HashCodeCombiner - Useful for GetHashCode implementations!

HashCodeCombiner.cs

// Copied from http://aspnetwebstack.codeplex.com/SourceControl/latest#src/Common/HashCodeCombiner.cs
// Licensed under the Apache 2 License Terms as defined in http://aspnetwebstack.codeplex.com/SourceControl/latest#License.txt
// The only change made is to move the class to the System namespace to make it easily available in any project this file is included in.

// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

using System.Collections;

namespace System
{
    internal class HashCodeCombiner
    {
        private long _combinedHash64 = 0x1505L;

        public int CombinedHash
        {
            get { return _combinedHash64.GetHashCode(); }
        }

        public HashCodeCombiner Add(IEnumerable e)
        {
            if (e == null)
            {
                Add(0);
            }
            else
            {
                int count = 0;
                foreach (object o in e)
                {
                    Add(o);
                    count++;
                }
                Add(count);
            }
            return this;
        }

        public HashCodeCombiner Add(int i)
        {
            _combinedHash64 = ((_combinedHash64 << 5) + _combinedHash64) ^ i;
            return this;
        }

        public HashCodeCombiner Add(object o)
        {
            int hashCode = (o != null) ? o.GetHashCode() : 0;
            Add(hashCode);
            return this;
        }

        public static HashCodeCombiner Start()
        {
            return new HashCodeCombiner();
        }
    }
}