crc.c

CRC16 和 26位缩短码前向纠错计算

//###########################################################################
// FILE:	crc.c
// TITLE:	Calculation CRC value of Uart data stream,and do code fore correct.
//
// Description: CRC generation equation is g(x)=x^16+x^12+x^5+1
//
//              FEC generation equation is g(x)=x^10+x^8+x^7+x^5+x^4+x^3+1
//         
// History: Ver1.0,Octomber 7,2008,by Alex Zhang
//
//###########################################################################

#include "crc.h"

#define GCRC 0x11021
#define GCORRECT 0x5b9//101,1011,1001

unsigned int CrcTable[256];
unsigned int CorrectErfSample[26];
unsigned long CorrectTable[26];

void CrcInit(void)
{
  CreateCrcTable();
  CreateCorrectTable();
}

//Create CRC Table
void CreateCrcTable(void)
{
  unsigned int i,j;
  unsigned long t;
  for(i=0;i<256;i++){
    t = i<<8;
    for(j=0;j<8;j++){
      t <<= 1;
      if((t & (unsigned long)0x10000) != 0)
        t ^= (unsigned long)GCRC;
    }
    CrcTable[i] = t & (unsigned long)0x0000ffff;
  }
}

//Create FEC Corect table
void CreateCorrectTable(void)
{
  unsigned int i,j;
  unsigned long t;

  j = 0x80;
  for(i=0;i<8;i++){
    CorrectErfSample[i] = CorrectCreate(j,0);
    j >>= 1;
  }
  j = 0x80;
  for(i=0;i<8;i++){
    CorrectErfSample[i+8] = CorrectCreate(0,j);
    j >>= 1;
  }
  j = 0x200;
  for(i=0;i<10;i++){
    CorrectErfSample[i+16] = j;
    j >>= 1;
  }
  t = (unsigned long)1<<25;
  for(i=0;i<26;i++){
    CorrectTable[i] = t;
    t >>= 1;
  }
}

//Create Crc Code
unsigned int CrcCreate(unsigned int *Buf,unsigned int BufLen)//int as byte
{
  unsigned int i,t1,t2,t3;
  unsigned int crcval;
  t1 = Buf[0];
  t2 = Buf[1];
  for(i=2;i<BufLen;i++){
    t3 = Buf[i];
    crcval = CrcTable[t1];
    crcval ^= (t2<<8)+t3;
    t2 = crcval & 0x00ff;//LOW(crcval);
    t1 = crcval >> 8 ;//HIGH(crcval);
  }
  crcval = CrcTable[t1];
  crcval ^= t2<<8;
  t2 = crcval & 0x00ff;//LOW(crcval);
  t1 = crcval >> 8;//HIGH(crcval);
  crcval = CrcTable[t1];
  crcval ^= t2<<8;
  return crcval;  
}

//Create FEC Code
unsigned int CorrectCreate(unsigned int CodeByte1,unsigned int CodeByte2)//int as byte
{
  unsigned long code;
  unsigned long gc;
  int i;
  code = (unsigned long)((CodeByte1<<8)+CodeByte2)<<10;
  gc = (unsigned long)GCORRECT << (26-11);
  for(i=0;i<16;i++){
    if((code & (unsigned long)0x2000000)!=0)
      code ^= gc;
    code <<= 1;  
  }
  return (code >> (26-10));
}

//return 0:no error,1:Correct error,2:error
unsigned int CorrectDeal(unsigned long *CorrectCode)
{
  unsigned long code;
  unsigned long gc;
  unsigned int i,t;
  
  code = *CorrectCode ;
  gc = (unsigned long)GCORRECT << (26-11);
  for(i=0;i<16;i++){
    if((code & (unsigned long)0x2000000)!=0)
      code ^= gc;
    code <<= 1;  
  }
  t = code >> (26-10);
  if(t==0)
    return 0;
  for(i=0;i<26;i++){
    if(t==CorrectErfSample[i]){
      *CorrectCode ^= CorrectTable[i];
      return 1;  
    }
  }
  return 2;
}

//End of file