Compute a hash from the content of a stream and restore the position. - CSharp Security

CSharp examples for Security:Hash

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Description

Compute a hash from the content of a stream and restore the position.

Demo Code

// This file is subject to the terms and conditions defined in
using System.IO;/*ww  w  . j a va2 s.  co  m*/

public class Main{
        /// <summary>
        /// Compute a hash from the content of a stream and restore the position.
        /// </summary>
        /// <remarks>
        /// Modified FNV Hash in C#
        /// http://stackoverflow.com/a/468084
        /// </remarks>
        public static int ComputeHash(Stream stream)
        {
            System.Diagnostics.Debug.Assert(stream.CanSeek);

            unchecked
            {
                const int p = 16777619;
                var hash = (int)2166136261;

                var prevPosition = stream.Position;
                stream.Position = 0;

                var data = new byte[1024];
                int length;
                while((length = stream.Read(data, 0, data.Length)) != 0)
                {
                    for (var i = 0; i < length; i++)
                        hash = (hash ^ data[i]) * p;
                }

                // Restore stream position.
                stream.Position = prevPosition;

                hash += hash << 13;
                hash ^= hash >> 7;
                hash += hash << 3;
                hash ^= hash >> 17;
                hash += hash << 5;
                return hash;
            }
        }
        /// <summary>
        /// Compute a hash from a byte array.
        /// </summary>
        /// <remarks>
        /// Modified FNV Hash in C#
        /// http://stackoverflow.com/a/468084
        /// </remarks>
        public static int ComputeHash(params byte[] data)
        {
            unchecked
            {
                const int p = 16777619;
                var hash = (int)2166136261;

                for (var i = 0; i < data.Length; i++)
                    hash = (hash ^ data[i]) * p;

                hash += hash << 13;
                hash ^= hash >> 7;
                hash += hash << 3;
                hash ^= hash >> 17;
                hash += hash << 5;
                return hash;
            }
        }
}

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