context: //
  // System.Security.Cryptography.HashAlgorithm.cs
  //
  // Authors:
  //	Matthew S. Ford (Matthew.S.Ford@Rose-Hulman.Edu)
  //	Sebastien Pouliot (sebastien@ximian.com)
  //
  // Copyright 2001 by Matthew S. Ford.
  // Portions (C) 2002 Motus Technologies Inc. (http://www.motus.com)
  // Copyright (C) 2004-2006 Novell, Inc (http://www.novell.com)
  //
  // Permission is hereby granted, free of charge, to any person obtaining
  // a copy of this software and associated documentation files (the
  // "Software"), to deal in the Software without restriction, including
  // without limitation the rights to use, copy, modify, merge, publish,
  // distribute, sublicense, and/or sell copies of the Software, and to
  // permit persons to whom the Software is furnished to do so, subject to
  // the following conditions:
  // 
  // The above copyright notice and this permission notice shall be
  // included in all copies or substantial portions of the Software.
  // 
  // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  // EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  // NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
  // LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
  // OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
  // WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  //
  
  using System.Globalization;
  using System.IO;
  using System.Runtime.InteropServices;
  
  namespace System.Security.Cryptography {
  
  	[ComVisible (true)]
  	public abstract class HashAlgorithm : ICryptoTransform {
  
  		protected internal byte[] HashValue;
  		protected int HashSizeValue;
  		protected int State;
  		private bool disposed;
  
  		protected HashAlgorithm () 
  		{
  			disposed = false;
  		}
  
  		public virtual bool CanTransformMultipleBlocks {
  			get { return true; }
  		}
  
  		public virtual bool CanReuseTransform {
  			get { return true; }
  		}
  
  		public void Clear () 
  		{
  			// same as System.IDisposable.Dispose() which is documented
  			Dispose (true);
  		}
  
  		public byte[] ComputeHash (byte[] buffer) 
  		{
  			if (buffer == null)
  				throw new ArgumentNullException ("buffer");
  
  			return ComputeHash (buffer, 0, buffer.Length);
  		}
  
  		public byte[] ComputeHash (byte[] buffer, int offset, int count) 
  		{
  			if (disposed)
  				throw new ObjectDisposedException ("HashAlgorithm");
  			if (buffer == null)
  				throw new ArgumentNullException ("buffer");
  			if (offset < 0)
  				throw new ArgumentOutOfRangeException ("offset", "< 0");
  			if (count < 0)
  				throw new ArgumentException ("count", "< 0");
  			// ordered to avoid possible integer overflow
  			if (offset > buffer.Length - count) {
  				throw new ArgumentException ("offset + count", 
  					Locale.GetText ("Overflow"));
  			}
  
  			HashCore (buffer, offset, count);
  			HashValue = HashFinal ();
  			Initialize ();
  			
  			return HashValue;
  		}
  
  		public byte[] ComputeHash (Stream inputStream) 
  		{
  			// don't read stream unless object is ready to use
  			if (disposed)
  				throw new ObjectDisposedException ("HashAlgorithm");
  
  			byte[] buffer = new byte [4096];
  			int len = inputStream.Read (buffer, 0, 4096);
  			while (len > 0) {
  				HashCore (buffer, 0, len);
  				len = inputStream.Read (buffer, 0, 4096);
  			}
  			HashValue = HashFinal ();
  			Initialize ();
  			return HashValue;
  		}
  	
  		public static HashAlgorithm Create () 
  		{
  #if FULL_AOT_RUNTIME
  			return new System.Security.Cryptography.SHA1CryptoServiceProvider ();
  #else
  			return Create ("System.Security.Cryptography.HashAlgorithm");
  #endif
  		}
  	
  		public static HashAlgorithm Create (string hashName)
  		{
  			return (HashAlgorithm) CryptoConfig.CreateFromName (hashName);
  		}
  	
  		public virtual byte[] Hash {
  			get { 
  				if (HashValue == null) {
  					throw new CryptographicUnexpectedOperationException (
  						Locale.GetText ("No hash value computed."));
  				}
  				return HashValue; 
  			}
  		}
  	
  		protected abstract void HashCore (byte[] array, int ibStart, int cbSize);
  
  		protected abstract byte[] HashFinal ();
  
  		public virtual int HashSize {
  			get { return HashSizeValue; }
  		}
  	
  		public abstract void Initialize ();
  
  		protected virtual void Dispose (bool disposing)
  		{
  			disposed = true;
  		}
  	
  		public virtual int InputBlockSize {
  			get { return 1; }
  		}
  	
  		public virtual int OutputBlockSize {
  			get { return 1; }
  		}
  
  #if NET_4_0
  		public void Dispose ()
  #else
  		void IDisposable.Dispose () 
  #endif
  		{
  			Dispose (true);
  			GC.SuppressFinalize (this);  // Finalization is now unnecessary
  		}
  
  		// LAMESPEC: outputBuffer is optional in 2.0 (i.e. can be null).
  		// However a null outputBuffer would throw a ExecutionEngineException under 1.x
  		public int TransformBlock (byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset) 
  		{
  			if (inputBuffer == null)
  				throw new ArgumentNullException ("inputBuffer");
  
  			if (inputOffset < 0)
  				throw new ArgumentOutOfRangeException ("inputOffset", "< 0");
  			if (inputCount < 0)
  				throw new ArgumentException ("inputCount");
  
  			// ordered to avoid possible integer overflow
  			if ((inputOffset < 0) || (inputOffset > inputBuffer.Length - inputCount))
  				throw new ArgumentException ("inputBuffer");
  
  			if (outputBuffer != null) {
  				if (outputOffset < 0) {
  					throw new ArgumentOutOfRangeException ("outputOffset", "< 0");
  				}
  				// ordered to avoid possible integer overflow
  				if (outputOffset > outputBuffer.Length - inputCount) {
  					throw new ArgumentException ("outputOffset + inputCount", 
  						Locale.GetText ("Overflow"));
  				}
  			}
  
  			HashCore (inputBuffer, inputOffset, inputCount);
  
  			if (outputBuffer != null)
  				Buffer.BlockCopy (inputBuffer, inputOffset, outputBuffer, outputOffset, inputCount);
  
  			return inputCount;
  		}
  	
  		public byte[] TransformFinalBlock (byte[] inputBuffer, int inputOffset, int inputCount) 
  		{
  			if (inputBuffer == null)
  				throw new ArgumentNullException ("inputBuffer");
  			if (inputCount < 0)
  
gt: 				throw new ArgumentException ("inputCount");