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110 lines
3.1 KiB
C++
110 lines
3.1 KiB
C++
///////////////////////////////////////////////////////////////
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// Copyright 2021 John Maddock. Distributed under the Boost
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// Software License, Version 1.0. (See accompanying file
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// LICENSE_1_0.txt or copy at https://www.boost.org/LICENSE_1_0.txt
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//
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// Simple test that cpp_int -> double conversion has less than 0.5ulp error
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// and rounds to even in case of ties.
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// See https://github.com/boostorg/multiprecision/issues/360.
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//
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#ifdef _MSC_VER
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#define _SCL_SECURE_NO_WARNINGS
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#endif
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#include <boost/multiprecision/cpp_int.hpp>
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#include <boost/random/mersenne_twister.hpp>
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#include <boost/random/uniform_int.hpp>
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#include "test.hpp"
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using namespace boost::multiprecision;
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#ifdef BOOST_MSVC
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#pragma warning(disable : 4127)
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#endif
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template <class T>
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T generate_random(unsigned bits_wanted)
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{
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static boost::random::mt19937 gen;
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typedef boost::random::mt19937::result_type random_type;
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T max_val;
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unsigned digits;
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if (std::numeric_limits<T>::is_bounded && (bits_wanted == (unsigned)std::numeric_limits<T>::digits))
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{
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max_val = (std::numeric_limits<T>::max)();
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digits = std::numeric_limits<T>::digits;
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}
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else
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{
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max_val = T(1) << bits_wanted;
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digits = bits_wanted;
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}
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unsigned bits_per_r_val = std::numeric_limits<random_type>::digits - 1;
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while ((random_type(1) << bits_per_r_val) > (gen.max)())
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--bits_per_r_val;
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unsigned terms_needed = digits / bits_per_r_val + 1;
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T val = 0;
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for (unsigned i = 0; i < terms_needed; ++i)
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{
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val *= (gen.max)();
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val += gen();
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}
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val %= max_val;
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return val;
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}
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template <class From, class To>
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void test_convert()
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{
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boost::random::mt19937 gen;
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boost::random::uniform_int_distribution<> d(20, (std::min)(200, std::numeric_limits<To>::max_exponent - 2));
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for (unsigned i = 0; i < 10000; ++i)
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{
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int bits = d(gen);
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From from = generate_random<From>(bits);
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To t1(from);
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From b(t1);
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std::size_t m = msb(from);
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if (m >= std::numeric_limits<To>::digits)
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{
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// For error <= 1ulp
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// Note msb(from) returns one less than the number of bits in from:
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From max_error = (From(1) << (m - std::numeric_limits<To>::digits));
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BOOST_TEST_GE(max_error, abs(b - from));
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if (max_error < abs(b - from))
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// debugging help:
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std::cout << from << std::endl
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<< b << std::endl
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<< abs(b - from) << std::endl;
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if (max_error == abs(b - from))
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{
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// Check we rounded to even in case of tie:
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BOOST_TEST_GT(lsb(b), (1 + msb(from) - std::numeric_limits<To>::digits));
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if (lsb(b) <= (1 + msb(from) - std::numeric_limits<To>::digits))
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{
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// debugging help:
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std::cout << from << std::endl
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<< b << std::endl
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<< abs(b - from) << std::endl;
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}
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}
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}
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else
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{
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BOOST_TEST_EQ(b, from);
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}
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}
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}
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int main()
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{
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test_convert<cpp_int, float>();
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test_convert<cpp_int, double>();
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return boost::report_errors();
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}
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