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281 lines
8 KiB
C++
281 lines
8 KiB
C++
#ifndef BOOST_NUMERIC_UTILITY_HPP
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#define BOOST_NUMERIC_UTILITY_HPP
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// Copyright (c) 2015 Robert Ramey
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#include <cstdint> // intmax_t, uintmax_t, uint8_t, ...
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#include <algorithm>
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#include <type_traits> // conditional
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#include <limits>
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#include <cassert>
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#include <utility> // pair
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#include <boost/integer.hpp> // (u)int_t<>::least, exact
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namespace boost {
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namespace safe_numerics {
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namespace utility {
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///////////////////////////////////////////////////////////////////////////////
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// used for debugging
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// provokes warning message with names of type T
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// usage - print_types<T, ...>;
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// see https://cukic.co/2019/02/19/tmp-testing-and-debugging-templates
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/*
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template<typename Tx>
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using print_type = typename Tx::error_message;
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*/
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template <typename... Ts>
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struct [[deprecated]] print_types {};
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// display value of constexpr during compilation
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// usage print_value(N) pn;
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template<int N>
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struct print_value
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{
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enum test : char {
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value = N < 0 ? N - 256 : N + 256
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};
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};
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#if 0
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// static warning - same as static_assert but doesn't
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// stop compilation.
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template <typename T>
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struct static_test{};
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template <>
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struct static_test<std::false_type>{
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[[deprecated]] static_test(){}
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};
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template<typename T>
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constexpr void static_warning(const T){
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//using x = static_test<T>;
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const static_test<T> x;
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}
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#endif
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/*
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// can be called by constexpr to produce a compile time
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// trap of parameter passed is false.
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// usage constexpr_assert(bool)
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constexpr int constexpr_assert(const bool tf){
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return 1 / tf;
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}
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*/
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///////////////////////////////////////////////////////////////////////////////
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// return an integral constant equal to the the number of bits
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// held by some integer type (including the sign bit)
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template<typename T>
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using bits_type = std::integral_constant<
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int,
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std::numeric_limits<T>::digits
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+ (std::numeric_limits<T>::is_signed ? 1 : 0)
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>;
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/*
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From http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogObvious
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Find the log base 2 of an integer with a lookup table
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static const char LogTable256[256] =
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{
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#define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n
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-1, 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
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LT(4), LT(5), LT(5), LT(6), LT(6), LT(6), LT(6),
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LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7)
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};
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unsigned int v; // 32-bit word to find the log of
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unsigned r; // r will be lg(v)
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register unsigned int t, tt; // temporaries
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if (tt = v >> 16)
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{
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r = (t = tt >> 8) ? 24 + LogTable256[t] : 16 + LogTable256[tt];
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}
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else
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{
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r = (t = v >> 8) ? 8 + LogTable256[t] : LogTable256[v];
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}
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The lookup table method takes only about 7 operations to find the log of a 32-bit value.
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If extended for 64-bit quantities, it would take roughly 9 operations. Another operation
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can be trimmed off by using four tables, with the possible additions incorporated into each.
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Using int table elements may be faster, depending on your architecture.
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*/
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namespace ilog2_detail {
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// I've "improved" the above and recast as C++ code which depends upon
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// the optimizer to minimize the operations. This should result in
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// nine operations to calculate the position of the highest order
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// bit in a 64 bit number. RR
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constexpr static unsigned int ilog2(const boost::uint_t<8>::exact & t){
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#define LT(n) n, n, n, n, n, n, n, n, n, n, n, n, n, n, n, n
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const char LogTable256[256] = {
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static_cast<const char>(-1), 0, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3,
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LT(4), LT(5), LT(5), LT(6), LT(6), LT(6), LT(6),
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LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7), LT(7)
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};
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return LogTable256[t];
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}
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constexpr static unsigned int ilog2(const boost::uint_t<16>::exact & t){
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const boost::uint_t<8>::exact upper_half = (t >> 8);
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return upper_half == 0
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? ilog2(static_cast<boost::uint_t<8>::exact>(t))
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: 8 + ilog2(upper_half);
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}
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constexpr static unsigned int ilog2(const boost::uint_t<32>::exact & t){
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const boost::uint_t<16>::exact upper_half = (t >> 16);
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return upper_half == 0
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? ilog2(static_cast<boost::uint_t<16>::exact>(t))
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: 16 + ilog2(upper_half);
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}
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constexpr static unsigned int ilog2(const boost::uint_t<64>::exact & t){
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const boost::uint_t<32>::exact upper_half = (t >> 32);
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return upper_half == 0
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? ilog2(static_cast<boost::uint_t<32>::exact>(t))
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: 32 + ilog2(upper_half);
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}
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} // ilog2_detail
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template<typename T>
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constexpr unsigned int ilog2(const T & t){
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// log not defined for negative numbers
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// assert(t > 0);
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if(t == 0)
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return 0;
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return ilog2_detail::ilog2(
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static_cast<
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typename boost::uint_t<
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bits_type<T>::value
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>::least
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>(t)
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);
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}
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// the number of bits required to render the value in x
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// including sign bit
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template<typename T>
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constexpr unsigned int significant_bits(const T & t){
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return 1 + ((t < 0) ? ilog2(~t) : ilog2(t));
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}
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/*
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// give the value t, return the number which corresponds
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// to all 1's which is higher than that number
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template<typename T>
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constexpr unsigned int bits_value(const T & t){
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const unsigned int sb = significant_bits(t);
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const unsigned int sb_max = significant_bits(std::numeric_limits<T>::max());
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return sb < sb_max ? ((sb << 1) - 1) : std::numeric_limits<T>::max();
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}
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*/
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///////////////////////////////////////////////////////////////////////////////
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// meta functions returning types
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// If we use std::max in here we get internal compiler errors
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// with MSVC (tested VC2017) ...
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// Notes from https://en.cppreference.com/w/cpp/algorithm/max
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// Capturing the result of std::max by reference if one of the parameters
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// is rvalue produces a dangling reference if that parameter is returned.
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template <class T>
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// turns out this problem crashes all versions of gcc compilers. So
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// make sure we return by value
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//constexpr const T & max(
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constexpr T max(
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const T & lhs,
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const T & rhs
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){
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return lhs > rhs ? lhs : rhs;
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}
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// given a signed range, return type required to hold all the values
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// in the range
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template<
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std::intmax_t Min,
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std::intmax_t Max
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>
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using signed_stored_type = typename boost::int_t<
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max(
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significant_bits(Min),
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significant_bits(Max)
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) + 1
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>::least ;
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// given an unsigned range, return type required to hold all the values
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// in the range
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template<
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std::uintmax_t Min,
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std::uintmax_t Max
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>
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// unsigned range
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using unsigned_stored_type = typename boost::uint_t<
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significant_bits(Max)
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>::least;
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///////////////////////////////////////////////////////////////////////////////
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// constexpr functions
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// need our own version because official version
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// a) is not constexpr
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// b) is not guarenteed to handle non-assignable types
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template<typename T>
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constexpr std::pair<T, T>
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minmax(const std::initializer_list<T> l){
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assert(l.size() > 0);
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const T * minimum = l.begin();
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const T * maximum = l.begin();
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for(const T * i = l.begin(); i != l.end(); ++i){
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if(*i < * minimum)
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minimum = i;
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else
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if(* maximum < *i)
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maximum = i;
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}
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return std::pair<T, T>{* minimum, * maximum};
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}
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// for any given t
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// a) figure number of significant bits
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// b) return a value with all significant bits set
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// so for example:
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// 3 == round_out(2) because
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// 2 == 10 and 3 == 11
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template<typename T>
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constexpr T round_out(const T & t){
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if(t >= 0){
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const std::uint8_t sb = utility::significant_bits(t);
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return (sb < sizeof(T) * 8)
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? ((T)1 << sb) - 1
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: std::numeric_limits<T>::max();
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}
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else{
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const std::uint8_t sb = utility::significant_bits(~t);
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return (sb < sizeof(T) * 8)
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? ~(((T)1 << sb) - 1)
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: std::numeric_limits<T>::min();
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}
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}
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} // utility
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} // safe_numerics
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} // boost
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#endif // BOOST_NUMERIC_UTILITY_HPP
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