576 lines
16 KiB
C++
576 lines
16 KiB
C++
/*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*
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* Copyright 2010-2014 Danny Robson <danny@nerdcruft.net>
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*/
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#ifndef __MATHS_HPP
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#define __MATHS_HPP
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#include "./debug.hpp"
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#include "./types/traits.hpp"
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#include "./float.hpp"
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#include <cmath>
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#include <cstdint>
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#include <limits>
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#include <type_traits>
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#include <utility>
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///////////////////////////////////////////////////////////////////////////////
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// NOTE: You may be tempted to add all sorts of performance enhancing
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// attributes (like gnu::const or gnu::pure). DO NOT DO THIS WITHOUT EXTENSIVE
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// TESTING. Just about everything will break in some way with these attributes.
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//
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// In particular: it is safest to apply these only to leaf functions
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///////////////////////////////////////////////////////////////////////////////
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namespace util {
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template <typename T>
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T
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abs [[gnu::const]] (T t)
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{
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return t > 0 ? t : -t;
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}
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///////////////////////////////////////////////////////////////////////////
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// exponentials
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template <typename T>
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constexpr T
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pow2 [[gnu::const]] (T value)
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{
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return value * value;
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}
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///////////////////////////////////////////////////////////////////////////
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template <typename T>
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constexpr T
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pow [[gnu::const]] (T x, unsigned y)
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{
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return y == 0 ? T{1} : x * pow (x, y - 1);
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}
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//-------------------------------------------------------------------------
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template <typename T>
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constexpr
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std::enable_if_t<std::is_integral<T>::value, bool>
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is_pow2 [[gnu::const]] (T value)
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{
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return value && !(value & (value - 1));
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}
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//-----------------------------------------------------------------------------
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// Logarithms
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template <typename T>
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T
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log2 (T val);
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//-------------------------------------------------------------------------
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template <typename T>
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T
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log2up (T val);
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///////////////////////////////////////////////////////////////////////////////
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// Rounding
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template <typename T, typename U>
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inline
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typename std::common_type<
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std::enable_if_t<std::is_integral<T>::value,T>,
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std::enable_if_t<std::is_integral<U>::value,U>
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>::type
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round_to (T value, U size)
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{
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if (value % size == 0)
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return value;
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return value + (size - value % size);
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}
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//-----------------------------------------------------------------------------
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template <typename T>
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std::enable_if_t<
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std::is_integral<T>::value, T
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>
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round_pow2 (T value);
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//-----------------------------------------------------------------------------
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template <typename T, typename U>
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constexpr std::enable_if_t<
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std::is_integral<T>::value &&
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std::is_integral<U>::value,
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T
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>
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divup (const T a, const U b)
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{
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return (a + b - 1) / b;
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}
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///////////////////////////////////////////////////////////////////////////////
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// Properties
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template <typename T>
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bool
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is_integer (const T& value);
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//-----------------------------------------------------------------------------
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template <typename T>
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unsigned
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digits (const T& value);
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///----------------------------------------------------------------------------
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/// return positive or negative unit value corresponding to the input.
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template <typename T>
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constexpr std::enable_if_t<
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std::is_signed<T>::value && std::is_integral<T>::value, T
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>
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sign (T t)
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{
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return t < 0 ? -1 : 1;
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}
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///------------------------------------------------------------------------
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/// return positive or negative unit value corresponding to the input.
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/// guaranteed to give correct results for signed zeroes, use another
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/// method if extreme speed is important.
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template <typename T>
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constexpr std::enable_if_t<
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std::is_floating_point<T>::value, T
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>
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sign (T t)
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{
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return std::signbit (t) ? -1 : 1;
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}
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///////////////////////////////////////////////////////////////////////////////
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// factorisation
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template <typename T>
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constexpr T
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gcd (T a, T b)
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{
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if (a == b) return a;
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if (a > b) return gcd (a - b, b);
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if (b > a) return gcd (a, b - a);
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unreachable ();
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}
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///////////////////////////////////////////////////////////////////////////////
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// Comparisons
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inline bool
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almost_equal (const float &a, const float &b)
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{
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return ieee_single::almost_equal (a, b);
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}
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//-----------------------------------------------------------------------------
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inline bool
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almost_equal (const double &a, const double &b)
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{
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return ieee_double::almost_equal (a, b);
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}
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//-----------------------------------------------------------------------------
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template <typename A, typename B>
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typename std::enable_if_t<
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std::is_floating_point<A>::value &&
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std::is_floating_point<B>::value,
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bool
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>
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almost_equal (const A &a, const B &b)
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{
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using common_t = std::common_type_t<A,B>;
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return almost_equal<common_t> (static_cast<common_t> (a),
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static_cast<common_t> (b));
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}
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//-----------------------------------------------------------------------------
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template <typename A, typename B>
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typename std::enable_if_t<
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std::is_integral<A>::value &&
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std::is_integral<B>::value &&
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std::is_signed<A>::value == std::is_signed<B>::value,
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bool
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>
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almost_equal (const A &a, const B &b) {
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using common_t = std::common_type_t<A,B>;
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return static_cast<common_t> (a) == static_cast<common_t> (b);
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}
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//-----------------------------------------------------------------------------
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template <typename Ta, typename Tb>
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typename std::enable_if<
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!std::is_arithmetic<Ta>::value ||
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!std::is_arithmetic<Tb>::value,
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bool
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>::type
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almost_equal (const Ta &a, const Tb &b)
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{ return a == b; }
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//-----------------------------------------------------------------------------
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// Useful for explictly ignore equality warnings
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#pragma GCC diagnostic push
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#pragma GCC diagnostic ignored "-Wfloat-equal"
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template <typename T, typename U>
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bool
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exactly_equal (const T &a, const U &b)
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{ return a == b; }
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#pragma GCC diagnostic pop
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//-----------------------------------------------------------------------------
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template <typename T>
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bool
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almost_zero (T a)
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{ return almost_equal (a, T{0}); }
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//-----------------------------------------------------------------------------
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template <typename T>
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bool
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exactly_zero (T a)
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{ return exactly_equal (a, T{0}); }
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//-----------------------------------------------------------------------------
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template <typename T>
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const T&
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identity (const T& t)
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{
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return t;
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}
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///////////////////////////////////////////////////////////////////////////////
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// angles, trig
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template <typename T>
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constexpr T PI = T(3.141592653589793238462643);
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//-----------------------------------------------------------------------------
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template <typename T>
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constexpr T E = T(2.71828182845904523536028747135266250);
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//-----------------------------------------------------------------------------
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template <typename T>
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constexpr T
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to_degrees (T radians)
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{
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static_assert (std::is_floating_point<T>::value, "undefined for integral types");
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return radians * 180 / PI<T>;
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}
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//-----------------------------------------------------------------------------
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template <typename T>
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constexpr T
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to_radians (T degrees)
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{
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static_assert (std::is_floating_point<T>::value, "undefined for integral types");
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return degrees / 180 * PI<T>;
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}
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//-----------------------------------------------------------------------------
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//! Normalised sinc function
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template <typename T>
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constexpr T
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sincn (T x)
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{
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return almost_zero (x) ? 1 : std::sin (PI<T> * x) / (PI<T> * x);
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}
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//-----------------------------------------------------------------------------
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//! Unnormalised sinc function
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template <typename T>
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constexpr T
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sincu (T x)
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{
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return almost_zero (x) ? 1 : std::sin (x) / x;
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}
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///////////////////////////////////////////////////////////////////////////////
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// combinatorics
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constexpr uintmax_t
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factorial (unsigned i)
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{
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return i <= 1 ? 0 : i * factorial (i - 1);
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}
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//-----------------------------------------------------------------------------
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/// stirlings approximation of factorials
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constexpr uintmax_t
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stirling (unsigned n)
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{
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return static_cast<uintmax_t> (
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std::sqrt (2 * PI<float> * n) * std::pow (n / E<float>, n)
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);
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}
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//-----------------------------------------------------------------------------
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constexpr uintmax_t
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combination (unsigned n, unsigned k)
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{
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return factorial (n) / (factorial (k) / (factorial (n - k)));
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}
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///////////////////////////////////////////////////////////////////////////////
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// kahan summation for long floating point sequences
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template <class InputIt>
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typename std::iterator_traits<InputIt>::value_type
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fsum (InputIt first, InputIt last)
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{
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using T = typename std::iterator_traits<InputIt>::value_type;
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static_assert (std::is_floating_point<T>::value,
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"fsum only works for floating point types");
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T sum = 0;
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T c = 0;
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for (auto cursor = first; cursor != last; ++cursor) {
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T y = *cursor - c;
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T t = sum + y;
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c = (t - sum) - y;
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sum = t;
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}
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return sum;
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}
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///////////////////////////////////////////////////////////////////////////
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/// Variadic minimum
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template <typename T>
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constexpr T
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min (const T a)
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{ return a; }
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//-------------------------------------------------------------------------
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template <typename T, typename U, typename ...Args>
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constexpr std::enable_if_t<
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std::is_unsigned<std::decay_t<T>>::value == std::is_unsigned<std::decay_t<U>>::value &&
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std::is_integral<std::decay_t<T>>::value == std::is_integral<std::decay_t<U>>::value,
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std::common_type_t<T,U>
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>
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min (const T a, const U b, Args ...args)
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{
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return min (a < b ? a : b, std::forward<Args> (args)...);
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}
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//-------------------------------------------------------------------------
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/// Variadic maximum
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template <typename T>
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constexpr T
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max (const T a)
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{ return a; }
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//-------------------------------------------------------------------------
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template <typename T, typename U, typename ...Args>
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constexpr std::enable_if_t<
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std::is_unsigned<std::decay_t<T>>::value == std::is_unsigned<std::decay_t<U>>::value &&
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std::is_integral<std::decay_t<T>>::value == std::is_integral<std::decay_t<U>>::value,
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std::common_type_t<T,U>
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>
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max (const T a, const U b, Args ...args)
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{
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return max (a > b ? a : b, std::forward<Args> (args)...);
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}
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///////////////////////////////////////////////////////////////////////////
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// Limiting functions
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// min/max clamping
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template <typename T, typename U, typename V>
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constexpr T
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limit (const T val, const U lo, const V hi)
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{
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lo <= hi ? (void)0 : panic ();
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return val > hi ? hi:
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val < lo ? lo:
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val;
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}
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//-------------------------------------------------------------------------
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// clamped cubic hermite interpolation
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template <typename T>
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T
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smoothstep (T a, T b, T x)
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{
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CHECK_LE(a, b);
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x = limit ((x - a) / (b - a), T{0}, T{1});
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return x * x * (3 - 2 * x);
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}
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///////////////////////////////////////////////////////////////////////////
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// renormalisation of unit floating point and/or normalised integers
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// int -> float
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template <typename T, typename U>
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constexpr
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typename std::enable_if<
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!std::is_floating_point<T>::value && std::is_floating_point<U>::value, U
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>::type
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renormalise (T t)
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{
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return t / static_cast<U> (std::numeric_limits<T>::max ());
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}
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//-------------------------------------------------------------------------
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// float -> int
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template <typename T, typename U>
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constexpr
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typename std::enable_if<
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std::is_floating_point<T>::value && !std::is_floating_point<U>::value, U
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>::type
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renormalise (T t)
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{
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// Ideally std::ldexp would be involved but it complicates handing
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// integers with greater precision than our floating point type. Also it
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// would prohibit constexpr and involve errno.
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size_t usable = std::numeric_limits<T>::digits;
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size_t available = sizeof (U) * 8;
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size_t shift = std::max (available, usable) - usable;
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t = limit (t, 0, 1);
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// construct an integer of the float's mantissa size, multiply it by our
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// parameter, then shift it back into the full range of the integer type.
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U in = std::numeric_limits<U>::max () >> shift;
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U mid = static_cast<U> (t * in);
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U out = mid << shift;
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// use the top bits of the output to fill the bottom bits which through
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// shifting would otherwise be zero. this gives us the full extent of the
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// integer range, while varying predictably through the entire output
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// space.
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return out | out >> (available - shift);
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}
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//-------------------------------------------------------------------------
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// float -> float, avoid identity conversion as we don't want to create
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// ambiguous overloads
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template <typename T, typename U>
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constexpr
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typename std::enable_if<
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std::is_floating_point<T>::value &&
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std::is_floating_point<U>::value &&
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!std::is_same<T,U>::value, U
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>::type
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renormalise (T t)
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{
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return static_cast<U> (t);
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}
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//-------------------------------------------------------------------------
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// hi_int -> lo_int
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template <typename T, typename U>
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constexpr
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typename std::enable_if<
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std::is_integral<T>::value &&
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std::is_integral<U>::value &&
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(sizeof (T) > sizeof (U)), U
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>::type
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renormalise (T t)
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{
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static_assert (sizeof (T) > sizeof (U),
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"assumes right shift is sufficient");
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// we have excess bits ,just shift and return
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constexpr auto shift = 8 * (sizeof (T) - sizeof (U));
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return t >> shift;
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}
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//-------------------------------------------------------------------------
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// lo_int -> hi_int
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template <typename T, typename U>
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constexpr
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typename std::enable_if<
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std::is_integral<T>::value &&
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std::is_integral<U>::value &&
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sizeof (T) < sizeof (U), U
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>::type
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renormalise (T t)
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{
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static_assert (sizeof (T) < sizeof (U),
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"assumes bit creation is required to fill space");
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// we need to create bits. fill the output integer with copies of ourself.
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// this is approximately correct in the general case (introducing a small
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// linear positive bias), but allows us to fill the output space in the
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// case of input maximum.
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static_assert (sizeof (U) % sizeof (T) == 0,
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"assumes integer multiple of sizes");
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U out = 0;
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for (size_t i = 0; i < sizeof (U) / sizeof (T); ++i)
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out |= U (t) << sizeof (T) * 8 * i;
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return out;
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}
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//-------------------------------------------------------------------------
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template <typename T, typename U>
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constexpr
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typename std::enable_if<
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std::is_same<T,U>::value, U
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>::type
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renormalise (T t)
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{ return t; }
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}
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#endif // __MATHS_HPP
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