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#region Copyright notice and license
// Protocol Buffers - Google's data interchange format
// Copyright 2017 Google Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
#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);
}
}
}