boost/boost/geometry/policies/robustness/segment_ratio.hpp

// Boost.Geometry (aka GGL, Generic Geometry Library)

// Copyright (c) 2013 Barend Gehrels, Amsterdam, the Netherlands.

// Use, modification and distribution is subject to the Boost Software License,
// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)

#ifndef BOOST_GEOMETRY_POLICIES_ROBUSTNESS_SEGMENT_RATIO_HPP
#define BOOST_GEOMETRY_POLICIES_ROBUSTNESS_SEGMENT_RATIO_HPP

#include <boost/assert.hpp>
#include <boost/config.hpp>
#include <boost/rational.hpp>

#include <boost/geometry/util/math.hpp>
#include <boost/geometry/util/promote_floating_point.hpp>

namespace boost { namespace geometry
{


namespace detail { namespace segment_ratio
{

template
<
    typename Type,
    bool IsIntegral = boost::is_integral<Type>::type::value
>
struct less {};

template <typename Type>
struct less<Type, true>
{
    template <typename Ratio>
    static inline bool apply(Ratio const& lhs, Ratio const& rhs)
    {
        return boost::rational<Type>(lhs.numerator(), lhs.denominator())
             < boost::rational<Type>(rhs.numerator(), rhs.denominator());
    }
};

template <typename Type>
struct less<Type, false>
{
    template <typename Ratio>
    static inline bool apply(Ratio const& lhs, Ratio const& rhs)
    {
        BOOST_ASSERT(lhs.denominator() != 0);
        BOOST_ASSERT(rhs.denominator() != 0);
        return lhs.numerator() * rhs.denominator()
             < rhs.numerator() * lhs.denominator();
    }
};

template
<
    typename Type,
    bool IsIntegral = boost::is_integral<Type>::type::value
>
struct equal {};

template <typename Type>
struct equal<Type, true>
{
    template <typename Ratio>
    static inline bool apply(Ratio const& lhs, Ratio const& rhs)
    {
        return boost::rational<Type>(lhs.numerator(), lhs.denominator())
            == boost::rational<Type>(rhs.numerator(), rhs.denominator());
    }
};

template <typename Type>
struct equal<Type, false>
{
    template <typename Ratio>
    static inline bool apply(Ratio const& lhs, Ratio const& rhs)
    {
        BOOST_ASSERT(lhs.denominator() != 0);
        BOOST_ASSERT(rhs.denominator() != 0);
        return geometry::math::equals
            (
                lhs.numerator() * rhs.denominator(),
                rhs.numerator() * lhs.denominator()
            );
    }
};

}}

//! Small class to keep a ratio (e.g. 1/4)
//! Main purpose is intersections and checking on 0, 1, and smaller/larger
//! The prototype used Boost.Rational. However, we also want to store FP ratios,
//! (so numerator/denominator both in float)
//! and Boost.Rational starts with GCD which we prefer to avoid if not necessary
//! On a segment means: this ratio is between 0 and 1 (both inclusive)
//!
template <typename Type>
class segment_ratio
{
public :
    typedef Type numeric_type;

    // Type-alias for the type itself
    typedef segment_ratio<Type> thistype;

    inline segment_ratio()
        : m_numerator(0)
        , m_denominator(1)
        , m_approximation(0)
    {}

    inline segment_ratio(const Type& nominator, const Type& denominator)
        : m_numerator(nominator)
        , m_denominator(denominator)
    {
        initialize();
    }

    inline Type const& numerator() const { return m_numerator; }
    inline Type const& denominator() const { return m_denominator; }

    inline void assign(const Type& nominator, const Type& denominator)
    {
        m_numerator = nominator;
        m_denominator = denominator;
        initialize();
    }

    inline void initialize()
    {
        // Minimal normalization
        // 1/-4 => -1/4, -1/-4 => 1/4
        if (m_denominator < 0)
        {
            m_numerator = -m_numerator;
            m_denominator = -m_denominator;
        }

        typedef typename promote_floating_point<Type>::type num_type;
        static const num_type scale = 1000000.0;
        m_approximation =
            m_denominator == 0 ? 0
            : boost::numeric_cast<double>
                (
                    boost::numeric_cast<num_type>(m_numerator) * scale
                  / boost::numeric_cast<num_type>(m_denominator)
                );
    }

    inline bool is_zero() const { return math::equals(m_numerator, 0); }
    inline bool is_one() const { return math::equals(m_numerator, m_denominator); }
    inline bool on_segment() const
    {
        // e.g. 0/4 or 4/4 or 2/4
        return m_numerator >= 0 && m_numerator <= m_denominator;
    }
    inline bool in_segment() const
    {
        // e.g. 1/4
        return m_numerator > 0 && m_numerator < m_denominator;
    }
    inline bool on_end() const
    {
        // e.g. 0/4 or 4/4
        return is_zero() || is_one();
    }
    inline bool left() const
    {
        // e.g. -1/4
        return m_numerator < 0;
    }
    inline bool right() const
    {
        // e.g. 5/4
        return m_numerator > m_denominator;
    }

    inline bool close_to(thistype const& other) const
    {
        return geometry::math::abs(m_approximation - other.m_approximation) < 2;
    }

    inline bool operator< (thistype const& other) const
    {
        return close_to(other)
            ? detail::segment_ratio::less<Type>::apply(*this, other)
            : m_approximation < other.m_approximation;
    }

    inline bool operator== (thistype const& other) const
    {
        return close_to(other)
            && detail::segment_ratio::equal<Type>::apply(*this, other);
    }

    static inline thistype zero()
    {
        static thistype result(0, 1);
        return result;
    }

    static inline thistype one()
    {
        static thistype result(1, 1);
        return result;
    }

#if defined(BOOST_GEOMETRY_DEFINE_STREAM_OPERATOR_SEGMENT_RATIO)
    friend std::ostream& operator<<(std::ostream &os, segment_ratio const& ratio)
    {
        os << ratio.m_numerator << "/" << ratio.m_denominator
           << " (" << (static_cast<double>(ratio.m_numerator)
                        / static_cast<double>(ratio.m_denominator))
           << ")";
        return os;
    }
#endif



private :
    Type m_numerator;
    Type m_denominator;

    // Contains ratio on scale 0..1000000 (for 0..1)
    // This is an approximation for fast and rough comparisons
    // Boost.Rational is used if the approximations are close.
    // Reason: performance, Boost.Rational does a GCD by default and also the
    // comparisons contain while-loops.
    double m_approximation;
};


}} // namespace boost::geometry

#endif // BOOST_GEOMETRY_POLICIES_ROBUSTNESS_SEGMENT_RATIO_HPP