crc.c

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#define UCHAR unsigned char

#include <stdio.h>
#include <stdlib.h>

void fwdccitthware(data,accum)
UCHAR data;
UCHAR *accum;
{
  UCHAR i,j,tmp1,tmp2,tmp3;
  
  for(i=0;i<8;i++) {
    tmp1=((data<<i)&(0x80))/0x80;
    for(j=16;j>0;j--)
      accum[j]=accum[j-1];
    if ((tmp2=accum[16]^tmp1)==1)
      {
        accum[0]=tmp2;
        accum[5]=accum[5]^1;
        accum[12]=accum[12]^1;}
    else accum[0]=tmp2;
  }
}

void MakeCRCBytes(in, info_dim, CRC_dim)
unsigned char *in;
int info_dim;  /* number of info bytes */
int CRC_dim;  
{

  int i;
  UCHAR *crcbit;  

  crcbit = (UCHAR *) calloc(17, sizeof(UCHAR));
  if (crcbit == NULL) 
    printf("warning: CheckCRC calloc failed\n");

  for(i = 0; i <info_dim; i++)
    fwdccitthware(in[i],crcbit);
  
/*  for(i = 15; i >=0 ; i--)
    printf("%d", crcbit[i]);
  printf("\n");  */

  in[info_dim] = 0;
  in[info_dim+1] = 0;
  for(i = 7; i >= 0; i--){
    in[info_dim] = (in[info_dim] << 1) + crcbit[i+8];
    in[info_dim+1] = (in[info_dim+1] << 1) + crcbit[i];
  } 
  
  free(crcbit);

/*  printf("%d %d\n", in[info_dim], in[info_dim+1]); */
}


int CheckCRC(out_byte, info_dim, CRC_dim)
UCHAR *out_byte; 
int info_dim;
int CRC_dim;
{

  int i, sum=0;
  UCHAR *crcbit;  

  crcbit = (UCHAR *) calloc(17, sizeof(UCHAR));
  if (crcbit == NULL) 
    printf("warning: CheckCRC calloc failed\n");

  for(i = 0; i <(info_dim+CRC_dim); i++)
    fwdccitthware(out_byte[i],crcbit);
  for(i = 0; i < 16; i++)
    sum += crcbit[i];
  
  
  /* printf("\n"); */

  free(crcbit);
  
  if(sum == 0) 
    return 1;
  else 
    return 0;
}

/*
 main()
{
  int i;
  UCHAR in[4];
  
  in[0] = 15;
  in[1] = 17;

  MakeCRCBytes(in, 2, 2);
  for (i=0; i<4;i++)
    printf(" %d\n", in[i]);
  
  in[0] = 14;

  if(CheckCRC(in, 2, 2))
    printf("No error\n");
  else
    printf("Oops! there is error\n");
  
} */

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