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// Copyright 2021 The Abseil Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef Y_ABSL_NUMERIC_INTERNAL_REPRESENTATION_H_
#define Y_ABSL_NUMERIC_INTERNAL_REPRESENTATION_H_
#include <limits>
#include "y_absl/base/config.h"
namespace y_absl {
Y_ABSL_NAMESPACE_BEGIN
namespace numeric_internal {
// Returns true iff long double is represented as a pair of doubles added
// together.
inline constexpr bool IsDoubleDouble() {
// A double-double value always has exactly twice the precision of a double
// value--one double carries the high digits and one double carries the low
// digits. This property is not shared with any other common floating-point
// representation, so this test won't trigger false positives. For reference,
// this table gives the number of bits of precision of each common
// floating-point representation:
//
// type precision
// IEEE single 24 b
// IEEE double 53
// x86 long double 64
// double-double 106
// IEEE quadruple 113
//
// Note in particular that a quadruple-precision float has greater precision
// than a double-double float despite taking up the same amount of memory; the
// quad has more of its bits allocated to the mantissa than the double-double
// has.
return std::numeric_limits<long double>::digits ==
2 * std::numeric_limits<double>::digits;
}
} // namespace numeric_internal
Y_ABSL_NAMESPACE_END
} // namespace y_absl
#endif // Y_ABSL_NUMERIC_INTERNAL_REPRESENTATION_H_
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