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//---------------------------------------------------------------------
// <copyright file="ByValueEqualityComparer.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//
// @owner Microsoft
// @backupOwner Microsoft
//---------------------------------------------------------------------
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Diagnostics;
using System.Linq;
namespace System.Data.Common.Utils
{
/// <summary>
/// An implementation of IEqualityComparer<object> that compares byte[] instances by value, and
/// delegates all other equality comparisons to a specified IEqualityComparer. In the default case,
/// this provides by-value comparison for instances of the CLR equivalents of all EDM primitive types.
/// </summary>
internal sealed class ByValueEqualityComparer : IEqualityComparer<object>
{
/// <summary>
/// Provides by-value comparison for instances of the CLR equivalents of all EDM primitive types.
/// </summary>
internal static readonly ByValueEqualityComparer Default = new ByValueEqualityComparer();
private ByValueEqualityComparer()
{
}
public new bool Equals(object x, object y)
{
if (object.Equals(x, y))
{
return true;
}
// If x and y are both non-null byte arrays, then perform a by-value comparison
// based on length and element values, otherwise defer to the default comparison.
//
byte[] xBytes = x as byte[];
byte[] yBytes = y as byte[];
if (xBytes != null && yBytes != null)
{
return CompareBinaryValues(xBytes, yBytes);
}
return false;
}
public int GetHashCode(object obj)
{
if (obj != null)
{
byte[] bytes = obj as byte[];
if (bytes != null)
{
return ComputeBinaryHashCode(bytes);
}
}
else
{
return 0;
}
return obj.GetHashCode();
}
internal static int ComputeBinaryHashCode(byte[] bytes)
{
Debug.Assert(bytes != null, "Byte array cannot be null");
int hashCode = 0;
for (int i = 0, n = Math.Min(bytes.Length, 7); i < n; i++)
{
hashCode = ((hashCode << 5) ^ bytes[i]);
}
return hashCode;
}
internal static bool CompareBinaryValues(byte[] first, byte[] second)
{
Debug.Assert(first != null && second != null, "Arguments cannot be null");
if (first.Length != second.Length)
{
return false;
}
for (int i = 0; i < first.Length; i++)
{
if (first[i] != second[i])
{
return false;
}
}
return true;
}
}
/// <summary>
/// Extends IComparer support to the (non-IComparable) byte[] type, based on by-value comparison.
/// </summary>
internal class ByValueComparer : IComparer
{
internal static readonly IComparer Default = new ByValueComparer(Comparer<object>.Default);
private readonly IComparer nonByValueComparer;
private ByValueComparer(IComparer comparer)
{
Debug.Assert(comparer != null, "Non-ByValue comparer cannot be null");
this.nonByValueComparer = comparer;
}
int IComparer.Compare(object x, object y)
{
if (object.ReferenceEquals(x, y))
{
return 0;
}
//We can convert DBNulls to nulls for the purposes of comparison.
Debug.Assert(!((object.ReferenceEquals(x, DBNull.Value)) && (object.ReferenceEquals(y,DBNull.Value))), "object.ReferenceEquals should catch the case when both values are dbnull");
if (object.ReferenceEquals(x, DBNull.Value))
{
x = null;
}
if (object.ReferenceEquals(y, DBNull.Value))
{
y = null;
}
if (x != null && y != null)
{
byte[] xAsBytes = x as byte[];
byte[] yAsBytes = y as byte[];
if (xAsBytes != null && yAsBytes != null)
{
int result = xAsBytes.Length - yAsBytes.Length;
if (result == 0)
{
int idx = 0;
while (result == 0 && idx < xAsBytes.Length)
{
byte xVal = xAsBytes[idx];
byte yVal = yAsBytes[idx];
if (xVal != yVal)
{
result = xVal - yVal;
}
idx++;
}
}
return result;
}
}
return this.nonByValueComparer.Compare(x, y);
}
}
}
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