// 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 System.IO;
namespace SharpCompress.Compressors.Deflate
{
/// <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>
internal class CRC32
{
private const int BUFFER_SIZE = 8192;
private static readonly UInt32[] crc32Table;
private UInt32 runningCrc32Result = 0xFFFFFFFF;
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;
}
}
}
/// <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; private set; }
/// <summary>
/// Indicates the current CRC for all blocks slurped in.
/// </summary>
public Int32 Crc32Result => 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 UInt32 GetCrc32(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 UInt32 GetCrc32AndCopy(Stream input, Stream output)
{
if (input == null)
{
throw new ZlibException("The input stream must not be null.");
}
unchecked
{
//UInt32 crc32Result;
//crc32Result = 0xFFFFFFFF;
var 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 ~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.
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)
{
var even = new uint[32]; // even-power-of-two zeros operator
var odd = new uint[32]; // odd-power-of-two zeros operator
if (length == 0)
{
return;
}
uint crc1 = ~runningCrc32Result;
var 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);
var 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;
}
// private member vars
}
}