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learncheck_sum.c
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learncheck_sum.c
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#include<stdio.h>
#include<string.h>
#include<stdint.h>
#define POLYNOMIAL 0xD8
typedef uint8_t crc;
#define WIDTH (8* sizeof(crc))
#define TOPBIT (1<<(WIDTH-1))
crc crcTable[256];
void crcInit(void)
{
crc remainder;
int dividend,bit;
for(dividend =0; dividend <256; dividend++)
{
remainder = dividend << (WIDTH-8);
for(bit=8;bit>0;--bit)
{
if(remainder & TOPBIT)
{
remainder = (remainder<<1)^POLYNOMIAL;
}
else{
remainder = remainder<<1;
}
}
crcTable[dividend] = remainder;
//printf("%d %d\n",dividend,remainder );
}
}
crc calcCrc(char message[], int n)
{
crc rem =0;
uint8_t data;
int i;
for(i=0;i<n;i++)
{
data = message[i]^((rem>>WIDTH-8));
//printf("%u\n",data );
rem = crcTable[data]^(rem<<8);
}
return rem;
}
int main()
{
FILE *fp;
crcInit();
char message[1000];
fp = fopen("data.txt","r");
if(fp){
size_t newLen = fread(message,sizeof(char),450,fp);
if(ferror(fp)!=0)
{
fputs("Error reading the file",stderr);
}
else{
message[newLen++] = '\0';
}
}
printf("%u\n",calcCrc(message,450));
}