FixedPointNumber implementation

DataStructures/FixedPointNumber.h

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+/*
+
+Copyright (c) 2013, Project OSRM, Dennis Luxen, others
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+Redistributions of source code must retain the above copyright notice, this list
+of conditions and the following disclaimer.
+Redistributions in binary form must reproduce the above copyright notice, this
+list of conditions and the following disclaimer in the documentation and/or
+other materials provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+*/
+
+#ifndef OSRM_FIXED_POINT_NUMBER_H
+#define OSRM_FIXED_POINT_NUMBER_H
+
+#include <cmath>
+#include <cstdint>
+
+#include <iostream>
+#include <limits>
+#include <type_traits>
+#include <utility>
+
+namespace osrm
+{
+
+// implements an binary based fixed point number type
+template <unsigned FractionalBitSize, bool is_unsigned = false, bool truncate_results = false>
+class FixedPointNumber
+{
+    static_assert(FractionalBitSize > 0, "FractionalBitSize must be greater than 0");
+    static_assert(FractionalBitSize <= 32, "FractionalBitSize must at most 32");
+
+    constexpr static const int32_t PRECISION = 1 << FractionalBitSize;
+
+    int32_t m_fixed_point_state;
+
+    // state signage encapsulates whether the state should either represent a
+    // signed or an unsigned floating point number
+    using state_signage =
+        typename std::conditional<is_unsigned,
+                                  std::make_unsigned<decltype(m_fixed_point_state)>::type,
+                                  decltype(m_fixed_point_state)>::type;
+
+  public:
+    FixedPointNumber() : m_fixed_point_state(0) {}
+
+    // the type is either initialized with a floating point value or an
+    // integral state. Anything else will throw at compile-time.
+    template <class T> FixedPointNumber(const T &&input) noexcept
+    {
+        static_assert(
+            std::is_floating_point<T>::value || std::is_integral<T>::value,
+            "FixedPointNumber needs to be initialized with floating point or integral value");
+        m_fixed_point_state =
+            static_cast<int32_t>(std::round(std::forward<const T>(input) * PRECISION));
+    }
+
+    // get max value
+    template <typename T,
+              typename std::enable_if<std::is_floating_point<T>::value>::type * = nullptr>
+    constexpr static auto max() noexcept -> T
+    {
+        return static_cast<T>(std::numeric_limits<state_signage>::max()) / PRECISION;
+    }
+
+    // get min value
+    template <typename T,
+              typename std::enable_if<std::is_floating_point<T>::value>::type * = nullptr>
+    constexpr static auto min() noexcept -> T
+    {
+        return static_cast<T>(1) / PRECISION;
+    }
+
+    // get lowest value
+    template <typename T,
+              typename std::enable_if<std::is_floating_point<T>::value>::type * = nullptr>
+    constexpr static auto lowest() noexcept -> T
+    {
+        return static_cast<T>(std::numeric_limits<state_signage>::min()) / PRECISION;
+    }
+
+    // cast to floating point type T, return value
+    template <typename T,
+              typename std::enable_if<std::is_floating_point<T>::value>::type * = nullptr>
+    operator T() const noexcept
+    {
+        // casts to external type (signed or unsigned) and then to float
+        return static_cast<T>(static_cast<state_signage>(m_fixed_point_state)) / PRECISION;
+    }
+
+    // warn about cast to integral type T, its disabled for good reason
+    template <typename T, typename std::enable_if<std::is_integral<T>::value>::type * = nullptr>
+    operator T() const
+    {
+        static_assert(std::is_integral<T>::value,
+                      "casts to integral types have been disabled on purpose");
+    }
+
+    // compare, ie. sort fixed-point numbers
+    void operator<(const FixedPointNumber &other) const noexcept
+    {
+        return m_fixed_point_state < other.m_fixed_point_state;
+    }
+
+    // arithmetic operators
+    FixedPointNumber operator+(const FixedPointNumber &other) const noexcept
+    {
+        FixedPointNumber tmp = *this;
+        tmp.m_fixed_point_state += other.m_fixed_point_state;
+        return tmp;
+    }
+
+    FixedPointNumber &operator+=(const FixedPointNumber &other) noexcept
+    {
+        this->m_fixed_point_state += other.m_fixed_point_state;
+        return *this;
+    }
+
+    FixedPointNumber operator-(const FixedPointNumber &other) const noexcept
+    {
+        FixedPointNumber tmp = *this;
+        tmp.m_fixed_point_state -= other.m_fixed_point_state;
+        return tmp;
+    }
+
+    FixedPointNumber &operator-=(const FixedPointNumber &other) noexcept
+    {
+        this->m_fixed_point_state -= other.m_fixed_point_state;
+        return *this;
+    }
+
+    FixedPointNumber operator*(const FixedPointNumber &other) const noexcept
+    {
+        int64_t temp = this->m_fixed_point_state;
+        temp *= other.m_fixed_point_state;
+
+        // rounding!
+        if (!truncate_results)
+        {
+            temp = temp + ((temp & 1 << (FractionalBitSize - 1)) << 1);
+        }
+        temp >>= FractionalBitSize;
+        FixedPointNumber tmp;
+        tmp.m_fixed_point_state = static_cast<int32_t>(temp);
+        return tmp;
+    }
+
+    FixedPointNumber &operator*=(const FixedPointNumber &other) noexcept
+    {
+        int64_t temp = this->m_fixed_point_state;
+        temp *= other.m_fixed_point_state;
+
+        // rounding!
+        temp = temp + ((temp & 1 << (FractionalBitSize - 1)) << 1);
+        temp >>= FractionalBitSize;
+        this->m_fixed_point_state = static_cast<int32_t>(temp);
+        return *this;
+    }
+
+    FixedPointNumber operator/(const FixedPointNumber &other) const noexcept
+    {
+        int64_t temp = this->m_fixed_point_state;
+        temp <<= FractionalBitSize;
+        temp /= static_cast<int64_t>(other.m_fixed_point_state);
+        FixedPointNumber tmp;
+        tmp.m_fixed_point_state = static_cast<int32_t>(temp);
+        return tmp;
+    }
+
+    FixedPointNumber &operator/=(const FixedPointNumber &other) noexcept
+    {
+        int64_t temp = this->m_fixed_point_state;
+        temp <<= FractionalBitSize;
+        temp /= static_cast<int64_t>(other.m_fixed_point_state);
+        FixedPointNumber tmp;
+        this->m_fixed_point_state = static_cast<int32_t>(temp);
+        return *this;
+    }
+};
+
+static_assert(4 == sizeof(FixedPointNumber<1>), "FP19 has wrong size != 4");
+}
+#endif // OSRM_FIXED_POINT_NUMBER_H