// 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_