好几种CRC的编码方法
using System;
namespace Communication.IO.Tools
{
/// <summary>
/// Tool to calculate and add CRC codes to a string
///
/// ***************************************************************************
/// Copyright (c) 2003 Thoraxcentrum, Erasmus MC, The Netherlands.
///
/// Written by Marcel de Wijs with help from a lot of others,
/// especially Stefan Nelwan
///
/// This code is for free. I ported it from several different sources to C#.
///
/// For comments:
/// ***************************************************************************
/// </summary>
public class CRCTool
{
// 'order' [1..32] is the CRC polynom order, counted without the leading '1' bit
// 'polynom' is the CRC polynom without leading '1' bit
// 'direct' [0,1] specifies the kind of algorithm: 1=direct, no augmented zero bits
// 'crcinit' is the initial CRC value belonging to that algorithm
// 'crcxor' is the final XOR value
// 'refin' [0,1] specifies if a data byte is reflected before processing (UART) or not
// 'refout' [0,1] specifies if the CRC will be reflected before XOR
// Data character string
// For CRC-CCITT : order = 16, direct=1, poly=0x1021, CRCinit = 0xFFFF, crcxor=0; refin =0, refout=0
// For CRC16: order = 16, direct=1, poly=0x8005, CRCinit = 0x0, crcxor=0x0; refin =1, refout=1
// For CRC32: order = 32, direct=1, poly=0x4c11db7, CRCinit = 0xFFFFFFFF, crcxor=0xFFFFFFFF; refin =1, refout=1
// Default : CRC-CCITT
private int order = 16;
private ulong polynom = 0x1021;
private int direct = 1;
private ulong crcinit = 0xFFFF;
private ulong crcxor = 0x0;
private int refin = 0;
private int refout = 0;
private ulong crcmask;
private ulong crchighbit;
private ulong crcinit_direct;
private ulong crcinit_nondirect;
private ulong [] crctab = new ulong[256];
// Enumeration used in the init function to specify which CRC algorithm to use
public enum CRCCode{CRC_CCITT, CRC16, CRC32};
public CRCTool()
{
//
// TODO: Add constructor logic here
//
}
public void Init(CRCCode CodingType)
{
switch( CodingType )
{
case CRCCode.CRC_CCITT:
order = 16; direct=1; polynom=0x1021; crcinit = 0xFFFF; crcxor=0; refin =0; refout=0;
break;
case CRCCode.CRC16:
order = 16; direct=1; polynom=0x8005; crcinit = 0x0; crcxor=0x0; refin =1; refout=1;
break;
case CRCCode.CRC32:
order = 32; direct=1; polynom=0x4c11db7; crcinit = 0xFFFFFFFF; crcxor=0xFFFFFFFF; refin =1; refout=1;
break;
}
// Initialize all variables for seeding and builing based upon the given coding type
// at first, compute constant bit masks for whole CRC and CRC high bit
crcmask = ((((ulong)1<(order-1))-1)<1)|1;
crchighbit = (ulong)1<(order-1);
// generate lookup table
generate_crc_table();
ulong bit, crc;
int i;
if ( direct == 0 )
{
crcinit_nondirect = crcinit;
crc = crcinit;
for (i=0; i<order; i++)
{
bit = crc & crchighbit;
crc<= 1;
if ( bit != 0 )
{
crc^= polynom;
}
}
crc&= crcmask;
crcinit_direct = crc;
}
else
{
crcinit_direct = crcinit;
crc = crcinit;
for (i=0; i<order; i++)
{
bit = crc & 1;
if (bit != 0)
{
crc^= polynom;
}
crc >= 1;
if (bit != 0)
{
crc|= crchighbit;
}
}
crcinit_nondirect = crc;
}
}
/// <summary>
/// 4 ways to calculate the crc checksum. If you have to do a lot of encoding
/// you should use the table functions. Since they use precalculated values, which
/// saves some calculating.
/// </summary>.
public ulong crctablefast (byte[] p)
{
// fast lookup table algorithm without augmented zero bytes, e.g. used in pkzip.
// only usable with polynom orders of 8, 16, 24 or 32.
ulong crc = crcinit_direct;
if ( refin != 0 )
{
crc = reflect(crc, order);
}
if ( refin == 0 )
{
for ( int i = 0; i < p.Length; i++ )
{
crc = (crc < 8) ^ crctab[ ((crc > (order-8)) & 0xff) ^ p[i]];
}
}
else
{
for ( int i = 0; i < p.Length; i++ )
{
crc = (crc > 8) ^ crctab[ (crc & 0xff) ^ p[i]];
}
}
if ( (refout^refin) != 0 )
{
crc = reflect(crc, order);
}
crc^= crcxor;
crc&= crcmask;
return(crc);
}
public ulong crctable (byte[] p)
{
// normal lookup table algorithm with augmented zero bytes.
// only usable with polynom orders of 8, 16, 24 or 32.
ulong crc = crcinit_nondirect;
if ( refin != 0 )
{
crc = reflect(crc, order);
}
if ( refin == 0 )
{
for ( int i = 0; i < p.Length; i++ )
{
crc = ((crc < 8) | p[i]) ^ crctab[ (crc > (order-8)) & 0xff ];
}
}
else
{
for ( int i = 0; i < p.Length; i++ )
{
crc = (ulong)(( (int)(crc > 8) | (p[i] < (order-8))) ^ (int)crctab[ crc & 0xff ]);
}
}
if ( refin == 0 )
{
for ( int i = 0; i < order/8; i++ )
{
crc = (crc < 8) ^ crctab[ (crc > (order-8)) & 0xff];
}
}
else
{
for ( int i = 0; i < order/8; i++ )
{
crc = (crc > 8) ^ crctab[crc & 0xff];
}
}
if ( (refout^refin) != 0 )
{
crc = reflect(crc, order);
}
crc^= crcxor;
crc&= crcmask;
return(crc);
}
public ulong crcbitbybit(byte[] p)
{
// bit by bit algorithm with augmented zero bytes.
// does not use lookup table, suited for polynom orders between 1...32.
int i;
ulong j, c, bit;
ulong crc = crcinit_nondirect;
for (i=0; i<p.Length; i++)
{
c = (ulong)p[i];
if ( refin != 0 )
{
c = reflect(c, 8);
}
for (j=0x80; j != 0; j>=1)
{
bit = crc & crchighbit;
crc<= 1;
if ( (c & j) != 0)
{
crc|= 1;
}
if ( bit != 0 )
{
crc^= polynom;
}
}
}
for ( i=0; (int)i < order; i++)
{
bit = crc & crchighbit;
crc<= 1;
if ( bit != 0 ) crc^= polynom;
}
if ( refout != 0 )
{
crc=reflect(crc, order);
}
crc^= crcxor;
crc&= crcmask;
return(crc);
}
public ulong crcbitbybitfast(byte[] p)
{
// fast bit by bit algorithm without augmented zero bytes.
// does not use lookup table, suited for polynom orders between 1...32.
int i;
ulong j, c, bit;
ulong crc = crcinit_direct;
for (i = 0; i < p.Length; i++)
{
c = (ulong)p[i];
if ( refin != 0)
{
c = reflect(c, 8);
}
for ( j = 0x80; j > 0; j >= 1 )
{
bit = crc & crchighbit;
crc <= 1;
if ( (c & j) > 0 ) bit^= crchighbit;
if ( bit > 0 ) crc^= polynom;
}
}
if ( refout > 0)
{
crc=reflect( crc, order );
}
crc^= crcxor;
crc&= crcmask;
return(crc);
}
/// <summary>
/// CalcCRCITT is an algorithm found on the web for calculating the CRCITT checksum
/// It is included to demonstrate that although it looks different it is the same
/// routine as the crcbitbybit* functions. But it is optimized and preconfigured for CRCITT.
/// </summary>
public ushort CalcCRCITT(byte[] p)
{
uint uiCRCITTSum = 0xFFFF;
uint uiByteValue;
for (int iBufferIndex = 0; iBufferIndex < p.Length; iBufferIndex++)
{
uiByteValue = ( (uint) p[iBufferIndex] < 8);
for ( int iBitIndex = 0; iBitIndex < 8; iBitIndex++ )
{
if ( ( (uiCRCITTSum^uiByteValue) & 0x8000) != 0 )
{
uiCRCITTSum = (uiCRCITTSum <1 ) ^ 0x1021;
}
else
{
uiCRCITTSum <= 1;
}
uiByteValue <=1;
}
}
return (ushort)uiCRCITTSum;
}
#region subroutines
private ulong reflect (ulong crc, int bitnum)
{
// reflects the lower 'bitnum' bits of 'crc'
ulong i, j=1, crcout = 0;
for ( i = (ulong)1 <(bitnum-1); i != 0; i>=1)
{
if ( ( crc & i ) != 0 )
{
crcout |= j;
}
j<= 1;
}
return (crcout);
}
private void generate_crc_table()
{
// make CRC lookup table used by table algorithms
int i, j;
ulong bit, crc;
for (i=0; i<256; i++)
{
crc=(ulong)i;
if (refin != 0) // 'refin' [0,1] specifies if a data byte is reflected before processing (UART) or not
{
crc=reflect(crc, 8);
}
crc<= order-8;
for (j=0; j<8; j++)
{
bit = crc & crchighbit;
crc<= 1;
if ( bit !=0 ) crc^= polynom;
}
if (refin != 0)
{
crc = reflect(crc, order);
}
crc&= crcmask;
crctab[i]= crc;
}
}
#endregion
}
}