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陈彬
2020-07-09 08:50:24 +08:00
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// CRC32.cs
// ------------------------------------------------------------------
//
// Copyright (c) 2011 Dino Chiesa.
// 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: <2011-August-02 18:25:54>
//
// ------------------------------------------------------------------
//
// This module defines the CRC32 class, which can do the CRC32 algorithm, using
// arbitrary starting polynomials, and bit reversal. The bit reversal is what
// distinguishes this CRC-32 used in BZip2 from the CRC-32 that is used in PKZIP
// files, or GZIP files. This class does both.
//
// ------------------------------------------------------------------
using System;
using Interop = System.Runtime.InteropServices;
namespace BestHTTP.Decompression.Crc
{
/// <summary>
/// Computes a CRC-32. The CRC-32 algorithm is parameterized - you
/// can set the polynomial and enable or disable bit
/// reversal. This can be used for GZIP, BZip2, or ZIP.
/// </summary>
/// <remarks>
/// This type is used internally by DotNetZip; it is generally not used
/// directly by applications wishing to create, read, or manipulate zip
/// archive files.
/// </remarks>
internal class CRC32
{
/// <summary>
/// Indicates the total number of bytes applied to the CRC.
/// </summary>
public Int64 TotalBytesRead
{
get
{
return _TotalBytesRead;
}
}
/// <summary>
/// Indicates the current CRC for all blocks slurped in.
/// </summary>
public Int32 Crc32Result
{
get
{
return unchecked((Int32)(~_register));
}
}
/// <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 Exception("The input stream must not be null.");
unchecked
{
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)(~_register);
}
}
/// <summary>
/// Get the CRC32 for the given (word,byte) combo. This is a
/// computation defined by PKzip for PKZIP 2.0 (weak) encryption.
/// </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 Exception("The data buffer must not be null.");
// bzip algorithm
for (int i = 0; i < count; i++)
{
int x = offset + i;
byte b = block[x];
if (this.reverseBits)
{
UInt32 temp = (_register >> 24) ^ b;
_register = (_register << 8) ^ crc32Table[temp];
}
else
{
UInt32 temp = (_register & 0x000000FF) ^ b;
_register = (_register >> 8) ^ crc32Table[temp];
}
}
_TotalBytesRead += count;
}
/// <summary>
/// Process one byte in the CRC.
/// </summary>
/// <param name = "b">the byte to include into the CRC . </param>
public void UpdateCRC(byte b)
{
if (this.reverseBits)
{
UInt32 temp = (_register >> 24) ^ b;
_register = (_register << 8) ^ crc32Table[temp];
}
else
{
UInt32 temp = (_register & 0x000000FF) ^ b;
_register = (_register >> 8) ^ crc32Table[temp];
}
}
/// <summary>
/// Process a run of N identical bytes into the CRC.
/// </summary>
/// <remarks>
/// <para>
/// This method serves as an optimization for updating the CRC when a
/// run of identical bytes is found. Rather than passing in a buffer of
/// length n, containing all identical bytes b, this method accepts the
/// byte value and the length of the (virtual) buffer - the length of
/// the run.
/// </para>
/// </remarks>
/// <param name = "b">the byte to include into the CRC. </param>
/// <param name = "n">the number of times that byte should be repeated. </param>
public void UpdateCRC(byte b, int n)
{
while (n-- > 0)
{
if (this.reverseBits)
{
uint temp = (_register >> 24) ^ b;
_register = (_register << 8) ^ crc32Table[(temp >= 0)
? temp
: (temp + 256)];
}
else
{
UInt32 temp = (_register & 0x000000FF) ^ b;
_register = (_register >> 8) ^ crc32Table[(temp >= 0)
? temp
: (temp + 256)];
}
}
}
private static uint ReverseBits(uint data)
{
unchecked
{
uint ret = data;
ret = (ret & 0x55555555) << 1 | (ret >> 1) & 0x55555555;
ret = (ret & 0x33333333) << 2 | (ret >> 2) & 0x33333333;
ret = (ret & 0x0F0F0F0F) << 4 | (ret >> 4) & 0x0F0F0F0F;
ret = (ret << 24) | ((ret & 0xFF00) << 8) | ((ret >> 8) & 0xFF00) | (ret >> 24);
return ret;
}
}
private static byte ReverseBits(byte data)
{
unchecked
{
uint u = (uint)data * 0x00020202;
uint m = 0x01044010;
uint s = u & m;
uint t = (u << 2) & (m << 1);
return (byte)((0x01001001 * (s + t)) >> 24);
}
}
private void GenerateLookupTable()
{
crc32Table = new UInt32[256];
unchecked
{
UInt32 dwCrc;
byte i = 0;
do
{
dwCrc = i;
for (byte j = 8; j > 0; j--)
{
if ((dwCrc & 1) == 1)
{
dwCrc = (dwCrc >> 1) ^ dwPolynomial;
}
else
{
dwCrc >>= 1;
}
}
if (reverseBits)
{
crc32Table[ReverseBits(i)] = ReverseBits(dwCrc);
}
else
{
crc32Table[i] = dwCrc;
}
i++;
} while (i!=0);
}
#if VERBOSE
Console.WriteLine();
Console.WriteLine("private static readonly UInt32[] crc32Table = {");
for (int i = 0; i < crc32Table.Length; i+=4)
{
Console.Write(" ");
for (int j=0; j < 4; j++)
{
Console.Write(" 0x{0:X8}U,", crc32Table[i+j]);
}
Console.WriteLine();
}
Console.WriteLine("};");
Console.WriteLine();
#endif
}
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= ~_register;
uint crc2= (uint) crc;
// put operator for one zero bit in odd
odd[0] = this.dwPolynomial; // 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;
_register= ~crc1;
//return (int) crc1;
return;
}
/// <summary>
/// Create an instance of the CRC32 class using the default settings: no
/// bit reversal, and a polynomial of 0xEDB88320.
/// </summary>
public CRC32() : this(false)
{
}
/// <summary>
/// Create an instance of the CRC32 class, specifying whether to reverse
/// data bits or not.
/// </summary>
/// <param name='reverseBits'>
/// specify true if the instance should reverse data bits.
/// </param>
/// <remarks>
/// <para>
/// In the CRC-32 used by BZip2, the bits are reversed. Therefore if you
/// want a CRC32 with compatibility with BZip2, you should pass true
/// here. In the CRC-32 used by GZIP and PKZIP, the bits are not
/// reversed; Therefore if you want a CRC32 with compatibility with
/// those, you should pass false.
/// </para>
/// </remarks>
public CRC32(bool reverseBits) :
this( unchecked((int)0xEDB88320), reverseBits)
{
}
/// <summary>
/// Create an instance of the CRC32 class, specifying the polynomial and
/// whether to reverse data bits or not.
/// </summary>
/// <param name='polynomial'>
/// The polynomial to use for the CRC, expressed in the reversed (LSB)
/// format: the highest ordered bit in the polynomial value is the
/// coefficient of the 0th power; the second-highest order bit is the
/// coefficient of the 1 power, and so on. Expressed this way, the
/// polynomial for the CRC-32C used in IEEE 802.3, is 0xEDB88320.
/// </param>
/// <param name='reverseBits'>
/// specify true if the instance should reverse data bits.
/// </param>
///
/// <remarks>
/// <para>
/// In the CRC-32 used by BZip2, the bits are reversed. Therefore if you
/// want a CRC32 with compatibility with BZip2, you should pass true
/// here for the <c>reverseBits</c> parameter. In the CRC-32 used by
/// GZIP and PKZIP, the bits are not reversed; Therefore if you want a
/// CRC32 with compatibility with those, you should pass false for the
/// <c>reverseBits</c> parameter.
/// </para>
/// </remarks>
public CRC32(int polynomial, bool reverseBits)
{
this.reverseBits = reverseBits;
this.dwPolynomial = (uint) polynomial;
this.GenerateLookupTable();
}
/// <summary>
/// Reset the CRC-32 class - clear the CRC "remainder register."
/// </summary>
/// <remarks>
/// <para>
/// Use this when employing a single instance of this class to compute
/// multiple, distinct CRCs on multiple, distinct data blocks.
/// </para>
/// </remarks>
public void Reset()
{
_register = 0xFFFFFFFFU;
}
// private member vars
private UInt32 dwPolynomial;
private Int64 _TotalBytesRead;
private bool reverseBits;
private UInt32[] crc32Table;
private const int BUFFER_SIZE = 8192;
private UInt32 _register = 0xFFFFFFFFU;
}
}