crc8 C implementation

crc8

// c = t%(m+1)
// T - итоговая сумма, M - макс допустимое значение контрольной суммы
#include <stdio.h>
#define MAX 256
#define POLYNOMIAL 0x81  

FILE *file;


unsigned char crc8(unsigned int len)
{
  unsigned char crc = 0x00, symbol = fgetc(file);
  // int count = 0;
  while (len--)
  {
      crc ^= symbol;  // сложение

      for (int bit = 8; bit > 0; --bit)
      {
        crc = (crc << 1);
        if (crc & 0x80)
            crc ^= POLYNOMIAL;
          // crc = (crc << 1);
      }
      symbol = fgetc(file);
      // count++;
      // if (count == 999)
      // {
      //     printf("%c\n", symbol);
      // }
  }

  return crc;
}


int main()
{
    int result, i = 0, symbol, count = 0;
    file = fopen("text.txt", "r");
    symbol = fgetc(file); // берет символ переноса
    while(symbol != EOF)
    {
      i += symbol;
      symbol = fgetc(file);
      count++;

    }
    // printf("%d\n", i);
    // printf("%d\n", count);
    result = i%MAX;
    printf("check sum: %d\n", result);
    fclose(file);
    file = fopen("text.txt", "r");
    printf("CRC8: %d\n", crc8(count));
    fclose(file);
    return 0;
}

There is a bug in line 21!
You need to extract the msb before shifting the crc:

int msb = (crc >> 7) & 1;
crc <<= 1
if(msb){
   crc ^= POLYNOMAL;
}