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#region Copyright notice and license |
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// Protocol Buffers - Google's data interchange format |
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// Copyright 2017 Google Inc. All rights reserved. |
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// https://developers.google.com/protocol-buffers/ |
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// |
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// Redistribution and use in source and binary forms, with or without |
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// modification, are permitted provided that the following conditions are |
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// met: |
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// |
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// * Redistributions of source code must retain the above copyright |
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// notice, this list of conditions and the following disclaimer. |
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// * Redistributions in binary form must reproduce the above |
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// copyright notice, this list of conditions and the following disclaimer |
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// in the documentation and/or other materials provided with the |
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// distribution. |
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// * Neither the name of Google Inc. nor the names of its |
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// contributors may be used to endorse or promote products derived from |
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// this software without specific prior written permission. |
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// |
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS |
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT |
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR |
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT |
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, |
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT |
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, |
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY |
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT |
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE |
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. |
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#endregion |
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using System; |
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using System.Collections.Generic; |
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namespace Google.Protobuf.Collections |
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{ |
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/// <summary> |
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/// Provides a central place to implement equality comparisons, primarily for bitwise float/double equality. |
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/// </summary> |
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public static class ProtobufEqualityComparers |
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{ |
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/// <summary> |
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/// Returns an equality comparer for <typeparamref name="T"/> suitable for Protobuf equality comparisons. |
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/// This is usually just the default equality comparer for the type, but floating point numbers are compared |
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/// bitwise. |
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/// </summary> |
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/// <typeparam name="T">The type of equality comparer to return.</typeparam> |
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/// <returns>The equality comparer.</returns> |
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public static EqualityComparer<T> GetEqualityComparer<T>() |
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{ |
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return typeof(T) == typeof(double) ? (EqualityComparer<T>) (object) BitwiseDoubleEqualityComparer |
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: typeof(T) == typeof(float) ? (EqualityComparer<T>) (object) BitwiseSingleEqualityComparer |
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: typeof(T) == typeof(double?) ? (EqualityComparer<T>) (object) BitwiseNullableDoubleEqualityComparer |
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: typeof(T) == typeof(float?) ? (EqualityComparer<T>) (object) BitwiseNullableSingleEqualityComparer |
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: EqualityComparer<T>.Default; |
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} |
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/// <summary> |
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/// Returns an equality comparer suitable for comparing 64-bit floating point values, by bitwise comparison. |
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/// (NaN values are considered equal, but only when they have the same representation.) |
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/// </summary> |
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public static EqualityComparer<double> BitwiseDoubleEqualityComparer { get; } = new BitwiseDoubleEqualityComparerImpl(); |
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/// <summary> |
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/// Returns an equality comparer suitable for comparing 32-bit floating point values, by bitwise comparison. |
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/// (NaN values are considered equal, but only when they have the same representation.) |
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/// </summary> |
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public static EqualityComparer<float> BitwiseSingleEqualityComparer { get; } = new BitwiseSingleEqualityComparerImpl(); |
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/// <summary> |
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/// Returns an equality comparer suitable for comparing nullable 64-bit floating point values, by bitwise comparison. |
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/// (NaN values are considered equal, but only when they have the same representation.) |
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/// </summary> |
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public static EqualityComparer<double?> BitwiseNullableDoubleEqualityComparer { get; } = new BitwiseNullableDoubleEqualityComparerImpl(); |
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/// <summary> |
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/// Returns an equality comparer suitable for comparing nullable 32-bit floating point values, by bitwise comparison. |
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/// (NaN values are considered equal, but only when they have the same representation.) |
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/// </summary> |
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public static EqualityComparer<float?> BitwiseNullableSingleEqualityComparer { get; } = new BitwiseNullableSingleEqualityComparerImpl(); |
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private class BitwiseDoubleEqualityComparerImpl : EqualityComparer<double> |
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{ |
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public override bool Equals(double x, double y) => |
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BitConverter.DoubleToInt64Bits(x) == BitConverter.DoubleToInt64Bits(y); |
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public override int GetHashCode(double obj) => |
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BitConverter.DoubleToInt64Bits(obj).GetHashCode(); |
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} |
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private class BitwiseSingleEqualityComparerImpl : EqualityComparer<float> |
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{ |
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// Just promote values to double and use BitConverter.DoubleToInt64Bits, |
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// as there's no BitConverter.SingleToInt32Bits, unfortunately. |
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public override bool Equals(float x, float y) => |
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BitConverter.DoubleToInt64Bits(x) == BitConverter.DoubleToInt64Bits(y); |
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public override int GetHashCode(float obj) => |
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BitConverter.DoubleToInt64Bits(obj).GetHashCode(); |
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} |
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private class BitwiseNullableDoubleEqualityComparerImpl : EqualityComparer<double?> |
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{ |
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public override bool Equals(double? x, double? y) => |
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x == null && y == null ? true |
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: x == null || y == null ? false |
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: BitwiseDoubleEqualityComparer.Equals(x.Value, y.Value); |
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// The hash code for null is just a constant which is at least *unlikely* to be used |
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// elsewhere. (Compared with 0, say.) |
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public override int GetHashCode(double? obj) => |
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obj == null ? 293864 : BitwiseDoubleEqualityComparer.GetHashCode(obj.Value); |
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} |
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private class BitwiseNullableSingleEqualityComparerImpl : EqualityComparer<float?> |
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{ |
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public override bool Equals(float? x, float? y) => |
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x == null && y == null ? true |
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: x == null || y == null ? false |
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: BitwiseSingleEqualityComparer.Equals(x.Value, y.Value); |
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// The hash code for null is just a constant which is at least *unlikely* to be used |
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// elsewhere. (Compared with 0, say.) |
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public override int GetHashCode(float? obj) => |
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obj == null ? 293864 : BitwiseSingleEqualityComparer.GetHashCode(obj.Value); |
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} |
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} |
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} |
Jon Skeet
8 years ago
committed by
Jon Skeet