CRC.c

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <ctype.h>
#define CRC_A 1
#define CRC_B 2
#define BYTE unsigned char
unsigned short UpdateCrc(unsigned char ch, unsigned short *lpwCrc)
{
  ch = (ch^(unsigned char)((*lpwCrc) & 0x00FF)); 
  ch = (ch^(ch<<4));

  *lpwCrc = (*lpwCrc >> 8)^((unsigned short)ch << 8)^((unsigned short)ch<<3)^((unsigned short)ch>>4);
  return(*lpwCrc);
}
void ComputeCrc(int CRCType, char *Data, int Length,
  BYTE *TransmitFirst, BYTE *TransmitSecond)
{
  unsigned char chBlock; 
  unsigned short wCrc;
  switch(CRCType) {
    case CRC_A:
    wCrc = 0x6363; // ITU-V.41
    break;
    case CRC_B:
      wCrc = 0xFFFF;  // ISO 3309
      break;
      default:
      return; 
    }
    do {
      chBlock = *Data++; 
      UpdateCrc(chBlock, &wCrc);
    } while (--Length);
    if (CRCType == CRC_B)
        wCrc = ~wCrc; // ISO 3309
      *TransmitFirst = (BYTE) (wCrc & 0xFF);
      *TransmitSecond = (BYTE) ((wCrc >> 8) & 0XFF);
      return; 
    }
    BYTE BuffCRC_A[10] = {0x12, 0x34};
    BYTE BuffCRC_B[10] = {0x0A, 0x12, 0x34, 0x56}; 
    unsigned short Crc;
    BYTE First, Second;
    FILE *OutFd;
    int i;
    int main(void)
    {
      printf("CRC-16 reference results 3-Jun-1999\n");
      printf("by Mickey Cohen - mickey@softchip.com\n\n"); 
      printf("Crc-16 G(x) = x^16 + x^12 + x^5 + 1\n\n");
      printf("CRC_A of [ ");
      for(i=0; i<2; i++) printf("%02X ",BuffCRC_A[i]); 
        ComputeCrc(CRC_A, BuffCRC_A, 2, &First, &Second); 
      printf("] Transmitted: %02X then %02X.\n", First, Second);

      printf("CRC_B of [ ");
      for(i=0; i<4; i++) printf("%02X ",BuffCRC_B[i]); 
        ComputeCrc(CRC_B, BuffCRC_B, 4, &First, &Second); 
      printf("] Transmitted: %02X then %02X.\n", First, Second);
      return(0); 
    }