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// Copyright Catch2 Authors
// Distributed under the Boost Software License, Version 1.0.
// (See accompanying file LICENSE.txt or copy at
// https://www.boost.org/LICENSE_1_0.txt)
// SPDX-License-Identifier: BSL-1.0
#ifndef CATCH_RANDOM_FLOATING_POINT_HELPERS_HPP_INCLUDED
#define CATCH_RANDOM_FLOATING_POINT_HELPERS_HPP_INCLUDED
#include <catch2/internal/catch_polyfills.hpp>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <limits>
#include <type_traits>
namespace Catch {
namespace Detail {
/**
* Returns the largest magnitude of 1-ULP distance inside the [a, b] range.
*
* Assumes `a < b`.
*/
template <typename FloatType>
FloatType gamma(FloatType a, FloatType b) {
static_assert( std::is_floating_point<FloatType>::value,
"gamma returns the largest ULP magnitude within "
"floating point range [a, b]. This only makes sense "
"for floating point types" );
assert( a <= b );
const auto gamma_up = Catch::nextafter( a, std::numeric_limits<FloatType>::infinity() ) - a;
const auto gamma_down = b - Catch::nextafter( b, -std::numeric_limits<FloatType>::infinity() );
return gamma_up < gamma_down ? gamma_down : gamma_up;
}
template <typename FloatingPoint>
struct DistanceTypePicker;
template <>
struct DistanceTypePicker<float> {
using type = std::uint32_t;
};
template <>
struct DistanceTypePicker<double> {
using type = std::uint64_t;
};
template <typename T>
using DistanceType = typename DistanceTypePicker<T>::type;
#if defined( __GNUC__ ) || defined( __clang__ )
# pragma GCC diagnostic push
# pragma GCC diagnostic ignored "-Wfloat-equal"
#endif
/**
* Computes the number of equi-distant floats in [a, b]
*
* Since not every range can be split into equidistant floats
* exactly, we actually compute ceil(b/distance - a/distance),
* because in those cases we want to overcount.
*
* Uses modified Dekker's FastTwoSum algorithm to handle rounding.
*/
template <typename FloatType>
DistanceType<FloatType>
count_equidistant_floats( FloatType a, FloatType b, FloatType distance ) {
assert( a <= b );
// We get distance as gamma for our uniform float distribution,
// so this will round perfectly.
const auto ag = a / distance;
const auto bg = b / distance;
const auto s = bg - ag;
const auto err = ( std::fabs( a ) <= std::fabs( b ) )
? -ag - ( s - bg )
: bg - ( s + ag );
const auto ceil_s = static_cast<DistanceType<FloatType>>( std::ceil( s ) );
return ( ceil_s != s ) ? ceil_s : ceil_s + ( err > 0 );
}
#if defined( __GNUC__ ) || defined( __clang__ )
# pragma GCC diagnostic pop
#endif
}
} // end namespace Catch
#endif // CATCH_RANDOM_FLOATING_POINT_HELPERS_HPP_INCLUDED
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