/*
 * CRC routines needed for DOCSIS
 *
 * 
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "crc.h"

/* Global table data for the functions.  Must call 'crctabinit' before using. */
static unsigned int  crc16tab[256];
static unsigned int  crc16tabnew[256];
static unsigned long crc32tab[256];

/* Globals used to compute CRCs */
static unsigned long CRC;
static unsigned int  HCS;

/* Local working functions */
unsigned long	calc32crc(unsigned int C);
unsigned int	calc16crc(unsigned int C);
void		crctabinit(void);

/* #define MAIN*/
#ifdef MAIN
main(int argc, char **argv) {
   unsigned char test1[200];
   unsigned short crc16;
   unsigned long  crc32;
   
   unsigned char ieeetest[] 
   	= {	0x01, 0xE0, 0x2F, 0x00, 0x00, 0x01, 
   		0x01, 0xE0, 0x2F, 0x00, 0x00, 0x02,
   		0x00, 0x0A,
   		0x00, 0x00, 0x03, 0x01, 0x01, 0x00,
   		0x09, 0x0A, 0x0B, 0x0C
   	}; // The CRC32 that should be appended is: D5 D9 DC E9

   			
   /* initialize CRC engines */
   initialize_crc();
   
   test1[0] = 0xC0;
   test1[1] = 0x00;
   test1[2] = 0x00;
   test1[3] = 0x1C;
   crc16 = compute_crc16 (test1, 4);
   printf ("\nTest string is: C0 00 00 1C, crc16=%x\n", crc16);

   crc32 = compute_crc32 (ieeetest, 24);
   printf ("\ncrc32=%x\n", crc32);

   test1[0] = 0x01;
   test1[1] = 0x05;
   test1[2] = 0x00;
   test1[3] = 0x2b;
   test1[4] = 0x44;
   test1[5] = 0x01;
   test1[6] = 0xba;
   test1[7] = 0x64;
   test1[8] = 0x00;
   //ba
   //c8
   crc16 = compute_crc16 (test1, 9);
   printf ("\nTest string is: 01 05 .. 64 00, crc16=%x\n", crc16);
   
} /* end of main */
#endif

void initialize_crc ()
{
   crctabinit();
}

void crctabinit(void)
{
  int i,n;
  unsigned long CRC32;
  unsigned int  CRC16;

  for (i=0;i<256;i++) {
     CRC32=i;
     for (n=1;n<9;n++) {
        if (CRC32 & 1)
           CRC32 = (CRC32 >> 1) ^ /* XOR */ 0xedb88320;
        else
           CRC32 = CRC32 >> 1;
      }
      crc32tab[i] = CRC32;
   }

   for (i=0;i<256;i++) {
      CRC16=i;
      for (n=1;n<9;n++) {
         if (CRC16 & 1)
            CRC16=(CRC16 >> 1) ^ 0xA001;
         else
            CRC16=CRC16 >> 1;
      }
      crc16tab[i]=CRC16;
   }

   for (i=0;i<256;i++) {
      CRC16=i;
      for (n=1;n<9;n++) {
         if (CRC16 & 1)
            CRC16=(CRC16 >> 1) ^ 0x8408;
         else
            CRC16=CRC16 >> 1;
      }
      crc16tabnew[i]=CRC16;
   }
}        

unsigned long compute_crc32 (unsigned char *p, int n)
{
   int i;
   unsigned long x, swapped_x;
   
   CRC = 0xffffffffL;
   for (i=0; i<n; i++) {
      x = calc32crc(*p++);
   }
   /* Swap bytes in crc value */
   swapped_x  = ((x << 24) & 0xFF000000);
   swapped_x |= ((x <<  8) & 0x00FF0000);
   swapped_x |= ((x >>  8) & 0x0000FF00);
   swapped_x |= ((x >> 24) & 0x000000FF);
   return swapped_x;
}

unsigned short compute_crc16 (unsigned char *p, int n)
{
   int i;
   unsigned short x, swapped_x;
   
   HCS = 0xffff;
   for (i=0; i<n; i++) {
      x = calc16crc(*p++);
   }
   
   /* Swap bytes in crc value */
   swapped_x  = x << 8;
   swapped_x |= x >> 8;
   return swapped_x;
}


/* CCITT CRC-32 */
unsigned long calc32crc(unsigned int C) {
   CRC=crc32tab[(CRC ^ C) & 0xFF] ^ ((CRC>>8) & 0x00ffffffL);
   return CRC ^ 0xffffffffL; 
}

/* CCITT CRC-16 */
unsigned int calc16crc(unsigned int C) {
   HCS=((HCS >> 8) & 0x00ff) ^ crc16tabnew[(HCS ^ C) & 0x00ff];
   return HCS ^ 0xffff;
}