| // 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. | |
| 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 | |