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