// 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 ABSL_NUMERIC_INTERNAL_REPRESENTATION_H_

#define ABSL_NUMERIC_INTERNAL_REPRESENTATION_H_

#include <limits>

#include "absl/base/config.h"

namespace absl {

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

ABSL_NAMESPACE_END

}  // namespace absl

#endif  // ABSL_NUMERIC_INTERNAL_REPRESENTATION_H_