            serialize(item.get_projection_matrix(), out);
            serialize(item.get_offset_matrix(), out);
        }

        inline void deserialize (
            projection_hash& item,
            std::istream& in
        )
        {
            matrix<double> proj;
            matrix<double,0,1> offset;
            deserialize(proj, in);
            deserialize(offset, in);
            item = projection_hash(proj, offset);
        }

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_PROJECTION_HASh_Hh_