// Crc32.cs
// ------------------------------------------------------------------
//
// Copyright (c) 2006-2009 Dino Chiesa and Microsoft Corporation.
// All rights reserved.
//
// This code module is part of DotNetZip, a zipfile class library.
//
// ------------------------------------------------------------------
//
// This code is licensed under the Microsoft Public License.
// See the file License.txt for the license details.
// More info on: http://dotnetzip.codeplex.com
//
// ------------------------------------------------------------------
//
// last saved (in emacs):
// Time-stamp: <2010-January-16 13:16:27>
//
// ------------------------------------------------------------------
//
// Implements the CRC algorithm, which is used in zip files. The zip format calls for
// the zipfile to contain a CRC for the unencrypted byte stream of each file.
//
// It is based on example source code published at
// http://www.vbaccelerator.com/home/net/code/libraries/CRC32/Crc32_zip_CRC32_CRC32_cs.asp
//
// This implementation adds a tweak of that code for use within zip creation. While
// computing the CRC we also compress the byte stream, in the same read loop. This
// avoids the need to read through the uncompressed stream twice - once to compute CRC
// and another time to compress.
//
// ------------------------------------------------------------------
using System;
using Interop=System.Runtime.InteropServices;
namespace Ionic.Zlib
{
/// <summary>
/// Calculates a 32bit Cyclic Redundancy Checksum (CRC) using the same polynomial
/// used by Zip. This type is used internally by DotNetZip; it is generally not used
/// directly by applications wishing to create, read, or manipulate zip archive
/// files.
/// </summary>
[Interop.GuidAttribute("ebc25cf6-9120-4283-b972-0e5520d0000C")]
[Interop.ComVisible(true)]
#if !NETCF
[Interop.ClassInterface(Interop.ClassInterfaceType.AutoDispatch)]
#endif
public class CRC32
{
/// <summary>
/// indicates the total number of bytes read on the CRC stream.
/// This is used when writing the ZipDirEntry when compressing files.
/// </summary>
public Int64 TotalBytesRead
{
get
{
return _TotalBytesRead;
}
}
/// <summary>
/// Indicates the current CRC for all blocks slurped in.
/// </summary>
public Int32 Crc32Result
{
get
{
// return one's complement of the running result
return unchecked((Int32)(~_RunningCrc32Result));
}
}
/// <summary>
/// Returns the CRC32 for the specified stream.
/// </summary>
/// <param name="input">The stream over which to calculate the CRC32</param>
/// <returns>the CRC32 calculation</returns>
public Int32 GetCrc32(System.IO.Stream input)
{
return GetCrc32AndCopy(input, null);
}
/// <summary>
/// Returns the CRC32 for the specified stream, and writes the input into the
/// output stream.
/// </summary>
/// <param name="input">The stream over which to calculate the CRC32</param>
/// <param name="output">The stream into which to deflate the input</param>
/// <returns>the CRC32 calculation</returns>
public Int32 GetCrc32AndCopy(System.IO.Stream input, System.IO.Stream output)
{
if (input == null)
throw new ZlibException("The input stream must not be null.");
unchecked
{
//UInt32 crc32Result;
//crc32Result = 0xFFFFFFFF;
byte[] buffer = new byte[BUFFER_SIZE];
int readSize = BUFFER_SIZE;
_TotalBytesRead = 0;
int count = input.Read(buffer, 0, readSize);
if (output != null) output.Write(buffer, 0, count);
_TotalBytesRead += count;
while (count > 0)
{
SlurpBlock(buffer, 0, count);
count = input.Read(buffer, 0, readSize);
if (output != null) output.Write(buffer, 0, count);
_TotalBytesRead += count;
}
return (Int32)(~_RunningCrc32Result);
}
}
/// <summary>
/// Get the CRC32 for the given (word,byte) combo. This is a computation
/// defined by PKzip.
/// </summary>
/// <param name="W">The word to start with.</param>
/// <param name="B">The byte to combine it with.</param>
/// <returns>The CRC-ized result.</returns>
public Int32 ComputeCrc32(Int32 W, byte B)
{
return _InternalComputeCrc32((UInt32)W, B);
}
internal Int32 _InternalComputeCrc32(UInt32 W, byte B)
{
return (Int32)(crc32Table[(W ^ B) & 0xFF] ^ (W >> 8));
}
/// <summary>
/// Update the value for the running CRC32 using the given block of bytes.
/// This is useful when using the CRC32() class in a Stream.
/// </summary>
/// <param name="block">block of bytes to slurp</param>
/// <param name="offset">starting point in the block</param>
/// <param name="count">how many bytes within the block to slurp</param>
public void SlurpBlock(byte[] block, int offset, int count)
{
if (block == null)
throw new ZlibException("The data buffer must not be null.");
for (int i = 0; i < count; i++)
{
int x = offset + i;
_RunningCrc32Result = ((_RunningCrc32Result) >> 8) ^ crc32Table[(block[x]) ^ ((_RunningCrc32Result) & 0x000000FF)];
}
_TotalBytesRead += count;
}
// pre-initialize the crc table for speed of lookup.
static CRC32()
{
unchecked
{
// PKZip specifies CRC32 with a polynomial of 0xEDB88320;
// This is also the CRC-32 polynomial used bby Ethernet, FDDI,
// bzip2, gzip, and others.
// Often the polynomial is shown reversed as 0x04C11DB7.
// For more details, see http://en.wikipedia.org/wiki/Cyclic_redundancy_check
UInt32 dwPolynomial = 0xEDB88320;
UInt32 i, j;
crc32Table = new UInt32[256];
UInt32 dwCrc;
for (i = 0; i < 256; i++)
{
dwCrc = i;
for (j = 8; j > 0; j--)
{
if ((dwCrc & 1) == 1)
{
dwCrc = (dwCrc >> 1) ^ dwPolynomial;
}
else
{
dwCrc >>= 1;
}
}
crc32Table[i] = dwCrc;
}
}
}
private uint gf2_matrix_times(uint[] matrix, uint vec)
{
uint sum = 0;
int i=0;
while (vec != 0)
{
if ((vec & 0x01)== 0x01)
sum ^= matrix[i];
vec >>= 1;
i++;
}
return sum;
}
private void gf2_matrix_square(uint[] square, uint[] mat)
{
for (int i = 0; i < 32; i++)
square[i] = gf2_matrix_times(mat, mat[i]);
}
/// <summary>
/// Combines the given CRC32 value with the current running total.
/// </summary>
/// <remarks>
/// This is useful when using a divide-and-conquer approach to calculating a CRC.
/// Multiple threads can each calculate a CRC32 on a segment of the data, and then
/// combine the individual CRC32 values at the end.
/// </remarks>
/// <param name="crc">the crc value to be combined with this one</param>
/// <param name="length">the length of data the CRC value was calculated on</param>
public void Combine(int crc, int length)
{
uint[] even = new uint[32]; // even-power-of-two zeros operator
uint[] odd = new uint[32]; // odd-power-of-two zeros operator
if (length == 0)
return;
uint crc1= ~_RunningCrc32Result;
uint crc2= (uint) crc;
// put operator for one zero bit in odd
odd[0] = 0xEDB88320; // the CRC-32 polynomial
uint row = 1;
for (int i = 1; i < 32; i++)
{
odd[i] = row;
row <<= 1;
}
// put operator for two zero bits in even
gf2_matrix_square(even, odd);
// put operator for four zero bits in odd
gf2_matrix_square(odd, even);
uint len2 = (uint) length;
// apply len2 zeros to crc1 (first square will put the operator for one
// zero byte, eight zero bits, in even)
do {
// apply zeros operator for this bit of len2
gf2_matrix_square(even, odd);
if ((len2 & 1)== 1)
crc1 = gf2_matrix_times(even, crc1);
len2 >>= 1;
if (len2 == 0)
break;
// another iteration of the loop with odd and even swapped
gf2_matrix_square(odd, even);
if ((len2 & 1)==1)
crc1 = gf2_matrix_times(odd, crc1);
len2 >>= 1;
} while (len2 != 0);
crc1 ^= crc2;
_RunningCrc32Result= ~crc1;
//return (int) crc1;
return;
}
// private member vars
private Int64 _TotalBytesRead;
private static readonly UInt32[] crc32Table;
private const int BUFFER_SIZE = 8192;
private UInt32 _RunningCrc32Result = 0xFFFFFFFF;
}
/// <summary>
/// A Stream that calculates a CRC32 (a checksum) on all bytes read,
/// or on all bytes written.
/// </summary>
///
/// <remarks>
/// <para>
/// This class can be used to verify the CRC of a ZipEntry when
/// reading from a stream, or to calculate a CRC when writing to a
/// stream. The stream should be used to either read, or write, but
/// not both. If you intermix reads and writes, the results are not
/// defined.
/// </para>
///
/// <para>
/// This class is intended primarily for use internally by the
/// DotNetZip library.
/// </para>
/// </remarks>
public class CrcCalculatorStream : System.IO.Stream, System.IDisposable
{
private static readonly Int64 UnsetLengthLimit = -99;
internal System.IO.Stream _innerStream;
private CRC32 _Crc32;
private Int64 _lengthLimit = -99;
private bool _leaveOpen;
/// <summary>
/// Gets the total number of bytes run through the CRC32 calculator.
/// </summary>
///
/// <remarks>
/// This is either the total number of bytes read, or the total number of bytes
/// written, depending on the direction of this stream.
/// </remarks>
public Int64 TotalBytesSlurped
{
get { return _Crc32.TotalBytesRead; }
}
/// <summary>
/// The default constructor.
/// </summary>
/// <remarks>
/// Instances returned from this constructor will leave the underlying stream
/// open upon Close().
/// </remarks>
/// <param name="stream">The underlying stream</param>
public CrcCalculatorStream(System.IO.Stream stream)
: this(true, CrcCalculatorStream.UnsetLengthLimit, stream)
{
}
/// <summary>
/// The constructor allows the caller to specify how to handle the underlying
/// stream at close.
/// </summary>
/// <param name="stream">The underlying stream</param>
/// <param name="leaveOpen">true to leave the underlying stream
/// open upon close of the CrcCalculatorStream.; false otherwise.</param>
public CrcCalculatorStream(System.IO.Stream stream, bool leaveOpen)
: this(leaveOpen, CrcCalculatorStream.UnsetLengthLimit, stream)
{
}
/// <summary>
/// A constructor allowing the specification of the length of the stream to read.
/// </summary>
/// <remarks>
/// Instances returned from this constructor will leave the underlying stream open
/// upon Close().
/// </remarks>
/// <param name="stream">The underlying stream</param>
/// <param name="length">The length of the stream to slurp</param>
public CrcCalculatorStream(System.IO.Stream stream, Int64 length)
: this(true, length, stream)
{
if (length < 0)
throw new ArgumentException("length");
}
/// <summary>
/// A constructor allowing the specification of the length of the stream to
/// read, as well as whether to keep the underlying stream open upon Close().
/// </summary>
/// <param name="stream">The underlying stream</param>
/// <param name="length">The length of the stream to slurp</param>
/// <param name="leaveOpen">true to leave the underlying stream
/// open upon close of the CrcCalculatorStream.; false otherwise.</param>
public CrcCalculatorStream(System.IO.Stream stream, Int64 length, bool leaveOpen)
: this(leaveOpen, length, stream)
{
if (length < 0)
throw new ArgumentException("length");
}
// This ctor is private - no validation is done here. This is to allow the use
// of a (specific) negative value for the _lengthLimit, to indicate that there
// is no length set. So we validate the length limit in those ctors that use an
// explicit param, otherwise we don't validate, because it could be our special
// value.
private CrcCalculatorStream(bool leaveOpen, Int64 length, System.IO.Stream stream)
: base()
{
_innerStream = stream;
_Crc32 = new CRC32();
_lengthLimit = length;
_leaveOpen = leaveOpen;
}
/// <summary>
/// Provides the current CRC for all blocks slurped in.
/// </summary>
public Int32 Crc
{
get { return _Crc32.Crc32Result; }
}
/// <summary>
/// Indicates whether the underlying stream will be left open when the
/// CrcCalculatorStream is Closed.
/// </summary>
public bool LeaveOpen
{
get { return _leaveOpen; }
set { _leaveOpen = value; }
}
/// <summary>
/// Read from the stream
/// </summary>
/// <param name="buffer">the buffer to read</param>
/// <param name="offset">the offset at which to start</param>
/// <param name="count">the number of bytes to read</param>
/// <returns>the number of bytes actually read</returns>
public override int Read(byte[] buffer, int offset, int count)
{
int bytesToRead = count;
// Need to limit the # of bytes returned, if the stream is intended to have
// a definite length. This is especially useful when returning a stream for
// the uncompressed data directly to the application. The app won't
// necessarily read only the UncompressedSize number of bytes. For example
// wrapping the stream returned from OpenReader() into a StreadReader() and
// calling ReadToEnd() on it, We can "over-read" the zip data and get a
// corrupt string. The length limits that, prevents that problem.
if (_lengthLimit != CrcCalculatorStream.UnsetLengthLimit)
{
if (_Crc32.TotalBytesRead >= _lengthLimit) return 0; // EOF
Int64 bytesRemaining = _lengthLimit - _Crc32.TotalBytesRead;
if (bytesRemaining < count) bytesToRead = (int)bytesRemaining;
}
int n = _innerStream.Read(buffer, offset, bytesToRead);
if (n > 0) _Crc32.SlurpBlock(buffer, offset, n);
return n;
}
/// <summary>
/// Write to the stream.
/// </summary>
/// <param name="buffer">the buffer from which to write</param>
/// <param name="offset">the offset at which to start writing</param>
/// <param name="count">the number of bytes to write</param>
public override void Write(byte[] buffer, int offset, int count)
{
if (count > 0) _Crc32.SlurpBlock(buffer, offset, count);
_innerStream.Write(buffer, offset, count);
}
/// <summary>
/// Indicates whether the stream supports reading.
/// </summary>
public override bool CanRead
{
get { return _innerStream.CanRead; }
}
/// <summary>
/// Indicates whether the stream supports seeking.
/// </summary>
public override bool CanSeek
{
get { return _innerStream.CanSeek; }
}
/// <summary>
/// Indicates whether the stream supports writing.
/// </summary>
public override bool CanWrite
{
get { return _innerStream.CanWrite; }
}
/// <summary>
/// Flush the stream.
/// </summary>
public override void Flush()
{
_innerStream.Flush();
}
/// <summary>
/// Not implemented.
/// </summary>
public override long Length
{
get
{
if (_lengthLimit == CrcCalculatorStream.UnsetLengthLimit)
return _innerStream.Length;
else return _lengthLimit;
}
}
/// <summary>
/// Not implemented.
/// </summary>
public override long Position
{
get { return _Crc32.TotalBytesRead; }
set { throw new NotImplementedException(); }
}
/// <summary>
/// Not implemented.
/// </summary>
/// <param name="offset">N/A</param>
/// <param name="origin">N/A</param>
/// <returns>N/A</returns>
public override long Seek(long offset, System.IO.SeekOrigin origin)
{
throw new NotImplementedException();
}
/// <summary>
/// Not implemented.
/// </summary>
/// <param name="value">N/A</param>
public override void SetLength(long value)
{
throw new NotImplementedException();
}
void IDisposable.Dispose()
{
Close();
}
/// <summary>
/// Closes the stream.
/// </summary>
public override void Close()
{
base.Close();
if (!_leaveOpen)
_innerStream.Close();
}
}
}
Submit an article or tip