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