CRC Generator.c

   #include <math.h>
   #include <stdio.h>

   void Display (unsigned char* result, unsigned count)
   {
      for (unsigned i = 0; i < count; ++i)
         printf ("%d", result[i]);
      printf ("\n");
   }

   // Ensure len(left) >= len(right)
   void XOR (unsigned char* left, unsigned char* right, unsigned rN)
   {
      for (unsigned i = 0; i < rN; ++i)
         left[i] = left[i] ^ right[i];
   }

   void CRCGenerate (unsigned char* source, unsigned char* generator, unsigned vN, unsigned gN)
   {
      unsigned char tmp[30];
      for (unsigned i = 0; i < vN; ++i)
         tmp[i] = source[i];

      // Add 0's to classify as Remainder to the end
      unsigned remainderN = gN - 1;
      for (unsigned i = 0; i < remainderN; ++i)
         source[vN + i] = 0;

      // XOR All Values One by One
      for (unsigned i = 0; i < vN; ++i)
      {
         // If it starts with 0, go to next
         if (source[i] == 0)
            continue;
         // If there are enough values left
         if (i + 1 < vN)
            XOR (source + i, generator, gN);
         else
            break;
      }
      for (unsigned i = 0; i < vN; i++)
         source[i] = tmp[i];
   }
   int CRCCHeck (unsigned char* source, unsigned char* generator, unsigned vN, unsigned gN)
   {
      // XOR All Values One by One
      for (unsigned i = 0; i < vN; ++i)
      {
         // If it starts with 0, go to next
         if (source[i] == 0)
            continue;
         // If there are enough values left
         if (i + 1 < vN)
            XOR (source + i, generator, gN);
         else
            break;
      }
      for (unsigned i = vN; i < vN + gN; i++)
         if (source[i] == 1)
            return 0;
      return 1;
   }


   int main ()
   {
      unsigned char values [20] = {1, 1, 1, 0, 0, 0, 1, 0};
      unsigned vN = 8;
      unsigned char generator [] = {1, 1, 0, 0, 1, 1};
      unsigned gN = 6;

      Display (values, vN);
      CRCGenerate (values, generator, vN, gN);
      Display (values, vN + gN - 1);

      printf ("\n\nWith Error\n");
      values[4] = 1;
      Display (values, vN + gN - 1);

      if (CRCCHeck (values, generator, vN, gN))
         printf ("No Error");
      else
         printf ("Error\n");
      return 0;
   }