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Diffstat (limited to 'csharp/src/Google.Protobuf/Collections/ProtobufEqualityComparers.cs')
| -rw-r--r-- | csharp/src/Google.Protobuf/Collections/ProtobufEqualityComparers.cs | 130 |
1 files changed, 130 insertions, 0 deletions
diff --git a/csharp/src/Google.Protobuf/Collections/ProtobufEqualityComparers.cs b/csharp/src/Google.Protobuf/Collections/ProtobufEqualityComparers.cs new file mode 100644 index 00000000..13ef60fc --- /dev/null +++ b/csharp/src/Google.Protobuf/Collections/ProtobufEqualityComparers.cs @@ -0,0 +1,130 @@ +#region Copyright notice and license +// Protocol Buffers - Google's data interchange format +// Copyright 2017 Google Inc. All rights reserved. +// https://developers.google.com/protocol-buffers/ +// +// Redistribution and use in source and binary forms, with or without +// modification, are permitted provided that the following conditions are +// met: +// +// * Redistributions of source code must retain the above copyright +// notice, this list of conditions and the following disclaimer. +// * Redistributions in binary form must reproduce the above +// copyright notice, this list of conditions and the following disclaimer +// in the documentation and/or other materials provided with the +// distribution. +// * Neither the name of Google Inc. nor the names of its +// contributors may be used to endorse or promote products derived from +// this software without specific prior written permission. +// +// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +#endregion + +using System; +using System.Collections.Generic; + +namespace Google.Protobuf.Collections +{ + /// <summary> + /// Provides a central place to implement equality comparisons, primarily for bitwise float/double equality. + /// </summary> + public static class ProtobufEqualityComparers + { + /// <summary> + /// Returns an equality comparer for <typeparamref name="T"/> suitable for Protobuf equality comparisons. + /// This is usually just the default equality comparer for the type, but floating point numbers are compared + /// bitwise. + /// </summary> + /// <typeparam name="T">The type of equality comparer to return.</typeparam> + /// <returns>The equality comparer.</returns> + public static EqualityComparer<T> GetEqualityComparer<T>() + { + return typeof(T) == typeof(double) ? (EqualityComparer<T>) (object) BitwiseDoubleEqualityComparer + : typeof(T) == typeof(float) ? (EqualityComparer<T>) (object) BitwiseSingleEqualityComparer + : typeof(T) == typeof(double?) ? (EqualityComparer<T>) (object) BitwiseNullableDoubleEqualityComparer + : typeof(T) == typeof(float?) ? (EqualityComparer<T>) (object) BitwiseNullableSingleEqualityComparer + : EqualityComparer<T>.Default; + } + + /// <summary> + /// Returns an equality comparer suitable for comparing 64-bit floating point values, by bitwise comparison. + /// (NaN values are considered equal, but only when they have the same representation.) + /// </summary> + public static EqualityComparer<double> BitwiseDoubleEqualityComparer { get; } = new BitwiseDoubleEqualityComparerImpl(); + + /// <summary> + /// Returns an equality comparer suitable for comparing 32-bit floating point values, by bitwise comparison. + /// (NaN values are considered equal, but only when they have the same representation.) + /// </summary> + public static EqualityComparer<float> BitwiseSingleEqualityComparer { get; } = new BitwiseSingleEqualityComparerImpl(); + + /// <summary> + /// Returns an equality comparer suitable for comparing nullable 64-bit floating point values, by bitwise comparison. + /// (NaN values are considered equal, but only when they have the same representation.) + /// </summary> + public static EqualityComparer<double?> BitwiseNullableDoubleEqualityComparer { get; } = new BitwiseNullableDoubleEqualityComparerImpl(); + + /// <summary> + /// Returns an equality comparer suitable for comparing nullable 32-bit floating point values, by bitwise comparison. + /// (NaN values are considered equal, but only when they have the same representation.) + /// </summary> + public static EqualityComparer<float?> BitwiseNullableSingleEqualityComparer { get; } = new BitwiseNullableSingleEqualityComparerImpl(); + + private class BitwiseDoubleEqualityComparerImpl : EqualityComparer<double> + { + public override bool Equals(double x, double y) => + BitConverter.DoubleToInt64Bits(x) == BitConverter.DoubleToInt64Bits(y); + + public override int GetHashCode(double obj) => + BitConverter.DoubleToInt64Bits(obj).GetHashCode(); + } + + private class BitwiseSingleEqualityComparerImpl : EqualityComparer<float> + { + // Just promote values to double and use BitConverter.DoubleToInt64Bits, + // as there's no BitConverter.SingleToInt32Bits, unfortunately. + + public override bool Equals(float x, float y) => + BitConverter.DoubleToInt64Bits(x) == BitConverter.DoubleToInt64Bits(y); + + public override int GetHashCode(float obj) => + BitConverter.DoubleToInt64Bits(obj).GetHashCode(); + } + + private class BitwiseNullableDoubleEqualityComparerImpl : EqualityComparer<double?> + { + public override bool Equals(double? x, double? y) => + x == null && y == null ? true + : x == null || y == null ? false + : BitwiseDoubleEqualityComparer.Equals(x.Value, y.Value); + + // The hash code for null is just a constant which is at least *unlikely* to be used + // elsewhere. (Compared with 0, say.) + public override int GetHashCode(double? obj) => + obj == null ? 293864 : BitwiseDoubleEqualityComparer.GetHashCode(obj.Value); + } + + private class BitwiseNullableSingleEqualityComparerImpl : EqualityComparer<float?> + { + public override bool Equals(float? x, float? y) => + x == null && y == null ? true + : x == null || y == null ? false + : BitwiseSingleEqualityComparer.Equals(x.Value, y.Value); + + // The hash code for null is just a constant which is at least *unlikely* to be used + // elsewhere. (Compared with 0, say.) + public override int GetHashCode(float? obj) => + obj == null ? 293864 : BitwiseSingleEqualityComparer.GetHashCode(obj.Value); + } + } +} |